Comparison of PM2.5 Exposure in Hazy and Non-Hazy Days in Nanjing, China

ABSTRACT

Fine particulate matter (PM_2.5), levels of which are about 6 times the 2014 WHO air quality guidelines for 190 cities in China, has been found to be associated with various adverse health outcomes. In this study, personal PM_2.5 exposures were monitored along a fixed routine that included 19 types of non-residential micro-environments (MEs) on 4 hazy days (ambient PM_2.5 292 ± 70 µg m^–3) and 2 non-hazy days (55 ± 16 µg m^–3) in Nanjing, China using miniaturized real-time portable particulate sensors that also collect integrated filters of PM_2.5 (MicroPEMs, Research Triangle Institute (RTI), NC). Gravimetric correction is necessary for nephelometer devices in calculating real-time PM levels. During both hazy and non-hazy days, personal PM_2.5 levels were generally higher in MEs with noticeable PM_2.5 sources than MEs serving as receptor sites, higher in open MEs than indoor MEs, and higher in densely populated MEs than MEs with few people. Personal PM_2.5 levels measured during hazy and non-hazy days were 242 ± 91 µg m^–3 and 103 ± 147 µg m^–3, respectively. The ratio of personal exposure to ambient PM_2.5 levels (r_p/a) was less than 1.0 and less variable on hazy days (0.85 ± 0.31); while it was larger than 1.0 and more variable on non-hazy days (1.71 ± 1.93), confirming the importance of local sources other than ambient during non-hazy days. Air handling methods (e.g., ventilation/filtration) impacted personal exposures in enclosed locations on both types of days. Street food vendors with cooking emissions were MEs with the highest personal PM_2.5 levels while subway cars in Nanjing were relatively clean due to good air filtration on both hazy and non-hazy days. In summary, on hazy days, personal exposure was mainly affected by the regional ambient levels, while on non-hazy days, local sources together with ambient levels determined personal exposure levels.