Understanding summertime H2O2 chemistry in the North China Plain through observations and modeling studies

Abstract

Hydrogen peroxide (H2O2) is a key atmospheric oxidant, crucial for oxidation capacity and sulfate production. However, its chemistry remains understudied compared to ozone (O3), limiting our understanding of photochemical pollution. In summer 2016, atmospheric peroxides and trace gases were measured at a rural site in the North China Plain. H2O2 was the dominant peroxide (0.62 ± 0.80 ppb), constituting 69 % of total peroxides. It exhibited diurnal variation similar to peroxyacetyl nitrate (PAN) and O3, indicating photochemical production. The O3/H2O2 ratio was higher on high-particle days, suggesting that H2O2 uptake by particles reduces its concentration. A box model with default gas-phase chemistry overestimated H2O2 by a factor of 2.7, and including particle uptake of H2O2 (uptake coefficient of 6 × 10-4) improved agreement with observations, although we note that this value carries some uncertainty related to the assumed HO2 uptake coefficient. HO2 recombination contributed 91 % of H2O2 production, with a peak rate of 1 ppb h-1. Major removal pathways included particle uptake (69 %), dry deposition (25 %), OH reaction (4 %), and photolysis (2 %). Relative incremental reactivity (RIR) analysis showed that reducing NOx, PM2.5, and alkanes increased H2O2, while reducing alkenes, aromatics, CO, and HONO decreased it, with alkenes having the strongest effect. H2O2/NOz ratios (>0.15 in 82 % of cases) indicated that O3 formation was in a transition and NOx-sensitive regime, emphasizing the need for further volatile organic compound (VOC) and NOx reductions to mitigate both H2O2 and O3 pollution. These findings improve our understanding of H2O2 chemistry and provide insights into the mitigation of photochemical pollution in rural North China.