Contrasting chemical characteristics and secondary formation of PM2.5 from mountain and urban sites in central China

The vertical distribution of aerosol is critical to understand the effect of aerosol on climate. This work explored chemical characteristics of PM 2.5 at three urban and one mountain sites in Shiyan located in central China. Annual PM 2.5 mass concentrations at the mountain site were 70% of urban levels. The total of sulfate, nitrate, and ammonium (SNA) dominated PM 2.5 , showing higher proportion (49.3%) at mountain site. SNA shows the homogeneous vertical distribution in spring, summer, and autumn with coefficient of divergences below 0.2, whereas most of components were more abundant at urban sites in winter. Higher nitrogen oxidation ratio (0.27) and ratio of secondary organic carbon to organic carbon (0.65) indicated that the aerosol in mountainous atmosphere exhibited a greater degree of aging compared to that at urban sites. These findings enhance our understanding of the vertical distribution of PM 2.5 composition and provide a scientific foundation for regional atmospheric pollution control.