Trace Gases over Land and Ocean Surfaces of China: Hotspots, Trends, and Source Contributions

Trace gases in the atmosphere (NO2: nitrogen dioxide; SO2: sulfur dioxide) have a major impact on both local and global air quality, human health, climate and ecological conditions. Therefore, the present study investigated 16 years (2005- 2020) of Ozone Monitoring Instrument (OMI) based NO2 and SO2 in Dobson unit (DU) spatiotemporal distributions and variability, SO2/NO2 ratio, trends, and potential source contribution function (PSCF) across ocean and land areas of Jiangsu Province, China. Results demonstrated higher NO2 and SO2 concentrations (DU) over land (NO2: 0.58 and SO2: 0.56) than in the ocean (NO2: 0.30 and SO2: 0.38) due to more concentrated anthropogenic activities on land surfaces. There were significant seasonal variations in NO2 and SO2, with winter being the highest and summer being the lowest. The SO2/NO2 ratio shows land and ocean pollution is caused by NO2 and SO2 emissions from ships and industrial processes. Furthermore, OMI-based trace gases and anthropogenic emissions showed a good correlation (NO2 vs NOx = 0.626 and SO2 vs SO2 emission = 0.871) across land surfaces than the ocean (NO2 vs NOx = 0.366). NO2 and SO2 levels over land surfaces decreased significantly (at a 95% confidence level) compared to the ocean on annual and seasonal scales, which is attributed to a decrease in NOx and SO2 emissions. Furthermore, PSCF analysis shows that local sources have a greater impact on air quality than long-distance sources over land and ocean. It is concluded from this study that Chinese air pollution control policies achieved a satisfactory improvement in Jiangsu's air quality by reducing NO2 and SO2. It is therefore recommended to continue or extend these policies in the future to improve China's air quality, which will benefits its citizens.