Temporal and spatial analyses of particulate matter (PM10 and PM2.5) and its relationship with meteorological parameters over an urban city in northeast China

Temporal and spatial characteristics of atmospheric particulate matter (PM10 and PM2.5) and its relationship with meteorology over Shenyang, a city in northeast China, were statistically analyzed using hourly and daily averaged PM mass concentrations measured at 11 locations and surface meteorological parameters, from January 2014 to May 2016. Using averaged data from 11 stations in Shenyang, it was found that the monthly mean PM2.5 mass concentrations were higher in winter (97.2 ± 11.2 μg m− 3) and autumn (85.5 ± 42.9 μg m− 3), and lower in spring (62.0 ± 14.0 μg m− 3) and summer (42.5 ± 8.4 μg m− 3), similar to the seasonal variation in PM10 concentrations. The monthly ratios of PM2.5/PM10 ranged from 0.41 to 0.87, and were larger in autumn and winter but lowest in spring due to dust activities. PM pollution was concentrated mainly in the central, northern, and western areas of Shenyang in most seasons mainly due to anthropogenic activities such as traffic and residential emission and construction activity as well as natural dust emission. PM concentrations observed over different areas in all seasons generally exhibited two peaks, at 08:00-10:00 local time (LT) and 21:00-23:00 LT, with the exception of PM2.5 in summer, which showed only one peak during the daytime. In addition, PM10 concentrations peaked around 14:00 LT during spring in the western area of Shenyang because of strong thermal and dynamic turbulence, resulting in elevated dust emissions from adjacent dust sources. The relationship between daily PM concentrations and meteorological parameters showed both seasonal and annual variation. Overall, both PM2.5 and PM10 concentrations were negatively correlated with atmospheric visibility, with correlation coefficients (R) of 0.71 and 0.56, respectively. In most seasons, PM concentrations also exhibited negative correlations with wind speed, but showed positive correlations with air pressure, air temperature, and relative humidity. Strong wind speed favored the dispersion of PM pollution, but also aided the release of coarse dust particles in spring. High air pressure and downdrafts restrained the upward movement of atmospheric PM, resulting in an accumulation of particles in the boundary layer. High air temperature favored the transformation of secondary particles through photochemical processes in summer, but also resulted in efficient vertical dispersion of pollutants in autumn and winter, leading to an inverse relationship between temperature and PM concentrations. Large relative humidity usually caused increases in PM concentrations due to the hygroscopic effect of aerosols, but not for PM10 in spring and summer, mainly due to the suppression of dust emissions under wet air conditions in spring and the effects of wet scavenging under high summer rainfall.