GB2618147A

GB2618147A - Monitoring air quality

Info

Publication number: GB2618147A
Application number: GB2206314.3A
Authority: GB
Inventors: Edward Mills James; Andrew Jones Timothy; Henry Campbell Terry-Collins James
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2023-11-01
Also published as: GB202206314D0; WO2023209353A1

Abstract

A system to quantify an amount of rebreathed air inhaled by a person by measuring a concentration of carbon dioxide in air 302 with a carbon dioxide sensor (102, fig.1), measuring a person’s heart rate 308 or breathing rate using a heart rate sensor (104, fig.1) or breathing rate sensor, quantifying an amount of air inhaled by the person 312 based on their measured heart rate or breathing rate, quantifying a fraction of air that is rebreathed air 314 based on the measured concentration of carbon dioxide in the air, and quantifying an amount of rebreathed air inhaled by the person 316 based on the quantified amount of air inhaled and the fraction of air that is rebreathed air. The system may additionally measure an atmospheric condition, or electromagnetic radiation to determine whether the person is indoors and may delay quantification if the person is not indoors. Quantification may also be based on a physiological characteristic, such as age, gender or weight, or based on a number of other persons in the vicinity.

Description

MONITORING AIR QUALITY

Field of the Disclosure

The present disclosure relates to monitoring air quality.

Background of the Disclosure

Poor ventilation in an occupied indoor environment can detrimentally expose occupiers to elevated levels of air previously exhaled by the occupiers. Elevated levels of exhaled air can undesirably affect people in the indoor environment, for example, by exposing them to elevated levels of exhaled gases, such as carbon dioxide, which may impair their cognitive performance, and/or exposing them to an increased level of airborne contaminants, such as viruses. An approach to informing occupiers of air quality is to provide a metric representing a concentration of a constituent gas in the air, for example, a carbon dioxide concentration.

Summary of the Disclosure

A first aspect of the present disclosure provides a system for quantifying an amount of air inhaled by a person that is rebreathed air, the system comprising: a carbon dioxide sensor responsive to carbon dioxide in air; a heart rate sensor or a breathing rate sensor responsive to a person's heart rate or breathing rate respectively; one or more processors, and one or more memory devices storing machine-readable instructions, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to: measure a concentration of carbon dioxide in air using the carbon dioxide sensor, measure the person's heart rate or breathing rate using the heart rate sensor or the breathing rate sensor respectively, and instruct execution of computational operations to: quantify an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate, quantify a fraction of air that is rebreathed air based on the measure of the concentration of carbon dioxide in the air, and quantify an amount of air inhaled by the person that is rebreathed air based on the quantified amount of air inhaled by the person and the quantified fraction of air that is rebreathed air.

The system is thus operable to quantify an amount of air inhaled by the person that is rebreathed air, i.e., air that has previously been exhaled by a person. The person may advantageously find the 'rebreathed amount' quantity to be a relatively informative metric of poor air quality/ventilation. In comparison, users may find a metric representing a concentration of a constituent gas in the air, for example, a carbon dioxide concentration, to be relatively uninformative. For example, they may be unaware of what may be considered a normal or good concentration of the particular gas, and thus may not recognise the significance of the reported concentration. Whereas, the person may more easily comprehend the significance of inhaling a high volume of rebreathed air. As a result, the user may more easily recognise a condition of poor air quality/ventilation, and take practical actions to mitigate the condition, for example, improving ventilation of a room. Consequently, the user's exposure to air-borne pollution resulting from poor ventilation may desirably be reduced.

The system may comprise both the heart rate sensor and the breathing rate sensor. The machine-readable instructions may accordingly be executable by the processor(s) to cause the processor(s) to measure both the person's heart rate using the heart rate sensor and the person's breathing rate using the breathing rate sensor, and subsequently quantify the amount of air inhaled by the person based on both the measure of the person's heart rate and the measure of the person's breathing rate. Using both the measure of the person's heart rate and the measure of their breathing rate in the computation of the amount of air inhaled may desirably improve the accuracy of the quantification. Alternatively, to reduce cost and/or complexity, the system may comprise only one of the heart rate sensor and breathing rate sensor.

The various hardware components of the system may be co-located in a unitary assembly. For example, two or more of the carbon dioxide sensor, breathing rate sensor, heart rate sensor, processor(s) and/or the memory device(s) could be incorporated into a single assembly, such as a portable device. Alternatively, those components could be located mutually remotely, distributed amongst different discrete assemblies. For example, one or more of the sensors could be incorporated in a first device, such as a portable device, and one or more of the processor(s) or the memory device(s) could be incorporated in one or more further devices, such as in a datacentre. The one or more processors could comprise a single processor, and all of the machine-readable instructions could be executed by that single processor. Alternatively, the one or more processors could comprise plural processors, and each processor could execute a respective subset of the machine-readable instructions. For example, a first processor could be responsible for executing the machine readable instructions to measure a concentration of carbon dioxide in air using the carbon dioxide sensor and measure the person's heart rate or breathing rate using the heart rate sensor or the breathing rate sensor respectively. The first processor could then 'offload' execution of the later computational operations, to perform the various quantifications, to one or more further processors. Similarly, the one or more memory devices could comprise a single memory device storing all of the machine-readable instructions. Alternatively, plural memory devices could be provided, each memory device storing a respective subset of the machine-readable instructions.

The fraction of air that is rebreathed (which may also be referred to herein as a rebreathed fraction) is an estimate of the fraction of air in a local environment which has previously been inhaled and then exhaled, for example, by a person or animal. This can be calculated using the measure of the concentration of carbon dioxide in air from the carbon dioxide sensor, along with estimates (or, in some examples, measurements) of an exhaled carbon dioxide concentration and a reference carbon dioxide concentration. The rebreathed fraction,. f may be calculated according to the formula: f(Cmcus-Cref) ( 1) Cern where Crneas is a carbon dioxide concentration which is measured using a carbon dioxide sensor; Crec is a measurement or an estimate of an average or a typical carbon dioxide concentration (which may be derived from a measurement taken outdoors, for example), and Cexh is a measurement or an estimate of an exhaled carbon dioxide concentration.

As an example, the current average atmospheric carbon dioxide concentration of 415 ppm may be taken as an estimate of Cref. The concentration of carbon dioxide in exhaled breath can vary from 36000 ppm to 43000 ppm, and so the middle of this range (39500 ppm) may be taken as an estimate of Cexti. By using this formula, for example, a system according to embodiments of the present invention may quantify a fraction of air that is rebreathed air based on a measure of the concentration of carbon dioxide in air by the carbon dioxide sensor.

In examples, the system may comprise an attachment apparatus for attaching one or more of the carbon dioxide sensor, the heart rate sensor, or the breathing rate sensor to the person. In other words, the system could comprise a wearable device for attaching to the person's body. The attachment apparatus could comprise, for example, a strap for encircling a limb of the person, or a garment for wearing by the person, or an alternative apparatus for attaching to a person.

By attaching sensors to the person, the accuracy of the measurement of the respective sensor may be improved. For example, by attaching the carbon dioxide sensor to the person, the sensor may be exposed to the same air that the person inhales, even if that person moves, and thus may provide a highly representative measurement of the concentration of carbon dioxide in the air that the person inhales. In comparison, if the carbon dioxide sensor were not attached to the person, for example, if the sensor were located in a static position in a room occupied by the person, the sensor may not be exposed to the same air that the person inhales, at least over a short time scale. For example, concentrations of carbon dioxide could vary with respect to the area of the room, and thus a static sensor measurement could be less representative of the concentration of carbon dioxide in the air to which the person is exposed. Similarly, by attaching one or both of the heart rate sensor and the breathing rate sensor to the person, the sensors are brought closer to the person, and thus may provide more accurate measurements, in particular if the person moves. In comparison if, for example, the heart rate sensor comprised a static sensor, such as an optical camera, the person could move out of the field-of-view of the sensor, and thus the sensor measurement would be negatively affected.

S

In examples, the system comprises a wireless communication interface for interfacing with a wireless communication network, and the machine-readable instructions are executable by the one or more processors to cause the processors to output, by the wireless communication interface to the wireless communication network: data representing the measure of the person's heart rate or breathing rate and the measure of the concentration of carbon dioxide in air, and the instructions to execute the computational operations.

In other words, the system could involve one or more first processors executing the machine-readable instructions to measure a concentration of carbon dioxide in air using the carbon dioxide sensor and measure the person's heart rate and/or the breathing rate using the heart rate sensor and/or the breathing rate sensor. These one or more first processors could be incorporated in a device along with the various sensors. For example, the sensors and the one or more first processors could be incorporated in a portable device, such as a wearable device. The processor(s) of this first device could then 'offload' execution of the later computational operations, to perform the various quantifications, to one or more further processors. Thus, the processor(s) of the first device may transmit to the one or more further processors, via the wireless communication interface, the sensor measurements, and the instruction to execute the later quantification computational operations. This 'offloading' approach reduces the computational burden on the one or more first processors. This may desirably enable the first processor(s) to have a relatively low computational capacity, and/or may reduce the electrical power consumption of the first processor(s). This may desirably enable a device incorporating the first processors to be relatively compact, as the size of the first processor(s) and/or a battery for powering the first processor(s) may be relatively small.

This compactness may advantageously facilitate configuration of the sensors and one or more first processors into a portable package, for example, into a package that is suitable for wearing by the person. The wireless communication network could, for example, be a Wi-Fi, Bluetooth, Bluetooth Low Energy or Zigbee network, and the interface may be configured accordingly.

In examples, the machine-readable instructions are executable by the one or more processors to cause the processors to execute the computational operations.

In other words, the one or more processors may not just issue instructions to execute the various quantification computational operations, for example, 'offloading' instructions to one or more further processors to execute the computational operations. Instead, the one or more processors may themselves execute the various computational operations. In comparison to the aforementioned 'offloading' approach, this onboard approach may desirably improve the data security of the sensor measurements, as they are not required to be shared with further processors, e.g., via the wireless network. Additionally, latency or delay in the computations, resulting from outputting the measurements via the network, may be avoided.

In examples, the machine-readable instructions are executable by the one or more processors to cause the one or more processors to output a representation of the quantified amount of air that is rebreathed air.

The user of the system may thus be informed of the quantified amount of air. The representation could, for example, comprise data representing the quantified amount of air, and the data could be output via the wireless communication interface over a wireless network. As an example alternative, the processors could interface with a visual or audible output device, to output a visual or audible representation of the quantified amount of air.

In examples, the system comprises an electronic display, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to display on the electronic display a visual representation of the quantified amount of air that is rebreathed air. The visual representation may be easily understandable by the user, and may thus allow the user to easily comprehend the quantified amount of air, and thus easily gain an understanding of the air quality/ventilation rate of the locality.

In examples, the machine-readable instructions are executable by the one or more processors to cause the processors to: measure an atmospheric condition and/or electromagnetic radiation using the carbon dioxide sensor and/or a further sensor, determine whether the measured atmospheric condition and/or electromagnetic radiation is greater or lesser than a reference value, and proceed with the instructing execution of the computational operations in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is one of greater or lesser than the threshold value, else delay the instructing execution of the computational operations in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is the other of greater or lesser than the reference value.

In other words, the system could instruct execution of the computational operations in dependence on the measured atmospheric conditions/electromagnetic radiation. This feature may desirably enable execution of the computational operations only in certain conditions. In particular, in some applications it is desirable for the computational operations to be performed only when the sensors are located inside a building, inasmuch that the issue of ventilation and exposure to high levels of rebreathed air may typically only be highly relevant when the person is indoors. This is particularly relevant where the system, or at least the portion of the system incorporating the sensors, is portable, such as being wearable, whereby the system may be carried about with the person, both indoors and outdoors. Executing the computational operations only when the sensors are determined to be indoors may desirably avoid unnecessary performance of the computational operations when the person is outdoors. Thus, unnecessary consumption of processor resource, and/or electrical power consumption, may be reduced.

The atmospheric conditions/electromagnetic radiation may be reliable indicators of whether the sensors are indoors or outdoors For example, atmospheric conditions such as concentration of a gas in the air, air temperature and/or humidity may reliably vary between indoors and outdoors. For example, in an indoor environment it may be expected that concentrations of a gas, such as carbon dioxide, in the air may be higher than in an outdoor environment. Thus, a high concentration of a gas such as carbon dioxide in the air may be indicative of the sensors being located indoors. Similarly, it may be expected that, dependent on climate, the temperature and/or humidity may be lower indoors than outdoors, or vice versa. The existence of high levels of electromagnetic radiation, such as radio frequency radiation originating from wireless routers, may also be considered indicative of the sensor being located indoors. Alternatively, a weak cellular telephone signal could be considered indicative of the further sensor being indoors. Thus, the further sensor could, for example, be a cellular transceiver, operable to measure a cellular signal strength. The measuring an atmospheric condition could involve the aforementioned operation of measuring a carbon dioxide concentration in the air using the carbon dioxide sensor. Alternatively, measuring an atmospheric condition could involve measuring an alternative atmospheric condition, such as measuring a concentration of an alternative gas in air using a further gas sensor, or measuring air temperature and/or humidity using a temperature/humidity sensor respectively.

The reference value may thus be a predefined threshold value corresponding to a level of the particular condition to be measured that corresponds to an indoor environment. For example, where the atmospheric condition to be measured is a carbon dioxide concentration in air, the reference value could be a predefined value defining a lower bound for a concentration of carbon dioxide in air that may be expected to occur in an indoor environment but not typically in an outdoor environment. Thus, in such example, where the carbon dioxide concentration, or other atmospheric condition metric, is determined to be greater that the reference value, indicating that the sensors are located in an indoors environment, the processors may proceed to instruct the quantification computational operations. In the alternative, where the measured atmospheric condition/electromagnetic radiation level is less than the reference value, indicating that the sensors are located in an outdoors environment, the processors may delay instructing execution of the computational operations. In other words, in response to determining that the measured atmospheric condition and/or electromagnetic radiation is the other of greater or lesser than the threshold value, indicating that the sensor is outdoors, the processors may introduce a pause to thereby delay the instructing execution of the computational operations. Thus, unnecessary execution of the computational operations, when the sensor is outdoors, is avoided, and thereby processor resource and associated processor power consumption may be reduced.

In examples, the machine-readable instructions are executable by the one or more processors to cause the processors to: measure an atmospheric condition and/or electromagnetic radiation using the carbon dioxide sensor and/or a further sensor, repeatedly measure the atmospheric condition and/or the electromagnetic radiation using the carbon dioxide sensor and/or the further sensor after a period of time has elapsed since the measuring an atmospheric condition and/or electromagnetic radiation, quantify a difference between the measurement of the atmospheric condition and/or the electromagnetic radiation and the repeat measurement of the atmospheric condition and/or the electromagnetic radiation, determine whether the difference between the measurement of the atmospheric condition and/or the electromagnetic radiation and the repeat measurement of the atmospheric condition and/or the electromagnetic radiation is one of greater or lesser than a threshold difference, and proceed with the instructing execution of the computational operations in response to determining that the difference is one of greater or lesser than a threshold difference else delay the instructing execution of the computational operations in response to determining that the difference is the other of greater or lesser than the threshold difference.

In other words, the computational operations could be executed in dependence on a relative trigger, the relative trigger being the difference between the measure and the repeat measure. This approach may desirably compensate for macro-level changes in the measured condition. For example, where the measured atmospheric condition is air temperature, this approach may compensate for different climates, inasmuch that the execution is performed based on changes in temperature rather than absolute temperature. A rapid change in temperature, for example, may be expected to occur when a user transits between indoor and outdoor environments. For example, in some applications, a rapid and substantial increase in temperature may be expected to indicate a user entering an indoor environment from an outdoor environment The step of measuring the atmospheric condition could be the aforementioned step of measuring carbon dioxide concentration using the carbon dioxide sensor. Alternatively it could comprise, for example, measuring an alternative gas concentration, a temperature and/or a humidity using a further sensor.

Thus, by this approach a determination may be made as to whether the sensor is located indoors or outdoors, and unnecessary execution of the computational operations, when the sensor is determined to be outdoors, may be avoided Thereby processor resource and associated processor power consumption may be reduced.

In examples, the one or more memory devices store data defining a reference value, the machine-readable instructions are executable by the one or more processors to cause the processors to: determine whether the measured concentration of carbon dioxide in the air is greater or lesser than the reference value; and in response to determining that the measured concentration of carbon dioxide in the air is one of greater or lesser than the reference value, proceed with the instructing execution of the computational operations.

In examples, the machine-readable instructions are executable by the one or more processors to cause the processors to: in response to determining that the measured concentration of carbon dioxide in the air is the other of greater or lesser than the reference value, delay the instructing execution of the computational operations and repeat the measuring a concentration of carbon dioxide in the air using the carbon dioxide sensor after a period of time has elapsed.

In examples, the machine-readable instructions may be executable by the processors to cause the processors to provide a prompt to the person, to identify whether the person is indoors or outdoors. For example, such a prompt may be provided responsive to a determination that the system may be indoors as described above, or such a prompt may be provided periodically or at certain times of the day. Such a prompt may involve outputting an indication to the user (e.g. via a display device) that they should input whether they are indoors or outdoors This may thus facilitate determination of whether the person is indoors or outdoors, and thereby allow execution of the computational operations only when the person is indoors.

In examples, the machine-readable instructions are further executable by the one or more processors to cause the processors to instruct retrieval of data defining a physiological characteristic of the person, and the instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate comprises instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate and the physiological characteristic.

In other words, the computational operations for quantifying the amount of air inhaled may further take account of a physiological characteristic of the person, the physiological characteristic being a characteristic expected to influence the amount of air inhaled. For example, the physiological characteristic could comprise the age, gender or weight of the person. These example characteristics may be expected to influence the person's lung capacity, and accordingly may be expected to influence the amount of air inhaled by the person. Thus, by taking account additionally of the physiological characteristic the accuracy of the quantification of the amount of air inhaled, and thus the rebreathed fraction, may be improved.

For example, based on the physiological characteristic, it may be possible to estimate a user's minute ventilation rate (Vs), which is the volume of gas inhaled into or exhaled from the person's lungs per minute (for example in litres per minute), from their heart rate (HR) and gender using the equations (see Minute ventilation of cyclists, car and bus passengers: an experimental study; Zuurbier et. al. -Environmental Health, 2009): VE(rnale) = el.03+0.021HR e0.57+0.023HR VE(female) = In examples where data defining a physiological characteristic is not retrieved, it may be possible to estimate a user's minute ventilation rate (VE) from their heart heat (HR) according to the equation (see An approach to using heart rate monitoring to estimate the ventilation and load of air pollution exposure; Cozza et al; Science of The Total Environment; 2015; 520:160-7): vE = e0.58+0.025HR (4) Based on this determined ventilation rate, a total rebreathed air volume, RA V, for a given time, T, can be calculated, using the rebreathed fraction, / according to the equation: R AV = Ero' VE(t) x f (t) (5) In examples, the machine-readable instmctions are executable by the one or more processors to cause the processors to: obtain an indication of a number of other persons in the vicinity of the person; and instruct the execution of the computational operation to quantify the fraction of air that is rebreathed air based on the measure of the concentration of carbon dioxide in air by the carbon dioxide sensor and based on the indication of the number of other persons in the vicinity.

In other words, the quantification of the fraction of rebreathed air may further take account of the number of other persons in the vicinity of the user, for example, in a same indoor room as the user. This may desirably allow for compensation of the quantification depending on the number of other persons who may be expected to have exhaled the air that the person inhales. Thus, the quantification may reflect only air that has previously been exhaled by other persons, not air which has previously been exhaled by the person themselves. Such an arrangement may be particularly advantageous in that the quantification may be more representative of a virus transmission risk, as the rebreathed air fraction which is due to a user of the system themselves is not relevant for virus transmission.

The rebreathed fraction,f may in this case be calculated according to the formula: f(CT, Cr, x n (6) Cexh it Where n is the number of persons in a given location including the user (which may be referred to herein as the occupancy of a room or area), Cmeas is a measurement of a carbon dioxide concentration, such as a carbon dioxide concentration which is measured using a carbon dioxide sensor, Cref is a measurement or an estimate of an average or typical carbon dioxide concentration (which may be derived from a measurement taken outdoors, for example, outdoors), and Ceth is a measurement or an estimate of an exhaled carbon dioxide concentration. As an example, the current average atmospheric carbon dioxide concentration of 415 ppm may be taken as an estimate of Coui. The concentration of carbon dioxide in exhaled breath can vary from 36000 ppm to 43000 ppm, and so the middle of this range (39500 ppm) may be taken as an estimate of Ce'h.

By using this formula, for example, a system according to embodiments of the present invention may quantify a fraction of air that is rebreathed air due to other people, based on a measure of the concentration of carbon dioxide in air by the carbon dioxide sensor and the indication of a number of other persons in the vicinity of the person. This may provide improved personalised air quality monitoring, the results of which may be output on an electronic display, as described above.

In examples, the machine-readable instructions may be executable by the processors to cause the processors to provide a prompt to the person, to request input of the number of other persons in their vicinity. For example, such a prompt may be provided responsive to a determination that the system is indoors as described above. Such a prompt may involve outputting an indication to the user (e.g. via a coupled display device) that they should input the number of other persons in the vicinity. The received number may be stored in the one or more memory devices, for example. In embodiments, the person may enter this number to a wearable device or a remote device as described above.

A second aspect of the present disclosure provides, a method for quantifying a volume of air inhaled by a person that is rebreathed air, the method comprising: measuring a concentration of carbon dioxide in air to which the person is exposed using a carbon dioxide monitor, and measuring the person's heart rate or breathing rate using a heart rate monitor or a breathing rate monitor, instructing quantification of: an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate, a fraction of air that is rebreathed air based on a measure of the concentration of carbon dioxide in air by the carbon dioxide monitor, and a volume of air inhaled by the person that is rebreathed air based on the quantified amount of air inhaled by the person and the quantified fraction of air that is rebreathed air.

In examples, the method further comprises: measuring an atmospheric condition and/or electromagnetic radiation using the carbon dioxide monitor and/or a further monitor, determining whether the measured atmospheric condition and/or electromagnetic radiation is greater or lesser than a reference value, and proceeding with instructing quantification in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is one of greater or lesser than the threshold value, else delaying instructing quantification in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is the other of greater or lesser than the threshold value In examples, the method further comprises: measuring an atmospheric condition and/or electromagnetic radiation using the carbon dioxide monitor and/or a further monitor, repeatedly measuring the atmospheric condition and/or the electromagnetic radiation using the carbon dioxide monitor and/or the further monitor after a period of time has elapsed since the measurement an atmospheric condition and/or electromagnetic radiation, determining whether a difference between the measurement of the atmospheric condition and/or the electromagnetic radiation and the repeat measurement of the atmospheric condition and/or the electromagnetic radiation is one of greater or lesser than a threshold difference, and proceeding with instructing quantification in response to determining that the difference is one of greater or lesser than a threshold difference else delaying instructing quantification in response to determining that the difference measured atmospheric condition and/or electromagnetic radiation is the other of greater or lesser than the threshold difference.

In examples, the method further comprises: determining whether the measured concentration of carbon dioxide in the air is greater or less than a reference value; and in response to determining that the measure concentration of carbon dioxide in the air is one of greater or lesser than the reference value, proceeding with instructing execution of the computational operations.

In examples, the method further comprises: in response to determining that the measured concentration of carbon dioxide in the air is the other of greater or lesser than the reference value, delaying instructing quantification and repeating the measuring a concentration of carbon dioxide in the air using the carbon dioxide monitor after a period of time has elapsed.

In examples, the method further comprises: instructing retrieval of data defining a physiological characteristic of the person, and instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate comprises instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate and the physiological characteristic.

In examples, the method further comprises: obtaining an indication of a number of other persons in the vicinity of the person; and instructing the quantification of the fraction of air that is rebreathed air based on the measure of the concentration of carbon dioxide in air by the carbon dioxide monitor and based on the indication of the number of other persons in the vicinity.

Brief Description of the Drawings

In order that the present disclosure may be more readily understood, embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a system according to an embodiment of the present disclosure, Figure 2 is a schematic diagram of a system according to a second embodiment of the

present disclosure,

Figure 3 is a flow chart showing a method according to the present disclosure and Figure 4 depicts a computing system according to the present disclosure.

Detailed Description of the Disclosure

Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art All documents mentioned in this text are incorporated herein by reference.

Fig. 1 shows a schematic diagram of a system 100 which can be used to monitor air quality by quantifying an amount of air inhaled by a person that is rebreathed air, according to an embodiment of the present invention. The system 100 comprises a carbon dioxide sensor 102 which is responsive to carbon dioxide in air, a heart rate sensor 104 which is responsive to a person's heart rate; a breathing rate sensor 106 which is response to a person's breathing rate; an atmospheric condition sensor 108 which is responsive to an atmospheric condition such as temperature or humidity; an electromagnetic radiation sensor 110 which is responsive to electromagnetic radiation such as visible light or mobile telecommunications network strength; a processor 112 for executing machine-readable instructions to measure and quantify parameters as explained in more detail below; a memory device 114 for storing the machine-readable instructions and any other necessary data; and an electronic display 116 which may display a visual representation of parameters output from the processor 110 in any suitable form to be viewed by the person using the system 100. The components of the system 100 are in communication via a communication network 118, which may be a wired network (e.g. a bus), a wireless network, or any combination of wired and wireless networks, according to the manner in which the system is implemented. The system 100 may thereby monitor air quality by quantifying an amount of air inhaled by a person that is rebreathed air, as explained in more detail below. Although not shown in Fig. 1, the system 100 further comprises at least one power source for powering the various components of the system 100. This may be in the form of mains power, for example, or a battery or supercapacitor, or the like.

The carbon dioxide sensor 102 may be any suitable sensor which is responsive to carbon dioxide in air, for example a photoacoustic sensor such as a Sensirion (trade mark) SCD4x carbon dioxide sensor. The carbon dioxide sensor 102 thereby allows measurement of a carbon dioxide concentration by the system 100. Preferably, the system 100 is configured such that the carbon dioxide sensor 102 is situated in air in a vicinity of the person using the system 100 (e.g. the carbon dioxide sensor 102 may be located adjacent to the person) to ensure accuracy of the carbon dioxide measurement.

The heart rate sensor 104 is preferably a photoplethysmography sensor or pulse oximeter, and so in certain embodiments the heart rate sensor 104 may be provided in a device which is in contact with the person's skin, for example in a wearable device. In some embodiments, the heart rate which is measured using the heart rate sensor 104 may be used to measure or calculate the person's breathing rate. For example, this device may also include the carbon dioxide sensor 102 so that the carbon dioxide sensor 102 is located adjacent to the person.

In the system 100 of Fig. 1 a breathing rate sensor 106 is also used to directly respond to and thereby measure the person's breathing rate, and this measurement may be used to corroborate or compare with the measurement of the person's breathing rate obtained from the heart rate sensor 104 for increased accuracy. For example, the breathing rate sensor 106 may comprise a carbon dioxide sensor, temperature sensor or an anemometer which is preferably located near a person's mouth such that the breathing rate may be inferred from the variation of measurements received from those sensors. In other embodiments, the breathing rate sensor 106 may be a chest mounted device which is configured to be responsive to the expansion and contraction of the person's chest and so derive a breathing rate from those measurements. Optionally, the breathing rate sensor 106 may be provided in a device which is remote from the person, such as a room fan, and may infer the person's breathing rate based on images and/or video captured by a camera system.

The atmospheric condition sensor 108 and/or the electromagnetic radiation sensor HO are used to determine whether the person is indoors or in an enclosed space. Outdoor environments are likely to be well-ventilated so the air quality of such environments is likely to be high, and air-quality monitoring in these environments would therefore be an inefficient use of system 100 resources. By limiting processing of data to indoor environments, system 100 resources (for example, any batteries which are used to power the system 100) may be utilised more efficiently. In embodiments, the atmospheric condition sensor 108 may be any one or more of a temperature sensor, a humidity sensor, or an additional carbon dioxide sensor. Such a sensor may be used to determine when a person is indoors, for example by comparing a sensed value with a threshold value or by monitoring a change in a sensed atmospheric condition over time, as will be explained in more detail below. The electromagnetic radiation sensor 110 may be utilised in a similar manner in order to determine whether a person is indoors or in an enclosed environment. For example, the electromagnetic radiation sensor 110 may be sensitive to visible light and/or a signal strength of a mobile telecommunications network such that whether a person is indoors or outdoors may be determined based on comparison of a sensed value with a threshold value or by monitoring the change in a sensed value over time. It will be appreciated that in certain embodiments, a system may be provided wherein the carbon dioxide sensor 102 is utilised as an atmospheric condition sensor 108 such that no additional sensors are required.

It should be noted that the system 100 may be provided as a unitary device or may be provided with components of the system 100 in different devices. For example, in a preferred embodiment, the carbon dioxide sensor 102 and the heart rate sensor 104 are provided in a portable (e.g. wearable) device which has a communications interface for interfacing with a communications network such that processing of sensed values and display of information to the person can be carried out on another device which forms part of the system 100. Such an embodiment is described in more detail below with respect to Fig. 2. Of course, the system 100 may comprise more than two devices. For example, in certain embodiments, the breathing rate sensor 106 may be provided in a device which is remote from a person, such as a room fan for example, to monitor a breathing rate using a camera system.

Fig. 2 shows a schematic diagram of a system 200 which can be used to monitor air quality by quantifying an amount of air inhaled by a person that is rebreathed air according to a second embodiment of the present invention. In this embodiment, the system 200 comprises a wearable device 210 and a smartphone 220 which are in communication with one another via a communication network shown by arrow 230. A person may input additional data 240 into the system 200 by interacting with the smartphone 220. For example, an application may be run on the smartphone 220 for receiving information from and presenting information to the person using the system.

The wearable device 210 comprises an attachment apparatus in the form of a strap 216 for attaching the wearable device 210 to the person. For example, the strap 216 may be sized to fit on the person's arm, for example around an upper arm or a wrist of the person. In some embodiments, the strap 216 may be sized so as to tit around the person's chest, which may be particularly advantageous in embodiments where the system 200 is configured to track the person's breathing rate by measuring expansion and contraction of the person's chest. On the strap 216 is mounted a housing 218 which houses a carbon dioxide sensor 212 and a heart rate sensor 214. The heart rate sensor 214 may, in some embodiments, be a photoplethysmography sensor or pulse oximeter which requires contact with a person's skin. Of course, other suitable sensors may be used, such as an electrical heart rate monitor. The housing 218 also houses one or more processing devices, one or more memory devices and a wireless communication interface for interfacing with a wireless communication network shown by arrow 230, as well as a power source such as a battery for powering all of the components present within the wearable device 210. The wearable device 210 is therefore able to perform some processing using the one or more processors which are located in the housing 218, but preferentially the wearable device 210 communicates data to the smartphone 220 where a majority of the data processing is performed, as the smartphone 220 is likely to be able to perform faster and more efficient processing of the data In this way, the one or more processing devices on the wearable device 210 can be optimised for efficiency rather than performance, and so the battery life of the wearable device may be extended.

In particular, the wearable device 210 is configured to monitor and measure a concentration of carbon dioxide in air using the carbon dioxide sensor 212, and monitor and measure the person's heart rate using the heart rate sensor 214. The wearable device 210 may then pass these measurements to the smartphone 220 via the communication network indicated by arrow 230, such that the smartphone 220 can quantify an amount of air inhaled by the person that is rebreathed air as set out below. By being provided in part as a wearable device 210, the system 200 is able to sense measure a carbon dioxide concentration in the vicinity of the person, thus providing accurate and personalised air quality monitoring.

In some examples, the carbon dioxide sensor 212 may also be used to determine when the person is indoors or in an enclosed space. For example, the carbon dioxide sensor 212 may periodically or repeatedly measure the carbon dioxide level and the one or more processors on the wearable device 210 (or on the smartphone 220) may compare the sensed carbon dioxide level with a threshold value to determine whether the person is indoors or outdoors. For example, if it is determined that the sensed carbon dioxide concentration is greater than a stored threshold (e.g. 415 ppm), it may be determined that the person is indoors. In another example, the one or more processors may quantify a difference between repeated measurements of the carbon dioxide level, and if the difference is greater than a threshold level it may be determined that the person is indoors. The system 200 may, in certain examples, only proceed with quantifying a fraction of air that is rebreathed air, and an amount of air inhaled by the person that is rebreathed air in response to determining that the person is indoors. This may ensure that the system resources (in particular, energy from a battery power source) are utilised efficiently. The repetition frequency of such measurements to determine whether the user is indoors may be adjusted by a user, for example through a smartphone app.

Adjustment of the time between subsequent measurements may be used to balance responsiveness of the system 200 to when a person goes indoors with power preservation of the battery on the wearable device 210.

The smartphone 220 may be any suitable smartphone, for example an Apple iPhone (trade mark), Samsung Galaxy (trade mark) or the like. In particular, the smartphone 220 may be provided with a dedicated application which is configured for compatibility with the wearable device 210. The smartphone 220 comprises one or more processors and one or more memory devices and a wireless communication interface for interfacing with the wireless communication network shown by arrow 230. The smartphone 220 also comprises an electronic display 222, which may be a touchscreen display, to display a visual representation of a quantified amount of air that is rebreathed air to the person. The person may also input additional data 240 by interacting with the smartphone 200, for example by interacting with the electronic display 222. Such additional data 240 may include physiological characteristics of the person, and/or an indication of a number of other persons in the vicinity of the person. The application may be configured to provide a visual prompt to the user on the electronic display 222, asking them to input certain data. For example, the application may prompt the user to confirm whether they are indoors (e.g. to confirm a determination which has been made based on sensors within the wearable device 210 or the smartphone 220), and/or to enter the number of other people in the vicinity of the user.

When the smartphone 220 has received measurements of the carbon dioxide concentration and the person's heart rate from the wearable device 210, the smartphone 220 executes instructions stored in the one or more memory devices to quantify an amount of air inhaled by the person based on the person's heart rate, quantify a fraction of air that is rebreathed air based on the measure of the carbon dioxide concentration, and quantify an amount of air inhaled by the person that is rebreathed. In particular, the smartphone 220 uses equation (1) given above, where the measured carbon dioxide concentration received from the wearable device 210 is used as the value for the measured carbon dioxide concentration (Cmeas) and reference values stored in the one or more memory devices are used for the reference carbon dioxide concentration and the exhaled carbon dioxide concentration (Crec, and Ceith respectively), in order to quantify the rebreathed fraction of air. If the person has input additional data 240 to indicate the number of other persons in their vicinity, then the smartphone 220 may additionally or alternatively use equation (6) to quantify the fraction of air that is rebreathed air due to other persons in the vicinity.

The additional data 240 may also include the person's gender, such that the smartphone is able to quantify the person's minute ventilation rate (W) using either equation (2) or equation (3) given above, where the measured heart rate received from the wearable device 210 is used as the heart rate (HR). Of course, if the person does not enter such data then equation (4) may be used. This allows the smartphone to quantify an amount of air inhaled by the person based on the heart rate, by quantifying the person's minute ventilation rate. In some examples, the person's lung capacity or tidal volume (that is, the volume of air which is inhaled by the person during a normal breath), or body information allowing calculation or estimation of their lung capacity or tidal volume may also be input as additional information 240. After quantifying the amount of air inhaled by the person and the fraction of air that is rebreathed air, the smartphone 220 is able to quantify an amount of air inhaled by the person that is rebreathed air. When the smartphone 220 has quantified this information, it can be reported to a user via the electronic display 222.

In some embodiments, the breathing rate of the person may be measured directly, for example via a breathing rate sensor. In order to quantify the minute ventilation rate of the person from the breathing rate it is necessary to multiply the measured breathing rate (in breaths per minute) by the tidal volume. It should be noted that the tidal volume is different to the lung capacity as the entire lung volume is not used for typical breathing. The tidal volume for the person may be estimated or may be calculated (for example, calculated on the basis of data defining a physiological characteristic of the person). For example, an average tidal volume of 500 mL may be assumed (see e.g. Beardsell, I et al: MCEM Part A:MCOs, page 33, Royal Society of Medicine Press, 2009), or an estimated value may be retrieved from a database based on a physiological characteristic (e.g. age, weight, gender) of the person. In another example, the person's tidal volume (VI, in mL) may be calculated based on their body weight (W, in Kg) according to the equation (Impact of Height Estimation on Tidal Volume Calculation for Protective Ventilation-A Prospective Observational Study; Andre R. Alexandre et al; Critical Care Explorations; May 2021; 3(5); e0422): VT = (6.2 + 0.414/ (7) where 6.2 mL/Kg is an average tidal volume per kilogram of body weight and 0.5 mL/Kg is the standard deviation. So, for example, the person's tidal volume may be assumed to be 6.2 millilitres per kilogram of body weight.

The smartphone 220 may also provide the system 200 with additional sensing capabilities. For example, the smartphone 220 may comprise sensors which are responsive to atmospheric conditions such as humidity or temperature, or which are responsive to electromagnetic radiation such as visible light of mobile network strength. Such sensors may be used in addition to or as an alternative to the carbon dioxide sensor 212 to determine whether the person is indoors or outdoors. For example, a sensed light intensity, humidity, temperature, and/or mobile network strength may be compared with a threshold value to determine whether the smartphone 220, and hence the person, is indoors or outdoors. The sensed parameters may also be measured repeatedly over time, and changes in the measured values may be used to determine whether the person is indoors or outdoors.

The communication network indicated by arrow 230 may be any suitable wired or wireless communication network. For example, the wearable device 210 may communicate with the smartphone 220 over a universal serial bus (USB) connection, a Bluetooth connection, a Wi-Fi connection, or any other such communication network or protocol. Of course, the wearable device 210 and the smartphone 220 may each be configured to communicate over a plurality of communication networks.

Fig. 3 is a flow diagram showing a method 300 for quantifying a volume of air inhaled by a person that is rebreathed air according to an embodiment of the present invention, and which may be performed by an air quality monitoring system, for example the system 100 shown in Fig. 1 or the system 200 shown in Fig. 2.

In a first step 302, the method 300 measures a carbon dioxide concentration to which the person is exposed. The carbon dioxide concentration is detected by a carbon dioxide sensor, such as a photoacoustic sensor, in a wearable device, for example, and an associated processor may use the sensor in order to measure the carbon dioxide concentration. The measured carbon dioxide value is then used to determine whether the person is indoors at step 304. For example, the measured carbon dioxide value may be compared with a threshold value (e.g. 415 ppm, which may be taken as an average outdoors carbon dioxide concentration) and if the carbon dioxide concentration is greater than this threshold value it may be considered that the person is indoors at the method may continue to step 308 (Yes'). Alternatively, if the measured carbon dioxide level is equal to or lower than the threshold then it may be considered that the person is outdoors such that air quality monitoring is not required, and the method may be paused at step 306 ('No') for a predetermined period of time. When the predetermined period of time has elapsed, the method returns to step 302 and takes a further measurement of the carbon dioxide concentration. As an alternative, or in addition to, comparing the carbon dioxide value with a threshold, step 304 may involve monitoring how the measured carbon dioxide level changes over time. For example, the difference between sequential carbon dioxide readings may be compared with a threshold level change in order to determine whether the person is indoors. For example, a difference between sequential readings which is greater than a threshold change may indicate that the person has moved indoors.

In this way, further processing is only performed when it is determined that a user is likely to be indoors, where air quality monitoring is needed. Steps 302, 304, 306 thereby form a processing loop. This may increase the efficiency of a system on which the method is performed, as system resources are only utilised when required.

When step 304 determines that the person is indoors, processing continues, and a heart rate of the person is measured at step 308. For example, the heart rate of the person may be detected by a heart rate sensor, such as a photoplethysmography sensor in a wearable device, for example. It will be appreciated that, in some embodiments, a breathing rate of the person is measured in addition to or instead of the heart rate at step 308. However, by measuring the heart rate at step 308, the minute ventilation rate may be estimated, for example according to equations (2) and/or (3). In particular, to allow the breathing rate to be quantified, physiological characteristics may be retrieved, for example from a memory device, at step 310.

An amount of air inhaled by the person is quantified at step 312, based on the measured heart rate from step 308. In particular, the minute ventilation rate is quantified, for example according to equations (2) or (3), so an amount of air inhaled by the person can be quantified by determining the relevant time period.

The fraction of air that is rebreathed air is quantified at step 314, based on the carbon dioxide concentration measured at step 302 In other examples, another measurement of the carbon dioxide concentration may be taken, independently of the measurement used to determine whether the person is indoors. For example, step 314 may involve quantifying the rebreathed fraction from equation (1) given above, where the measured carbon dioxide concentration is used as the value for the measured carbon dioxide concentration (Crneas) and reference values stored in the one or more memory devices are used for the reference carbon dioxide concentration and the exhaled carbon dioxide concentration (Cref, and Cexh respectively), in order to quantify the rebreathed fraction of air. In some embodiments of the method, the person may indicate the number of other persons in their vicinity such that equation (6) may be used to quantify the fraction of air that is rebreathed air due to other persons in the vicinity.

An amount of air inhaled by the person that is rebreathed air is quantified at step 316, based on the amount of air inhaled by the person quantified at step 312 and the fraction of air that is rebreathed air quantified at step 316. For example, the amount of rebreathed air inhaled by the person may be quantified as an amount of air per minute, or over any period of time. This information may be displayed to the person, for example on an electronic display as described above with respect to Fig. 2, Figure 4 depicts an example computing system 1000. The following description of the computing system 1000 is provided by way of example only and is not intended to be limiting.

The example computing system 1000 includes a processor 1004 for executing software routines. Although a single processor is shown for the sake of clarity, the computing system 1000 may also include a multi-processor system. The processor 1004 is connected to a communication infrastructure 1006 for communication with other components of the computing system 1000. The communication infrastructure 1006 may include, for example, a communications bus, cross-bar, or network.

The computing system 1000 further includes a main memory 1008, such as a random access memory (RAM), and a secondary memory 1010. The secondary memory 1010 may include, for example, a hard disk drive 1012 and/or a removable storage drive 1014, which may include a floppy disk drive, a magnetic tape drive, an optical disk drive, solid state storage or the like. The removable storage drive 1014 reads from and/or writes to a removable storage unit 1018 in a well-known manner. The removable storage unit 1018 may include a floppy disk, magnetic tape, optical disk, removable solid state storage (e.g. SD card) or the like, which is read by and written to by removable storage drive 1014 As will be appreciated by persons skilled in the relevant art(s), the removable storage unit 1018 includes a computer readable storage medium having stored therein computer executable program code instructions and/or data.

In an alternative implementation, the secondary memory 1010 may additionally or alternatively include other similar means for allowing computer programs or other instructions to be loaded into the computing system 1000. Such means can include, for example, a removable storage unit 1022 and an interface 1020. Examples of a removable storage unit 1022 and interface 1020 include a program cartridge and cartridge interface (such as that found in video game console devices), a removable memory chip (such as an EPROM or PROM) and associated socket, and other removable storage units 1022 and interfaces 1020 which allow software and data to be transferred from the removable storage unit 1022 to the computer system 1000 The computing system 1000 also includes at least one communication interface 1024.

The communication interface 1024 allows software and data to be transferred between computing system 1000 and external devices via a communication path 1026. In various embodiments, the communication interface 1024 permits data to be transferred between the computing system 1000 and a data communication network, such as a public data or private data communication network. The communication interface 1024 may be used to exchange data between a plurality of different computing systems 1000 that together form an interconnected computer network. Examples of a communication interface 1024 can include a modem, a network interface (such as an Ethernet card), a communication port, an antenna with associated circuitry and the like. The communication interface 1024 may be wired or may be wireless. Software and data transferred via the communication interface 1024 are in the form of signals which can be electronic, electromagnetic, optical or other signals capable of being received by communication interface 1024. These signals are provided to the communication interface via the communication path 1026.

As shown in Figure 4, the computing system 1000 further includes a display interface 1002 which performs operations for rendering images to an associated display 1030 and an audio interface 1032 for performing operations for playing audio content via associated speaker(s) 1034.

As used herein, the term "computer program product" may refer, in part, to removable storage unit 1018, removable storage unit 1022, a hard disk installed in hard disk drive 1012, or a carrier wave carrying software over communication path 1026 (wireless link or cable) to communication interface 1024. A computer readable medium can include magnetic media, optical media, or other recordable media, or media that transmits a carrier wave or other signal These computer program products are devices for providing software to the computing system 1000.

The computer programs (also called computer program code) are stored in main memory 1008 and/or secondary memory 1010. Computer programs can also be received via the communication interface 1024. Such computer programs, when executed, enable the computing system 1000 to perform one or more features of embodiments discussed herein. In various embodiments, the computer programs, when executed, enable the processor 1004 to perform features of the above-described embodiments. Accordingly, such computer programs represent controllers of the computer system 1000.

Software may be stored in a computer program product and loaded into the computing system 1000 using the removable storage drive 1014, the hard disk drive 1012, or the interface 1020. Alternatively, the computer program product may be downloaded to the computer system 1000 over the communications path 1026. The software, when executed by the processor 1004, causes the computing system 1000 to perform functions of embodiments described herein.

It is to be understood that the embodiment of Figure 4 is presented merely by way of example. Therefore, in some embodiments one or more features of the computing system 1000 may be omitted. Also, in some embodiments, one or more features of the computing system 1000 may be combined Additionally, in some embodiments, one or more features of the computing system 1000 may be split into one or more component parts It will be appreciated that the elements illustrated in Figure 4 function to provide means for performing the various functions and operations of the computer systems as described in the above embodiments.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word "comprise" and "include", and variations such as "comprises", "comprising", and "including" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent "about,-it will be understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and means for example +1I 0%.

Claims

Claims 1. A system for quantifying an amount of air inhaled by a person that is rebreathed air, the system comprising: a carbon dioxide sensor responsive to carbon dioxide in air; a heart rate sensor or a breathing rate sensor responsive to a person's heart rate or breathing rate respectively; one or more processors, and one or more memory devices storing machine-readable instructions, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to: measure a concentration of carbon dioxide in air using the carbon dioxide senso measure the person's heart rate or breathing rate using the heart rate sensor or the breathing rate sensor respectively, and instruct execution of computational operations to: quantify an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate, quantify a fraction of air that is rebreathed air based on the measure of the concentration of carbon dioxide in the air, and quantify an amount of air inhaled by the person that is rebreathed air based on the quantified amount of air inhaled by the person and the quantified fraction of air that is rebreathed air.
2. The system of claim 1, further comprising an attachment apparatus for attaching one or more of the carbon dioxide sensor, the heart rate sensor, or the breathing rate sensor to the person.
3. The system of claim 1 or claim 2, wherein the system comprises a wireless communication interface for interfacing with a wireless communication network, and the machine-readable instructions are executable by the one or more processors to cause the processors to output, by the wireless communication interface to the wireless communication network: data representing the measure of the person's heart rate or breathing rate and the measure of the concentration of carbon dioxide in air, and the instructions to execute the computational operations.
4. The system of claim 1 or claim 2, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to execute the computational operations.
5. The system of any one of the preceding claims, wherein the machine-readable instructions are executable by the one or more processors to cause the one or more processors to output a representation of the quantified amount of air that is rebreathed air.
6. The system of any one of the preceding claims, comprising an electronic display, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to display on the electronic display a visual representation of the quantified amount of air that is rebreathed air.
7. The system of any one of the preceding claims, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to: measure an atmospheric condition and/or electromagnetic radiation using the carbon dioxide sensor and/or a further sensor, determine whether the measured atmospheric condition and/or electromagnetic radiation is greater or lesser than a reference value, and proceed with the instructing execution of the computational operations in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is one of greater or lesser than the threshold value, else delay the instructing execution of the computational operations in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is the other of greater or lesser than the reference value.
8. The system of any one of claims Ito 6, wherein: the machine-readable instructions are executable by the one or more processors to cause the processors to: measure an atmospheric condition and/or electromagnetic radiation using the carbon dioxide sensor and/or a further sensor, repeatedly measure the atmospheric condition and/or the electromagnetic radiation using the carbon dioxide sensor and/or the further sensor after a period of time has elapsed since the measuring an atmospheric condition and/or electromagnetic radiation, quantify a difference between the measurement of the atmospheric condition and/or the electromagnetic radiation and the repeat measurement of the atmospheric condition and/or the electromagnetic radiation, determine whether the difference between the measurement of the atmospheric condition and/or the electromagnetic radiation and the repeat measurement of the atmospheric condition and/or the electromagnetic radiation is one of greater or lesser than a threshold difference, and proceed with the instructing execution of the computational operations in response to determining that the difference is one of greater or lesser than a threshold difference else delay the instructing execution of the computational operations in response to determining that the difference is the other of greater or lesser than the threshold difference.
The system of any one of claims 1 to 6, wherein: the one or more memory devices store data defining a reference value, the machine-readable instructions are executable by the one or more processors to cause the processors to: determine whether the measured concentration of carbon dioxide in the air is greater or lesser than the reference value; and in response to determining that the measured concentration of carbon dioxide in the air is one of greater or lesser than the reference value, proceed with the instructing execution of the computational operations.
10. The system of claim 9, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to: in response to determining that the measured concentration of carbon dioxide in the air is the other of greater or lesser than the reference value, delay the instructing execution of the computational operations and repeat the measuring a concentration of carbon dioxide in the air using the carbon dioxide sensor after a period of time has elapsed.
11 The system of any one of the preceding claims, wherein the machine-readable instructions are further executable by the one or more processors to cause the processors to instruct retrieval of data defining a physiological characteristic of the person, and the instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate comprises instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate and the physiological characteristic.
12. The system of any one of the preceding claims, wherein the machine-readable instructions are executable by the one or more processors to cause the processors to: obtain an indication of a number of other persons in the vicinity of the person; and instruct the execution of the computational operation to quantify the fraction of air that is rebreathed air based on the measure of the concentration of carbon dioxide in air by the carbon dioxide sensor and based on the indication of the number of other persons in the vicinity.
13. A method for quantifying an amount of air inhaled by a person that is rebreathed air, the method comprising: measuring a concentration of carbon dioxide in air to which the person is exposed using a carbon dioxide monitor, and measuring the person's heart rate or breathing rate using a heart rate monitor or a breathing rate monitor, instructing quantification of: an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate, a fraction of air that is rebreathed air based on a measure of the concentration of carbon dioxide in air by the carbon dioxide monitor, and an amount of air inhaled by the person that is rebreathed air based on the quantified amount of air inhaled by the person and the quantified fraction of air that is rebreathed air.
14. The method of claim 13, further comprising: measuring an atmospheric condition and/or electromagnetic radiation using the carbon dioxide monitor and/or a further monitor, determining whether the measured atmospheric condition and/or electromagnetic radiation is greater or lesser than a reference value, and proceeding with instructing quantification in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is one of greater or lesser than the threshold value, else delaying instructing quantification in response to a determination that the measured atmospheric condition and/or electromagnetic radiation is the other of greater or lesser than the threshold value.
15 The method of claim 13, further comprising: measuring an atmospheric condition and/or electromagnetic radiation using the carbon dioxide monitor and/or a further monitor, repeatedly measuring the atmospheric condition and/or the electromagnetic radiation using the carbon dioxide monitor and/or the further monitor after a period of 30 time has elapsed since the measurement an atmospheric condition and/or electromagnetic radiation, determining whether a difference between the measurement of the atmospheric condition and/or the electromagnetic radiation and the repeat measurement of the atmospheric condition and/or the electromagnetic radiation is one of greater or lesser than a threshold difference, and proceeding with instructing quantification in response to determining that the difference is one of greater or lesser than a threshold difference else delaying instructing quantification in response to determining that the difference measured atmospheric condition and/or electromagnetic radiation is the other of greater or lesser than the threshold difference
16. The method of claim 13, further comprising: determining whether the measured concentration of carbon dioxide in the air is greater or less than a reference value; and in response to determining that the measure concentration of carbon dioxide in the air is one of greater or lesser than the reference value, proceeding with instructing execution of the computational operations.
17. The method of claim 16, further comprising: in response to determining that the measured concentration of carbon dioxide in the air is the other of greater or lesser than the reference value, delaying instructing quantification and repeating the measuring a concentration of carbon dioxide in the air using the carbon dioxide monitor after a period of time has elapsed.
18. The method of any one of claims 13 to 17, further comprising: instructing retrieval of data defining a physiological characteristic of the person, and instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate comprises instructing quantification of an amount of air inhaled by the person based on the measure of the person's heart rate or breathing rate and the physiological characteristic.
19. The method of any one of claims 13 to 18, further comprising: obtaining an indication of a number of other persons in the vicinity of the person; and instructing the quantification of the fraction of air that is rebreathed air based on the measure of the concentration of carbon dioxide in air by the carbon dioxide monitor and based on the indication of the number of other persons in the vicinity.