Significant Contributions of Gasoline Evaporation to Wintertime VOCs: Evidence from Online Measurements

The evaporation of gasoline serves as an important contributor to volatile organic compounds (VOCs) within urban regions. However, most previous studies have focused on summertime gasoline evaporation, with relatively limited attention to wintertime emissions. Within the present research, online VOC monitoring was carried out at three urban locations across Beijing over the winter seasons of 2014–2015 and 2021–2022. A wintertime gasoline evaporation VOC source profile was established using enhancement ratio analysis and positive matrix factorization, based on observations at a site near a gasoline station. The results show that n-butane dominated wintertime gasoline evaporation VOCs (35%), exceeding i-pentane (20%), in contrast to the i-pentane dominance reported in previous studies. The chemical mass balance (CMB) model was then applied to apportion VOC sources and assess the sensitivity to different gasoline evaporation source profiles. Gasoline evaporation was found to contribute 12–17% of wintertime VOCs, 2.3–3 times higher than estimates based on the literature profiles. Comparisons between the winters of 2014–2015 and 2021–2022 reveal a 63% decrease in VOC concentrations, with the coal combustion contribution dropping by 85% and vehicular exhaust and gasoline evaporation by 51–60%. These findings demonstrate that gasoline evaporation remains a non-negligible VOC source in winter and highlight that season- and observation-based source profiles are essential for reliable VOC source apportionment and effective air quality management.