The washout effects of rainfall on atmospheric particulate pollution in two Chinese cities

Understanding meteorological influences on PM<sub>2.5</sub> concentrations across China: a temporal and spatial perspective

“…Instead, the slight precipitation may induce enhanced relative humidity and thus lead to the increase in PM 2.5 concentrations. Meanwhile, the washing-off effect from the same amount of precipitation on PM 2.5 concentrations in Xi'an, a city with higher PM 2.5 concentrations, was lower than that in Guangzhou (Guo et al, 2016), indicating local PM 2.5 concentrations also exerted a key role in the negative effects of precipitation. Meanwhile, temperature can either be negatively correlated with PM 2.5 concentrations by accelerating the flow circulation and promoting the dispersion of PM 2.5 (Li et al, 2015b), or positively correlated with PM 2.5 concentrations through inversion events (Jian et al, 2012).…”

“…Therefore, meteorological means for encouraging strong winds are more likely to reduce PM 2.5 concentrations considerably in North China. Similarly, Luo et al (2017) suggested that only precipitation with a certain magnitude can lead to the washing-off effect of PM 2.5 concentrations, whilst Guo et al (2016) revealed that the variation of PM 2.5 concentrations was more sensitive to the same amount of precipitation in areas with lower PM 2.5 concentrations. Therefore, meteorological means for inducing precipitation are more likely to improve air quality in coastal cities and cities within the Yangtze River Basin, where there is a large amount of precipitation and relatively low PM 2.5 concentrations.…”

“…This may be attributed to the fact that these meteorological factors mainly exert influence on local PM 2.5 concentrations in those cities (seasons) where (when) the general PM 2.5 concentrations are not high. Taking the precipitation as an example, Luo et al (2017) pointed out that there may be thresholds for the negative influences of precipitations on PM 2.5 concentrations and Guo et al (2016) found that the same amount of precipitation led to a weaker washing-off effect in areas with higher PM 2.5 concentrations. Hence, precipitation mainly exerts a dominant influence on local PM 2.5 concentrations in winter for the Yangtze River Basin or coastal cities, where the amount of precipitation is large and the PM 2.5 concentration is low, whilst precipitation exerts a limited role in northern China, where the amount of precipitation is small and the PM 2.5 concentration is high.…”

“…Meanwhile, wind speed exerted a major influence on PM 2.5 concentrations in Beijing in winter. Through experiments, Guo et al (2016) found that the influence of precipitation on PM 2.5 concentrations in Xi'an was weaker than that in Guangzhou. H. quantified the correlations between meteorological factors and the main airborne pollutants in three megacities, Beijing, Shanghai and Guangzhou, and pointed out that the influences of meteorological factors on the formation and concentrations of PM 2.5 varied significantly across seasons and geographical locations.…”

Analysis of Aerosol Composition and Assessment of Tunnel Washing Performance within a Mass Rapid Transit System in Taiwan

“…Therefore, the reduction or removal of PM in the tunnel can improve the air quality of MRT stations. Previous studies (Hu et al, 2006;Feng et al, 2012;Guo et al, 2016) have reported that the time and amount of rainfall had different scavenging rates (up to 80%) for PM of different sizes in the surrounding air, because many soluble salts are found in the surrounding air. Therefore, we evaluated whether the use of water columns to wash the inner walls of the tunnels in an MRT system can reduce the PM concentration.…”