Atmospheric reactivity and oxidation capacity during summer at a suburban site between Beijing and Tianjin

Abstract

Hydroxyl (OH) radicals, nitrate (NO3) radicals and ozone (O3) play central roles in the troposphere because they control the lifetimes of many trace gases that result from anthropogenic and biogenic origins. To estimate the air chemistry, the atmospheric reactivity and oxidation capacity were comprehensively analyzed based on a parameterization method at a suburban site in Xianghe in the North China Plain from 6 July 2018 to 6 August 2018. The total OH, NO3 and O3 reactivities at the site varied from 9.2 to 69.6, 0.7 to 27.5 and 3:3104 to 1:8102 s1 with campaign-Averaged values of 27:59:7, 2:22:6 and 1:21:7103 s1 (standard deviation), respectively. NOx (NOCNO2) was by far the main contributor to the reactivities of the three oxidants, with average values of 43 % 99 %. Alkenes dominated the OH, NO3 and O3 reactivities towards total nonmethane volatile organic compounds (NMVOCs), accounting for 42.9 %, 77.8% and 94.0 %, respectively. The total OH, NO3 and O3 reactivities displayed similar diurnal variations with the lowest values during the afternoon but the highest values during rush hours, and the diurnal profile of NOx appears to be the major driver for the diurnal profiles of the reactivities of the three oxidants. A box model (a model to Simulate the concentrations of Organic vapors, Sulfuric Acid and Aerosols; SOSAA) derived from a column chemical transport model was used to simulate OH and NO3 concentrations during the observation period. The calculated atmospheric oxidation capacity (AOC) reached 4:5108 moleculescm3 s1, with a campaign-Averaged value of 7:8107 moleculescm3 s1 dominated by OH (7:7107 moleculescm3 s1, 98.2 %), O3 (1:2106 moleculescm3 s1, 1.5 %) and NO3 (1:8 105 moleculescm3 s1, 0.3 %). Overall, the integration of OH, NO3 and O3 reactivities analysis could provide useful insights for NMVOC pollution control in the North China Plain. We suggest that further studies, especially direct observations of OH and NO3 radical concentrations and their reactivities, are required to better understand trace gas reactivityand AOC.