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
3.3×10-4 to 1.8×10-2 s−1 with
campaign-averaged values of 27.5±9.7, 2.2±2.6 and 1.2±1.7×10-3 s−1 (± standard
deviation), respectively. NOx (NO+NO2) 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 4.5×108 moleculescm-3s-1, with a campaign-averaged value of
7.8×107 moleculescm-3s-1 dominated by OH
(7.7×107 moleculescm-3s-1, 98.2 %), O3
(1.2×106 moleculescm-3s-1, 1.5 %) and NO3
(1.8×105 moleculescm-3s-1, 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 reactivity and AOC.
Summertime fine particulate nitrate pollution in the North China Plain: Increasing
trends, formation mechanisms, and implications for control policy
