Characteristics of Chemical Speciation in PM₁ in Six Representative Regions in China

A better knowledge of aerosol properties is of great significance for elucidating the complex mechanisms behind frequently occurring haze pollution events. In this study, we examine the temporal and spatial variations in both PM₁ and its major chemical constituents using three-year field measurements that were collected in six representative regions in China between 2012 and 2014. Our results show that both PM₁ and its chemical compositions varied significantly in space and time, with high PM₁ loadings mainly observed in the winter. By comparing chemical constituents between clean and polluted episodes, we find that the elevated PM₁ mass concentration during pollution events should be largely attributable to significant increases in organic matter (OM) and inorganic aerosols like sulfate, nitrate, and ammonium (SNA), indicative of the critical role of primary emissions and secondary aerosols in elevating PM₁ pollution levels. The ratios of PM₁/PM_2.5 are found to be generally high in Shanghai and Guangzhou, while relatively low ratios are seen in Xi'an and Chengdu, indicating anthropogenic emissions were more likely to accumulate in forms of finer particles. With respect to the relative importance of chemical components and meteorological factors quantified via statistical modeling practices, we find that primary emissions and secondary aerosols were the two leading factors contributing to PM₁ variations, though meteorological factors also played important roles in regulating the dispersion of atmospheric PM.