Atmospheric Hydrogen Peroxide During Autumn in Beijing: Source Analysis and Effect on Sulfate Formation

Abstract Atmospheric hydrogen peroxide (H 2 O 2 ) is a critical oxidant that influences atmospheric chemistry, playing a pivotal role in the cycling of hydroperoxyl (HO 2 ) and hydroxyl (OH) radicals, ozone (O 3 ) formation, and sulfate aerosol production. However, the current understanding of its concentration level, sources and atmospheric effects are still poor. This study investigates the drivers of elevated H 2 O 2 concentrations during autumn in Beijing using comprehensive field observations from October to November 2021. The averaged H 2 O 2 concentration in the urban boundary layer of Beijing is 0.26 ± 0.03 ppb, peaking at 16:00. By integrating Random Forest Regression and relative incremental reactivity analysis, we systematically examine the influence of meteorological factors, trace gases, and photochemical reactions on H 2 O 2 concentrations. The result showed the significant contributions of temperature (T) and photochemical processes to H 2 O 2 production, while identifying key inhibitors such as nitrogen monoxide (NO). Additionally, we explore the role of H 2 O 2 in sulfate formation during haze pollution episodes, finding that although H 2 O 2 ‐mediated oxidation contributes to sulfate production, it is not the dominant pathway during the campaign. These findings underscore the complex interplay between meteorological factors, trace gases, and multiphase reactions in regulating H 2 O 2 concentrations and cycling, providing valuable insights into the dynamics of atmospheric oxidation processes and offer guidance for mitigating air quality issues in urban boundary layer.