LAUSR

Abstract. We identified scattered coal burning as the largest contributor to ambient volatile organic compounds (VOCs), exceeding traffic-related emissions, during the heating season (the cold season when fossil fuel is burned for residential heating) in Beijing prior to the rigorous emission limitations enacted in 2017. However, scattered coal is underestimated in emission inventories generally because the activity data are incompletely recorded in official energy statistics. Results of positive matrix factorization (PMF) models confirmed that coal burning was the largest contributor to VOC mixing ratios prior to the emission limitations of 2017, and a reduction in scattered coal combustion, especially in the rural residential sector, was the primary factor in the observed decrease in ambient VOCs and secondary organic aerosol (SOA) formation potential in urban Beijing after 2017. Scattered coal burning was included in a corrected emission inventory, and we obtained comparable results between this corrected inventory and PMF analysis particularly for the non-control period. However, a refined source subclassification showed that passenger car exhaust, petrochemical manufacturing, gas stations, traffic evaporation, traffic equipment manufacturing, painting, and electronics manufacturing are also contributors to ambient VOCs. These sources should focus on future emission reduction strategies and targets in Beijing. Moreover, in other regions with scattered coal-based heating, scattered coal burning is still the key factor to improve the air quality in winter.