Portable Air Pollution Sensors and Their Application to Urban Microenvironments


Student thesis: Doctoral Thesis

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Award date2 Sept 2019


Although ambient air quality standards have become more and more stringent in many countries, human exposure to air pollution is still a major public health concern, especially in major urban areas. Conventional air quality monitoring (AQM) is commonly carried out by the government agencies by means of stationary AQM networks. The cost of establishing fixed AQM sites is substantial, not to mention requiring a significant amount of resources for operation and maintenance. A new technological approach is emerging with the recent advances in sensor technologies that makes possible the construction and use of small, low cost sensor system, thus enabling performance monitoring in locations not covered by traditional monitoring networks. This thesis focuses on the development of protocols for the use of portable air pollution sensors and their application in various microenvironments in Hong Kong, with a primary emphasis on traffic-related air pollutants.

First, air pollution in public transport microenvironments with passenger exposure was investigated using a Mobile Exposure Measurement System (MEMS). Transit microenvironments classified as 1) busy and secondary roadside bus stops, 2) open and enclosed transit termini, and 3) above- and under-ground Mass Transit Railway (MTR) platforms were investigated and compared to identify factors that may affect passenger exposure. Busy roadside and enclosed termini exhibited the highest average particle concentrations while the lowest were found on MTR platforms. In-cabin air pollution measurements showed distinct patterns with high black carbon (BC) and high ultrafine particle (UFP) concentrations in diesel bus cabins and high carbon monoxide (CO) in liquefied petroleum gas (LPG) bus (also refers to minibus) cabins suggesting possible self-generated pollution and/or penetration of on-road pollutants to the cabins. The total passenger aggregated exposure (AE) along selected routes reveals that traveled by bus have a higher potential for AE compared to traveled by MTR.

Second, traffic-induced urban air pollution was evaluated using a Mobile Air Sensor Network (MASEN), monitoring on-road pollutant concentrations at a high spatial and temporal resolution. After removing the on-road baseline data, the contributions of local routes to the total emissions in the on-road environment were found to be 49%, 36%, 18.6%, and 18.9% for nitric oxide (NO), nitric dioxide (NO2), CO and particulate matter with diameter less than 2.5 μm (PM2.5), respectively. Moreover, it was found that vehicle-derived PM2.5 might not be the dominant source in on-road environments, while NO is the characteristic pollutant for generated along the bus routes. Nevertheless, the pollutant concentrations along the routes were usually higher than those reported from the official AQM roadside stations. It suggests that the roadside AQM sites may not reflect the actual on-road environment.

Finally, a compact Personal Exposure Kit (PEK) was developed to evaluate Personal Aggregated Exposure (PAE) from time-resolved data for PM2.5 in different microenvironments including office, home, commuting, other indoor activities (other than home and office) and outdoor activities taking place on both weekdays and weekends. The PM2.5 concentrations were found to be the lowest (13.0 μg/m3) in the office microenvironment while the largest were found during outdoor activities (54.4 μg/m3). On average 42% and 81% of the time was spent in the home environment, which contributed 52% and 79% of PAE on weekdays and weekends, suggesting that improving the air quality in homes may reduce the aggregated exposure to PM2.5. It should be noted that concentrations in the indoor and outdoor microenvironments experienced by urban office workers in this study may not be directly comparable with the AQM monitoring data due to different averaging times and monitoring protocols.

    Research areas

  • Air pollution, Microenvironments, Aggregated exposure, Portable sensors