1. Current challenges of improving visibility due to increasing nitrate fraction in PM2.5 during the haze days in Beijing, China.
- Author
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Hu, Shuya, Zhao, Gang, Tan, Tianyi, Li, Chengcai, Zong, Taomou, Xu, Nan, Zhu, Wenfei, and Hu, Min
- Subjects
HAZE ,AIR pollution ,NITRATES ,EMISSION control ,AIR quality ,EMISSION inventories ,AIR pollutants - Abstract
The annual mean PM 2.5 mass concentration has decreased because of the stringent emission controls implemented in Beijing, China in recent years, whereas the nitrate NO 3 – mass fraction in PM 2.5 increases gradually. Low-visibility events occur frequently even though PM 2.5 pollution has been mitigated significantly, with the daily mean PM 2.5 mass concentration mostly less than 75 μg/m
3 . In this study, the non-linear relationship was analyzed between atmospheric visibility and PM 2.5 based on chemical composition from a two-year field observation. Our results showed that NO 3 – became the main constituent of PM 2.5 , especially during the haze pollution episodes. A localized parameterization scheme was proposed between the atmospheric extinction coefficient (σ ext) and major chemical constituents of PM 2.5 by multiple linear regression (MLR). The contribution of NO 3 – to σ ext increased with increasing air pollution, and NO 3 – became the most important contributor for PM 2.5 above 75 μg/m3 . The visibility decreased with increasing NO 3 – mass fraction for the same PM 2.5 mass concentration when PM 2.5 was above 20 μg/m3 . The hygroscopicity of PM 2.5 increased with increasing mass fraction of hygroscopic NO 3 –. These results stressed the importance of reducing particulate NO 3 – and its precursors (for instance, NH 3) through effective emission control measures as well as the tightening of PM 2.5 standards to further improve air quality and visibility in Beijing. [Display omitted] • Nitrate accounted for the largest mass fraction in PM 2.5 during pollution episodes. • Nitrate contributed mostly to visibility impairment during the haze days. • Visibility degraded significantly with increasing nitrate fraction in PM 2.5. [ABSTRACT FROM AUTHOR]- Published
- 2021
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