Ambient volatile organic compounds at Wudang Mountain in Central China: Characteristics, sources and implications to ozone formation

A continuous measurement of ambient volatile organic compounds (VOCs) was carried out from May to June 2018 at a background site, the Wudang Mountain (Mt. Wudang) in Central China. The characteristics, sources of VOCs and their contributions to ozone formation were investigated for the first time in this area. Based on the National Ambient Air Quality Standard, 29 O-3 non-attainment days were identified. The average mixing ratio of 82 total VOCs (Sigma VOCs) was 12.17 +/- 3.66 ppb. Higher mixing ratios of individual species were found compared with those measured at global baseline sites. The results revealed that the dominant VOCs components were alkanes and OVOCs, accounting for 79.92%. Five sources, i.e. industrial processes, fuel evaporation, vehicular exhaust, solvent utilization and biogenic emission were identified by the positive matrix factorization (PMF) model. From potential source contribution function (PSCF) analysis, local area and the adjacent provinces especially Shaanxi province, had some extent influence on Mt. Wudang. The OH radical loss rate (L-OH) and ozone formation potential (OFP) calculations revealed that biogenic emission and vehicular exhaust were both the major sources for ozone formation. Through the Observation-Based Model (OBM) simulation, the daytime average net ozone production rate was 4.1 ppb/h and the ozone production pathway was dominated by the reaction of HO2 + NO. This study shows that local emission and long-range transport of air pollutants should be taken into account for developing the science-based air pollution control strategies at Mt. Wudang.