Use of the PSCF method to analyze the variations of potential sources and transports of NO2, SO2, and HCHO observed by MAX-DOAS in Nanjing, China during 2019

Abstract Although the government of Nanjing implemented the more stringent atmospheric control measures during the second half of 2019, compared with the same period in 2018, the air pollution has increased unexpectedly, such as the O3 pollution and the acid rain. In this study, therefore, we performed observations of the vertical structures of the precursors (NO2, SO2, and HCHO) that caused the pollutions in Nanjing using the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument during the daytime of 2019. The concentration of NO2 was found to be concentrated primarily within 200 m of the surface and decayed sharply with height, although the profiles of SO2 and HCHO could extend to higher altitudes than NO2. Then, the potential source contribution function (PSCF) was used to analyze the source distributions in different atmospheric layers of Nanjing's pollutants during different seasons. The results reveal that the downtown and north of Nanjing with the WPSCF is greater than 0.6 constitute the most important potential source areas. Moreover, potential sources in south-central Jiangsu Province (in the summer and autumn) and east-central Anhui Province (in the winter) are also non-negligible (0.4 0.5) than transports in the lower layer (0.3