[Physiochemical Properties of the Aerosol Particles and Their Impacts on Secondary Aerosol Formation at the Background Site of the Yangtze River Delta].

The study of the sources, compositions, and formation mechanisms of pollutants at the background site is crucial for the understanding of episodic events in the Yangtze River Delta (YRD). Secondary species are major components of PM particles. In this work, the compositions and concentrations of organic matter and secondary organic aerosol (SOA) at a background site of the YRD region were determined. The acidity and liquid water content of aerosol particles were modeled to investigate the impact of the physicochemical properties of aerosol particles on the formation of secondary species. The annual mean PM concentration in Chunan is 33 μg·m, with major contributions from inorganic sulfate (19%), nitrate (15%), ammonium (12%), and organic matter (19%). Nitrate is mainly locally formed, while sulfate is more affected by regional transport, except in winter. We found that the particles at the background site of the YRD have a high acidity and no seasonal variation was observed. The SOA formation at the background site of the YRD is enhanced by the liquid water content of the aerosol in spring, while it is more affected by the concentration of the oxidant, that is, O, in summer. The contribution of SOA to PM in summer is as high as 40%.