From Molecular Topography to Ozone Pollution: Species Sources and Photochemical Kinetics of Individual Organic Peroxyl Radicals

Abstract Ground-level ozone (O3) poses significant threats to global public health and climate change. Organic peroxyl radicals (RO2) serve as crucial intermediates in atmospheric O3 formation. Although individual RO2 species exhibit distinct reactivities, the quantification and source attribution of individual RO2 species remain poorly understood. Here, we address the challenge by integrating high-resolution field observations with fundamental theoretical kinetics within a novel hybrid receptor-kinetic modeling framework. The concentration and composition of RO2 species exhibit significant seasonal and diurnal dependencies. In summer, the 19 RO2 pool was characterized by a substantial contribution from biogenic sources (29%), particularly isoprene-derived species (ISOPOBO2). Conversely, the wintertime RO2 composition shifts, dramatically dominated by industrial emissions (41%), notably ethylene-derived species (HOCH2CH2O2). Source apportionment via the RO2+NO pathway further demonstrates that O3 photochemical formation potentials align closely with the kinetics of RO2 production. A data-driven machine learning model effectively captures the contribution of individual RO2 species to O3 formation in summer, but it shows significant deviations from kinetic simulations in winter. The framework establishes a dynamic framework to support daytime O3 mitigation by quantifying the high-time-resolution RO2 radical pool from field VOCs measurements.