Characteristics and sources of ambient Volatile Organic Compounds (VOCs) at a regional background site, YRD region, China: Significant influence of solvent evaporation during hot months.

Continuous measurement of 98 volatile organic compounds (VOCs) was conducted during 2017-2019 at a regional background site (Shanxi) located at northeast of Zhejiang Province, YRD region, China. The average concentration of total VOCs (TVOCs) was 25.4 ± 18.4 ppbv, and an increasing trend (+12.2 %) was observed. Alkanes were the most abundant VOC group among all seasons, accounting for 43.5 % of TVOCs. Oxygenated VOCs (OVOCs), aromatics, halides and alkenes contributed 15.9 %, 15.7 %, 11.7 % and 10.3 % of TVOCs concentration, respectively. Biogenic VOCs (BVOCs) and OVOCs showed distinguished diurnal cycle from primary anthropogenic VOCs. Photochemical reactivity analysis based on ozone formation potential (OFP) and OH loss rate (LOH) indicated that aromatics and alkenes were the most significant contributor, respectively. Toluene, xylene (m/p- and o-), ethene and propene were the largest contributor of annual OFP, with the mean OFP being 33.8 ± 44.3 µg·m-3, 31.9 ± 32.1 µg·m-3, 9.29 ± 11.4 µg·m-3, 22.1 ± 21.3 µg·m-3 and 12.8 ± 19.5 µg·m-3, respectively. Seven sources were identified with positive matrix factorization (PMF): petrochemical industry (13.8 %), biogenic emission (1.0 %), solvent usage-toluene (16.9 %), vehicular exhaust (43.8 %), Integrated circuits industry (3.8 %), solvent usage-C8 aromatics (10.9 %), and gasoline evaporation (9.8 %). Vehicular exhaust was the most significant source (43.8 %) during the whole measurement period. Solvent usage, petrochemical industry, and gasoline evaporation showed high temperature dependency. The integrated contribution of solvent usage and industrial processes were higher than vehicular exhaust during hot months. These sources also have higher chemical reactivities and can contribute more on O3 formation. Our results are helpful on determining the control strategies aiming at alleviating O3 pollution.

Chemical characterization, formation mechanisms and source apportionment of PM2.5 in north Zhejiang Province: The importance of secondary formation and vehicle emission.

PM2.5 affects air quality, therefore, chemical evolution, formation mechanism and source identification of PM2.5 are essential to help figure out mitigation measures. PM2.5 and its constituents were comprehensively characterized with highly time-resolved measurements from 2019 to 2020 in north Zhejiang Province (Shanxi, SX) for the first time, with an emphasis on the contribution of secondary formation and vehicle emission to PM2.5. Secondary inorganic ions (sulfate: 3.86 µg/m3, nitrate: 7.82 µg/m3 and ammonium: 4.59 µg/m3, SNA) were found to be the major components (54%) in PM2.5 (29.70 µg/m3). The highly consistence of nitrate, sulfate and secondary organic compounds (SOC) with Ox (NO2 + O3) or RH indicated the importance of photochemical oxidation and heterogeneous reaction in different scenarios. Higher atmospheric oxidative potential facilitated the SOC formation in spring. The PM2.5 mass was apportioned to eight sources resolved by positive matrix factorization (PMF): secondary nitrate (9.63 µg/m3), secondary sulfate (5.14 µg/m3), vehicle emission (7.26 µg/m3), coal combustion (2.39 µg/m3), biomass burning (1.38 µg/m3), soil dust (0.86 µg/m3), industry emission (0.50 µg/m3), and ship emission (0.32 µg/m3). Secondary nitrate (35%) and sulfate (19%) formation and vehicle emission (26%) were the main factors contributing to the PM2.5. Furthermore, the contribution of secondary nitrate formation increased with elevating PM2.5 concentration. Regional transport was synthetically studied by chemical and backward trajectory analysis, reflecting that secondary nitrate contributed severely to the air quality at SX, while vehicle emission contribution enhanced when atmosphere was stagnant. This study first provides long-term comprehensive chemical characterization and source apportionments of PM2.5 pollution in north Zhejiang, which may provide some guidance for the air pollution control.