A WRF-CMAQ modeling of atmospheric peroxyacetyl nitrate and source apportionment in Central China

Atmospheric peroxyacetyl nitrate (PAN), as an essential constituent in the photochemical smog, is formed from photochemical reactions between volatile organic compounds (VOCs) and NOx. However, limited regional studies on distribution, formation and sources of PAN restrict the further understanding of the atmospheric behavior and environmental significance of PAN. In this study, the variation characteristics of PAN and the influencing factors to PAN concentrations were investigated using the WRF-CMAQ model simulation in the central China during July 2019. The results showed that the monthly mean concentration of PAN in the near-surface layer was 0.4 ppbv and increased with the height rising, accompanied by strong intra-day variation. The process analysis suggested that the removal was mainly controlled by dry deposition (57 %), followed by the gas-phase chemistry (43 %) which was mainly attributed to the thermal decomposition. Based on the sensitivity simulation, PAN concentrations decreased effectively in most of the simulated regions when precursors of VOCs and NOx emissions were reduced, and PAN concentrations were more sensitive to VOCs emissions than NOx emissions. The reduction of NOx and VOCs could lead to enhanced atmospheric oxidation in east-central region, which in turn hindered the decrease of PAN concentrations. During the simulation period, we found that emissions from industry and transportation sectors had the greatest impact on PAN concentrations in the central China, with contributions of 39 %-49 % and 33 %-41 %, respectively.