A typical multi-day ozone (O₃) pollution event was chosen to explore the atmospheric oxidation capacity (AOC), OH reactivity, radical chemistry, and O₃ pollution mechanism in a coastal city of southeastern China, with an observation-based model coupled to the Master Chemical Mechanism (OBM-MCM). The hydroxyl radical (OH) was the predominant oxidant (90 ± 25 %) for daytime AOC, while the NO₃ radical played an important role in AOC during the nighttime (72 ± 9 %). Oxygenated volatile organic compounds (OVOCs; 30 ± 8 %), NO₂ (29 ± 8 %), and CO (25 ± 5 %) were the dominant contributors to OH reactivity, accelerating the production of O₃ and recycling of RO_x radicals (RO_x = OH + HO₂ + RO₂). Photolysis of nitrous acid (HONO, 33 ± 14 %), O₃ (25 ± 13 %), formaldehyde (HCHO, 20 ± 5 %), and other OVOCs (17 ± 2 %) was a major RO_x source, which played an initiation role in atmospheric oxidation processes. Combined with regional transport analysis, the reasons for this O₃ episode were the accumulation of local photochemical production and regional transport. The results of sensitivity analysis showed that volatile organic compounds (VOCs) were the limiting factor of radical recycling and O₃ formation, and the 5 % reduction of O₃ would be achieved by decreasing 20 % anthropogenic VOCs. Controlling emissions of aromatics, alkenes, and alkanes with ≥4 carbons was beneficial for ozone pollution mitigation. The findings of this study provide significant guidance for emission reduction and regional collaboration for future photochemical pollution control in the relatively clean coastal cities of China and similar countries.

A series of CuSO₄/TiO₂ binary oxide catalysts with different CuSO₄ loadings (0–20 wt%) were prepared by a facile solid state impregnation protocol.

Because nitrous acid (HONO) photolysis is a key source of hydroxyl (OH) radicals, identifying the atmospheric sources of HONO is essential to enhance the understanding of atmospheric chemistry processes and improve the accuracy of simulation models. We performed seasonal field observations of HONO in a coastal city of southeastern China, along with measurements of trace gases, aerosol compositions, photolysis rate constants (J), and meteorological parameters. The results showed that the average observed concentration of HONO was 0.54 ± 0.47 ppb. Vehicle exhaust emissions contributed an average of 1.45 % to HONO, higher than the values found in most other studies, suggesting an influence from diesel vehicle emissions. The mean conversion frequency of NO₂ to HONO in the nighttime was the highest in summer due to water droplets evaporating under high-temperature conditions. Based on a budget analysis, the rate of emission from unknown sources (R_unknown) was highest around midday, with values of 4.51 ppb h⁻¹ in summer, 3.51 ppb h⁻¹ in spring, 3.28 ppb h⁻¹ in autumn, and 2.08 ppb h⁻¹ in winter. Unknown sources made up the largest proportion of all sources in summer (81.25 %), autumn (73.99 %), spring (70.87 %), and winter (59.28 %). The photolysis of particulate nitrate was probably a source in spring and summer while the conversion from NO₂ to HONO on BC enhanced by light was perhaps a source in autumn and winter. The variation of HONO at night can be exactly simulated based on the HONO $/$ NO_x ratio, while the J(NO${}_{\mathrm{3}}^{-}$ _R) × pNO${}_{\mathrm{3}}^{-}$ should be considered for daytime simulations in summer and autumn, or $\mathrm{1}/\mathrm{4}\times$ (J(NO${}_{\mathrm{3}}^{-}$ _R) × pNO${}_{\mathrm{3}}^{-}$ ) in spring and winter. Compared with O₃ photolysis, HONO photolysis has long been an important source of OH except for summer afternoons. Observation of HONO across four seasons with various auxiliary parameters improves the comprehension of HONO chemistry in southeastern coastal China.