Chemical characteristics, sources and evolution processes of fine particles in Lin'an, Yangtze River Delta, China

In this study, daily PM_2.5 mass and chemical composition were measure in Lin'an Reginal Background Station, Yangzte River Delta, from March 1, 2018, to February 28, 2019. Organic matter (OM) was found to be the most dominant component in four seasons. The proportions of nitrate in PM_2.5 presented dramatically lowest in warm seasons but highest in winter, indicating that NO₃^- was maily driven by thermodynamics. Regional transportation in winter plays a strong impact on PM_2.5 concentration, which showed the highest average mass of 60.1 μg m^-3. Sulfate occupied a significant portion of PM_2.5 in summer (19%), followed by spring (17%), fall (15%), and winter (12%), respectively, suggesting photochemical processes may play a dominant role in the sulfate formation. Secondary inorganic aerosol (SIA) was the dominant component (70%) in the highest polluted periods (PM_2.5 > 75 μg m^-3), whereas OM decreased into the lowest fraction (22%) of PM_2.5. Nitrate was the most important component in SIA in the highest polluted periods with regarding winter. Source apportionment results shown that winter haze was likely strongly dominated by SIA, which was mainly affected by air masses from the North China Plain and Shang-Hangzhou direction. PM_2.5 is known to play an important role in sunlight absorption and reversing to human health, continuous observation on PM_2.5 species in a background site can help us to evaluate the control policy, and promote our insights to lifetime, formation pathways, health effects of PM_2.5.