Real-time monitoring of personal exposures to carbon dioxide

Abstract

Elevated indoor CO2 levels are indicative of insufficient ventilation in occupied spaces and correlate with elevated concentrations of pollutants of indoor origin. Adverse health and wellbeing outcomes associated with elevated indoor CO2 levels are based on CO2 as a proxy, although some emerging evidence suggests CO2 itself may impact human cognition. Using portable monitors, we conducted an exposure study with 16 subjects in Singapore to understand the levels, dynamics and influencing factors of personal exposure to CO2. Participants carried a CO2 monitor continuously for 7-day periods recording their exposure levels at 1-min intervals. A recall diary was maintained of time-microenvironment-activity budget. We found that the mode of bedroom ventilation was a major determinant of CO2 exposure. Approximately half of the participants slept in bedrooms employing ductless split air-conditioners (group "AC"); half slept in bedrooms naturally ventilated through operable windows (group "NV"). Median CO2 exposure levels for AC vs. NV groups are significantly different (̃ = 650 ppm vs. ̃ = 550 ppm, p < 0.001). Mean daily integrated exposures for group AC were statistically higher than for group NV: 22,800 ppm h/d vs. 16,000 ppm h/d (p < 0.005). Exposure events associated with potential adverse cognitive implications (duration > 2.5 h, average CO2 mixing ratio > 1000 ppm) occurred, on average, at frequencies of 0.5 d -1 across all participants, 0.6 d -1 for AC participants and 0.2 d -1 for NV participants. The majority of such events occurred in the home (86%), followed by work (9%) and transit (3%).

Longitudinal assessment of thermal and perceived air quality acceptability in relation to temperature, humidity, and CO2 exposure in Singapore

“…The AC group who slept with air-conditioning operating tended to be exposed to lower air temperatures and relative humidities, but higher CO 2 levels than the NV group, since most of the participants spent 50% or more of their time at home. In addition, average daily CO 2 exposure for the AC group was substantially higher than the recorded median CO 2 mixing ratio during the experiment; the likely explanation is that the highest home CO 2 levels for the AC group occurred while sleeping [32]. Regarding acceptability responses, the MX group was observed to record higher TA and PAQA than the other two groups.…”

“…The 90 th percentile level of CO 2 in transport environments is particularly striking; it is likely associated with a generally high occupant density especially during commute times on buses and in the rail mass rapid transit system (MRT). A detailed analysis of the CO 2 levels encountered and their potential significance has been reported by Gall et al [32]. Table 1 also summarizes the surveyed subjects' assessment of thermal and perceived air quality acceptable/unacceptable choice.…”

“…Detailed information about the experimental design and results for carbon dioxide exposures were previously reported [32]. Here, we focus on the instantaneous assessments by participants of the thermal and perceived air quality acceptability of the spaces they occupied.…”

Miniaturized Monitors for Assessment of Exposure to Air Pollutants: A Review

“…Sensor characteristics are reported in Table 3 , while a study summary is reported in the supplemental material (Tables S1 and S2) . Most of the selected papers were related to the monitoring of CO [ 5 , 6 , 9 , 29 , 31 , 36 , 38 , 39 ], CO 2 [ 5 , 9 , 29 , 40 , 41 , 42 , 43 , 44 ], O 3 [ 3 , 5 , 9 , 29 , 31 , 36 ] and NO 2 [ 6 , 9 , 29 , 31 , 38 ], even though other pollutants were sometimes considered, such as NO [ 5 , 6 , 29 ], SO 2 [ 29 , 38 ]; VOC [ 45 ], and hydrocarbons and acids [ 46 ]. Several studies reported results regarding wearable sensors provided to pedestrians.…”

Window/door opening-mediated bedroom ventilation and its impact on sleep quality of healthy, young adults

“…The importance of bedroom ventilation on overall exposure to CO 2 has been highlighted in some recent studies. The study by Gall et al assessed CO 2 exposure of participants over their entire day and found that occupants in bedrooms with split air conditioners (AC) faced greater mean daily integrated CO 2 exposures and frequency of exposure to critical levels of CO 2 , as compared to occupants in naturally ventilated (NV) bedrooms. In a similar study, it was found that bedrooms with natural ventilation provided better sleeping condition than those with split ACs, even though the thermal conditions of bedrooms with AC stayed within recommended limits while in NV bedrooms, the limits were routinely exceeded.…”