Characteristics and sources of volatile organic compounds (VOCs) in Shanghai during summer: Implications of regional transport

Intensive field measurements were carried out in urban Shanghai between 20th and 30th of May 2017, and the VOC characteristics and sources were investigated with a focus on the relative contributions of local emissions and regional transport, as well as on the potential source regions. The VOC characteristics and sources largely depended on the meteorological conditions, especially wind direction and wind speed. Generally, two kinds of episodes were associated with regional transport. In one scenario, pollutants were transported from areas upwind (north-to-northwest) of Shanghai, specifically the Suzhou-Wuxi-Changzhou and Nantong city clusters and were characterized by combustion emissions and aged air masses. In the other scenario, pollutants were transported from areas upwind (south-to-southeast) of Shanghai, specifically Ningbo-Zhoushan port, and were characterized by industrial emissions and aged air masses. Additionally, an episode associated with air masses from the clean area over the sea provided an opportunity to study the local emissions of VOCs in Shanghai. Vehicle exhaust and chemical industries, especially solvent usage, contributed a majority of the VOCs in urban Shanghai in summer, together accounting for more than 55%. The aromatic fraction of the PAMS in Shanghai was significantly higher than that in other regions in China. Regional transport and secondary formation were also important sources of VOCs, and their contribution ranged from similar to 15% to similar to 25% depending on the meteorological conditions, with an hourly maximum contribution as high as 67%. Fuel evaporation, especially leakage emissions, should be addressed in Shanghai. The present study highlights the fact that joint control of VOCs in conjunction with surrounding cities is critical for Shanghai.