A high spatiotemporal resolution anthropogenic VOC emission inventory for Qingdao City in 2016 and its ozone formation potential analysis

Abstract

Accurate and gridded emission inventories are crucial for better air quality modeling and air pollution policy making. As the economic center of the Shandong province and part of the first batch of open coastal cities in China, Qingdao has been frequently plagued by volatile organic compound (VOC) pollution along with its rapid economic development and urbanization in recent years. In this study, a high spatiotemporal resolution VOC emission inventory for Qingdao was established for the year 2016 using updated source-specific emission factors and the latest activity data for different sources. The anthropogenic sources considered in this study are classified into seven major sources and 46 subcategories. The results indicated that a total of 151.5 kt of VOCs were emitted in Qingdao in 2016. The three largest emission sources, industrial process, on-road mobile, and solvent use sources accounted for 49.9% 20.1%, and 14.1% of the total VOC emissions, respectively. Spatially, the Huangdao District (57.9 kt), the Chengyang District (15.4 kt), and Pingdu City (15.1 kt) were the top three emitters of VOCs. The high concentration of VOCs was mainly distributed in the central areas of Qingdao city and the emissions distribution was highly consistent with its road network. The maximum monthly VOC emissions occurred in June (14.4 kt) and the minimum monthly VOC emissions occurred mainly in February (9.5 kt). The uncertainties in the emission inventory were quantified using a Monte Carlo simulation provided by the Oracle Crystal Ball software. There exist relatively high uncertainties in the on-road mobile (-84.79%, 252.07%), biomass burning (-65.38%, 134.77%) and industrial process (-36.08%, 133.62%) sources. For the complicated species and different reaction rates of ozone formation, the control of the amount of VOCs emitted and the highly reactive VOCs are equally important. Based on the emissions of individual VOC species and the corresponding maximum incremental reactivity (MIR), the ozone formation potential (OFP) profiles of Qingdao City were constructed. The results indicated that alkenes/alkynes and aromatics contributed the most to the OFP and that m/p-xylene, ethylene, propylene, formaldehyde, toluene, trans-2-butene, cis-2-butene, 1-butene, o-xylene, and 1-pentene were the top 10 individual VOC species contributing to the OFP. The contribution of industrial process and on-road mobile sources accounted for 37.5% and 24.5% of the total OFP in Qingdao City, respectively. Both the large VOC emission and OFP indicate that the focus of VOC emission control should be on industrial process and on-road mobile sources in Qingdao City.