Abstract
Aerosol pollution elicits considerable public concern due to the adverse influence on air quality, climate change, and human health. Outside of emissions, haze formation is closely related to meteorological conditions, especially relative humidity (RH). Partly due to insufficient investigations on the aerosol hygroscopicity, the accuracy of pollution prediction in Central China is limited. In this study, taking Wuhan as a sample city, we investigated the response of aerosol pollution to RH during wintertime based on in-situ measurements. The results show that, aerosol pollution in Wuhan is dominated by PM2.5 (aerodynamic particle size not larger than 2.5 μm) on wet days (RH ≥ 60%), with the averaged mass fraction of 0.62 for PM10. Based on the RH dependence of aerosol light scattering (f (RH)), aerosol hygroscopicity was evaluated and shows the high dependence on the particle size distribution and chemical compositions. f (RH = 80%) in Wuhan was 2.18 (±0.73), which is comparable to that measured in the Pearl River Delta and Yangtze River Delta regions for urban aerosols, and generally greater than values in Beijing. Ammonium (NH4+), sulfate (SO42−), and nitrate (NO3−) were enhanced by approximately 2.5-, 2-, and 1.5-fold respectively under wet conditions, and the ammonia-rich conditions in wintertime efficiently promoted the formation of SO42− and NO3−, especially at high RH. These secondary ions play an important role in aggravating the pollution level and aerosol light scattering. This study has important implications for understanding the roles of RH in aerosol pollution aggravation over Central China, and the fitted equation between f (RH) and RH may be helpful for pollution forecasting in this region.
Highlights
Atmospheric aerosols, consisting of large amounts of solid and liquid particles, could directly or indirectly affect the climate system [1,2,3,4]
Compared with dry conditions (RH ≤ 40%), the average concentration of PM10 only increased by 14% on wet days (RH ≥ 60%), the mean contents of PM1 and PM2.5 almost doubled, which resulted in a remarkable increase in the proportion of fine particles, with the ratio of PM2.5 /PM10 increasing from 0.38 to 0.62 (Table 1)
Quantification of aerosol scattering hygroscopic growth is critical for determining the response of aerosol optical properties on various ambient relative humidity (RH) and modeling the aerosol direct radiative effects
Summary
Atmospheric aerosols, consisting of large amounts of solid and liquid particles, could directly or indirectly affect the climate system [1,2,3,4]. The Intergovernmental Panel on Climate Change (IPCC). Reports that aerosols are consistently the leading contributors to the uncertainty of global climate change [5,6]. Numerous epidemiological studies have indicated that the suspended particles in the atmosphere, especially those with an aerodynamic diameter not larger than 2.5 μm (PM2.5 ), would produce serious adverse effects on human bodies, increasing deaths from cardiovascular and respiratory diseases and even lung cancer [7,8]. Public Health 2019, 16, 4422; doi:10.3390/ijerph16224422 www.mdpi.com/journal/ijerph
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