Measurement report: 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 this work, the VOC species in Xinxiang, a mid-sized city located in Henan Province in central China, were measured and analysed from November 5th to December 3rd, 2018. Based on online monitoring with proton transfer reaction-mass spectrometry (PTR-MS) and canister grab samples, 53 VOC species are obviously detected, and the most abundant categories are oxygenated VOCs (OVOCs) and benzenoids. Compared with field measurements in other regions, the mixing ratios of BTEX (benzene, toluene, ethylbenzene, and xylene), acetaldehyde, and C3 carbonyls are at high levels, indicating intensive anthropogenic emissions in Xinxiang. According to the positive matrix factorization (PMF) model, benzenoids are mainly emitted from solvent evaporation (~47 %), residential heating (~19 %), industrial emission (~16 %), and vehicle exhaust (~10 %), while the contributions from biogenic and secondary sources as well as thermal power generation are minor. However, the emissions of total OVOCs from the six resolved sources are similar. The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) results show that the transport contribution for VOCs is not intensive, but the cities within Henan Province or in the neighbouring provinces may influence the mixing ratios to some extent. The roles of benzenoids and OVOCs in SOA formation are investigated by estimating the mass of oxidation products and rates of OH radical production. Among the observed VOCs, toluene has the largest SOA formation potential (SOAFP), while its weight in SOA formation declines with the aggravation of pollution. On the other hand, the SOA concentration shows a good relationship with OH exposure, which highlights the importance of the atmospheric oxidation capacity, especially in polluted periods. Formaldehyde is the strongest radical contributor, and the contribution of acetaldehyde is also significant in this study. Furthermore, solvent evaporation, industrial emissions, and vehicle exhaust are estimated as the top three anthropogenic contributors with the highest SOAFP and radical contribution rate.