Characteristics and sources of non-methane VOCs and their roles in SOA formation during autumn in a central Chinese city

Abstract

Volatile organic compounds (VOCs) are essential in secondary organic aerosol (SOA) formation due to their dual roles as precursors and oxidant producers. In order to explore the dominant contributions of SOA formation from VOCs in central China, 53 VOC species were observed with proton transfer reaction-mass spectrometry (PTR-MS) and canister grab samples in Xinxiang, a mid-sized city located in Henan Province, from November 5th to December 3rd, 2018. The result showed that anthropogenic emissions were intensive compared with many studies in the world. Among the observed VOCs, benzene and toluene had the largest SOA formation potential (SOAFP), and their contributions in SOA formation kept stable with the aggravation of pollution. Among VOCs, formaldehyde was the strongest radical contributor, and the contribution of acetaldehyde was also found significant in this study, especially in polluted periods. Based on the positive matrix factorization (PMF) model, benzenoids (mainly single-ring aromatics) were majorly emitted from chemical process, solvent evaporation, and residential heating, with a total fraction of 75%, and these sources were estimated to have largest SOAFP. However, thermal power generation, chemical process, and solvent evaporation had highest radical contribution rates. According to the backward trajectory analysis, the VOC concentrations were dominated by local emissions. Emissions in the surrounding provinces occupied fractions of 33%–42% in the five sources. Therefore, regional collaborative emission reduction is also important.