Reply on RC1

Abstract

Volatile organic compounds (VOCs) have important impacts on air quality, climate, and human health. In order to identify the characteristics, sources and secondary formation potentials of the atmospheric VOCs varying with land use types, a concurrent multi-site observation campaign was performed at the supersites of Shanghai, East China, in the first three months of 2019. During the observation period, the average VOC concentrations were 21.39, 21.36 and 11.93 ppb at the Jinshan (JS), Pudong (PD) and Qingpu (QP) sites, respectively. The predominant VOC category was alkanes (49–61 %), followed by aromatics (11–21 %), alkenes (10–15 %) and alkyne (8–14 %) at the above sites. The sampling sites exhibited distinct diurnal variations and “weekend effects” of VOCs. The VOC concentrations increased by 27.15, 32.85 and 22.42 % during the haze events relative to the clean days during the measurements. 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 fuel evaporation was the second important source at the QP site. High potential source contribution function (PSCF) values appeared in the northeastern and northern Shanghai near the sampling sites, suggesting the strong local emissions. The secondary organic aerosol formation potential, mainly contributed by the aromatics, was higher at the JS site (1.00 μg m-3) than those at the PD (0.46 μg m-3) and QP (0.41 μg m-3) sites. The VOCs-PM2.5 sensitivity analysis showed that the VOCs at the QP site could be more sensitive to the PM2.5 concentration relative to the other two sites. The ozone formation potentials (OFP) were calculated to be 50.89, 33.94 and 24.26 ppb during the campaign at the JS, PD and QP sites, respectively. The VOCs-O3 sensitivity indicated that the VOCs-SO3 values varied at the different sites and were primarily controlled by the alkene-related reactions. Alkenes and aromatics are thus the key concerns in controlling the VOC-related pollution of SOA and O3 in the diverse districts of Shanghai. The findings of this study provide new insights into the accurate air-quality control at a city level in China due to a wide variety of land-use types. The results shown herein highlight that the simultaneous multiple-site measurements in the megacity or city cluster could be more appropriate to fully understand the VOC characteristics relative to a single-site measurement performed normally.