Source apportionment of VOCs and ozone formation potential and transport in Chengdu, China

The meteorological conditions and monitoring data of ozone and its precursors (NOx, VOCs) in Chengdu during summer (June–August 2019) were analyzed. The average concentration of VOCs in Chengdu during the summer is 36.63 ± 12.92 ppbv. The daily time series variation of ozone concentration presented unimodal type distribution, reaching the peak in the afternoon (4:00–6:00 p.m.). The heavy ozone pollution was basically accompanied by meteorological conditions of high temperature, low humidity, and low wind speed. The source apportionment of VOCs was conducted by using the positive matrix factorization (PMF) receptor model. The industrial sources, vehicle emission and fuel evaporation were identified as the main sources of VOCs, contributing 26.43%, 21.97% and 17.63% to VOCs respectively. The ozone formation potential (OFP) values indicated that the key active species were aromatics and alkenes represented by m/p-xylene and ethylene. The ridge line of the EKMA curve showed that the VOCs/NOx ratio was about 9.5, hence the emission reduction ratio of VOCs should be much higher than that of NOx in the summer aiming for ozone prevention and control work. The results of backward trajectory clustering, potential source contribution function (PSCF), and concentration-weighted trajectory (CWT) showed that ozone in Chengdu was affected by both local and regional sources in the summer. The potential source regions of ozone are mainly come from local urban areas and eastern and southern Sichuan cities.