Variations of the urban PM chemical components and corresponding light extinction for three heating seasons in the Guanzhong Plain, China.

In order to investigate the variations of PM (particulate matter with an aerodynamic diameter less than 2.5 μm) chemical components responding to the pollution control strategy and their effect on light extinction (b) in the Guanzhong Plain (GZP), the comparisons of urban atmospheric chemical components during the heating seasons were extensively conducted for three years. The average concentration of PM decreased significantly from 117.9 ± 57.3 μg m in the heating season 1 (HS1) to 53.5 ± 31.3 μg m in the heating season 3 (HS3), which implied that the effective strategies were implemented in recent years. The greatest contribution to PM (∼30%) was from Organic matter (OM). The heightened contributions of the secondary inorganic ions (SNA, including NO, SO, and NH) to PM were observed with the values of 34% (HS1), 41% (HS2), and 42% (HS3), respectively. The increased percentages of NO contributions indicated that the emission of NOx should be received special attention in the GZP. The comparison of PM chemical compositions and implications across major regions of China and the globe were investigated. NHNO was the most important contributor to b in three heating seasons. The average b was decreased from 694.3 ± 399.1 Mm (HS1) to 359.3 ± 202.3 Mm (HS3). PM had a threshold concentration of 75 μg m, 64 μg m, and 57 μg m corresponding to the visual range (VR) < 10 km in HS1, HS2, and HS3, respectively. The enhanced impacts of the oxidant on PM and O were observed based on the long-term variations in PM and OX (Oxidant, the sum of O and NO mixing ratios) over the five heating seasons and PM and O over six summers from 2016 to 2021. The importance of coordinated control of PM and O was also investigated in the GZP.