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Ground surface ozone (O3) is an emerging concern in China due to its complex formation process. In August 2020, field measurements of O3, NOx, and volatile organic compounds (VOCs) were carried out in Hefei's western suburbs. The pollution features of VOCs and O3 formation were thoroughly analyzed. The total VOC concentration was 42.26 ppb, with the dominant contributor being oxygenated VOCs (OVOCs). Seven emission sources were recognized using the positive matrix factorization (PMF) model, including aged air masses, combustion sources, fuel evaporation, industrial emissions, vehicular emission, solvent utilization, and biogenic emission. Ozone generation mainly occurred under an NOx-limited regime based on the zero-dimensional box model analysis. According to the scenario analysis, the 13% cut in O3 might be achieved by the 10% and 30% reduction in NOx and VOCs, respectively. The O3 budget analysis demonstrates its high ozone production rate during the pollution period. The influence of regional transport cannot be ignored for high O3 pollution. This paper provides scientific evidence for O3 production and the strategies of reducing O3 by controlling its precursors. [ABSTRACT FROM AUTHOR]

Organic peroxy radicals (RO2) as key intermediates in tropospheric chemistry exert a controlling influence on the cycling of atmospheric reactive radicals and the production of secondary pollutants, such as ozone and secondary organic aerosols (SOA). Herein, we present a comprehensive study of the self-reaction of ethyl peroxy radicals (C2H5O2) by using advanced vacuum ultraviolet (VUV) photoionization mass spectrometry in combination with theoretical calculations. A VUV discharge lamp in Hefei and synchrotron radiation at the Swiss Light Source (SLS) are employed as the photoionization light sources, combined with a microwave discharge fast flow reactor in Hefei and a laser photolysis reactor at the SLS. The dimeric product, C2H5OOC2H5, as well as other products, CH3CHO, C2H5OH and C2H5O, formed from the self-reaction of C2H5O2 are clearly observed in the photoionization mass spectra. Two kinds of kinetic experiments have been performed in Hefei by either changing the reaction time or the initial concentration of C2H5O2 radicals to confirm the origins of the products and to validate the reaction mechanisms. Based on the fitting of the kinetic data with the theoretically calculated results and the peak area ratios in the photoionization mass spectra, a branching ratio of 10 ± 5% for the pathway leading to the dimeric product C2H5OOC2H5 is measured. In addition, the adiabatic ionization energy (AIE) of C2H5OOC2H5 is determined at 8.75 ± 0.05 eV in the photoionization spectrum with the aid of Franck-Condon calculations and its structure is revealed here for the first time. The potential energy surface of the C2H5O2 self-reaction has also been theoretically calculated with a high-level of theory to understand the reaction processes in detail. This study provides a new insight into the direct measurement of the elusive dimeric product ROOR and demonstrates its non-negligible branching ratio in the self-reaction of small RO2 radicals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Self-reaction of C 2 H 5 O 2 and its cross-reaction with HO 2 studied with VUV photoionization mass spectrometry and high-level theoretical computations. • Key products CH 3 CHO, C 2 H 5 OH, C 2 H 5 O and C 2 H 5 OOH are directly observed in photoionization mass spectra and confirmed with photoionization spectra. • The elusive radical product C 2 H 5 O from the self-reaction is detected for the first time. • The ionization energies of C 2 H 5 O and C 2 H 5 OOH are determined. We present a study of the self-reaction of C 2 H 5 O 2 and its cross-reaction with HO 2 with VUV photoionization mass spectrometry. Hefei synchrotron radiation and a krypton discharge lamp are combined to ionize species. Key products including CH 3 CHO, C 2 H 5 OH, C 2 H 5 O and C 2 H 5 OOH formed from the reactions are directly observed and confirmed. In particular, the radical product C 2 H 5 O from the self-reaction is detected for the first time. The ionization energies of C 2 H 5 O and C 2 H 5 OOH are determined and the Franck-Condon factors are calculated to fit the photoionization spectra. Moreover, kinetic experiments are performed to confirm the products' assignment and provide detailed reaction mechanism. [ABSTRACT FROM AUTHOR]