Measurement report: Volatile organic compound characteristics of the different land-use types in Shanghai: spatiotemporal variation, source apportionment and impact on secondary formations of ozone and aerosol

Abstract

Abstract. Volatile organic compounds (VOCs) have important impacts on air quality, atmospheric chemistry and human health. In order to identify the spatiotemporal variations, sources and ozone (O3) and secondary organic aerosol (SOA) formation potentials of the atmospheric VOCs, a concurrent multi-site observation campaign was performed at the supersites of Shanghai, East China, in the first three months of 2019. The sampling sites are located at the different land-use types, including an industrial district (the Jinshan site: JS), residential and commercial mixed districts (the Pudong site: PD) and a background district (the Qingpu site: QP) of Shanghai. During the observation period, the average VOC concentrations were sensitive to the land-use types in the order of the JS (21.88 ± 12.58 ppb) > PD (21.36 ± 8.58 ppb) > QP (11.93 ± 6.33 ppb) sites. The predominant VOC category was alkanes (49.32 %–71.48 %), followed by aromatics (10.70 %–21.00 %), alkenes (10.13 %–15.30 %) and alkynes (7.69 %–14.80 %) at the studied sites. There were distinct diurnal variations and “weekend effects” of VOCs at the sampling sites. The VOC concentrations increased by 27.15 %, 32.85 % and 22.42 % during the haze events relative to the clean days. Vehicle exhaust was determined as the predominant VOC source. The second-largest VOC contributor was identified as industrial production at the JS and PD sites, while it proved to be fuel production and evaporation at the QP site. The industrial emission and biomass burning showed slight contributions to VOC concentrations at the QP and JS/PD sites, respectively. This was consistent with the regional characteristics of anthropogenic activities dominated by land-use types. High potential source contribution function (PSCF) values primarily appeared in the northeastern and northern areas surrounding sampling sites, suggesting strong local emissions. The ozone formation potential (OFP) values of each land-use type were in the order of the JS (50.89 ± 2.63 ppb) > PD (33.94 ± 1.52 ppb) > QP (24.26 ± 1.43 ppb) sites, with alkenes and aromatics being the predominant contributors. Secondary organic aerosol formation potential (SOAFP), mainly contributed by the aromatics, was highest at the JS site (1.00 ± 2.03 µg m−3), followed by the PD (0.46 ± 0.88 µg m−3) and QP (0.41 ± 0.58 µg m−3) sites. The VOC–PM2.5 sensitivity analysis showed that VOCs at the QP site displayed a more rapid increment along with the increase in PM2.5 values relative to the other two sites. Alkenes and aromatics are both the key concerns in controlling the VOC-related pollution of O3 and SOA in Shanghai. These findings provide more information on accurate air-quality control at a city level in China. The results shown herein highlight that the simultaneous multi-site measurements with the different land-use types in a megacity or city cluster could be more appropriate for fully understanding the VOC characteristics relative to a single-site measurement performed normally.