Accurate Elucidation of Oxidation Under Heavy Ozone Pollution: A Full Suite of Radical Measurement In the Chemical-complex Atmosphere

A full suite of radical measurements (OH, HO₂, RO₂, and k_OH) was established in Yangze River Delta (YRD) region to accurately elucidate the limitations of oxidation processes in the chemical-complex atmosphere. The diurnal peaks of radicals exhibited considerable variations in 3.6 to 27.1×10⁶ cm^-3 for OH, 2.1 to 33.2×10⁸ cm^-3 for HO₂, and 4.9 to 30.5×10⁸ cm^-3 for RO₂. The simulated results provided by the RACM2-LIM1 mechanism failed to adequately match the observed data both in radical concentration and experimental budget at a heavy ozone pollution episode. Sensitivity tests utilizing a comprehensive set of radical measurements revealed that the reactive aldehyde chemistry effectively complements the regeneration of OH radicals with 4.4% - 6.0% compared to the base scenario, while the concentrations of HO₂ and RO₂ radicals have shown increments of about 7.4% and 12.5%, respectively. The incorporation of larger alkoxy radicals stemming from monoterpenes has refined the consistency between measurements and modeling in the context of ozone production under elevated NO levels, diminishing the disparity from 4.17 to 2.33. Moving forward, by implementing a comprehensive radical detection approach, further investigations should concentrate on a broader range of OVOCs to rectify the imbalance associated with RO₂ radicals, thereby providing a more precise understanding of oxidation processes during severe ozone pollution episodes.