Characterization of aerosol composition and sources in a polluted city in Central China

Air pollution problem in megacities in China has been significantly improved as annual average PM_2.5 in 2019 in Beijing was 42 µg/m³. But is still a serious problem in many smaller cities. Sanmenxia is located in the Fen-Wei Plain, close to China's largest coal base. The annual average PM_2.5 of Sanmenxia decreased from 72 µg/m³ in 2015 to 59 µg/m³ in 2019. The highly concentrated industries, especially coal industries, heavy traffic, and the typical terrain that it locates nearby the gorge of the Yellow river, make Sanmenxia a highly polluted city. The highest average PM_2.5 was ~100 µg/m³ in winter. Non-refractory PM₁ (NR-PM₁) species including organic aerosol (Org), sulfate (SO₄), nitrate (NO₃), ammonium (NH₄) and chloride (Chl) were measured at Sanmenxia Environmental Protection Bureau (34.794°N,111.171°E) by the ACSM at a time resolution of ~5 min from December 21, 2018 to January 21, 2019. High time resolution of online meteorological variables, as well as precursor gases, OC/EC, and trace elements were also collected at the site, aiming to characterize the pollution sources and evolution mechanisms of aerosol chemical composition. A long haze episode lasted for 16 days was observed with NR-PM₁ = 76±33 µg/m³, PM_2.5 = 180±89 µg/m³. During this episode, the primary species, nitrate accounted for 32% of NR-PM₁ due to high emission of NOx. Positive matrix factorization (PMF) analysis indicates that industrial emission, coal combustion, traffic emission, and secondary species (sulfate + nitrate + ammonium + secondary organic aerosol) were the major sources of pollution. The diurnal variations of pollutants in Sanmenxia were affected significantly by the vertical movement of air flows, but were not sensitive to the regional transport.