Biogenic volatile organic compounds dominated the near-surface ozone generation in Sichuan Basin, China, during fall and wintertime

The complex air pollution driven by both Ozone (O-3) and fine particulate matter (PM2.5) significantly influences the air quality in the Sichuan Basin (SCB). Understanding the O-3 formation during autumn and winter is necessary to understand the atmospheric oxidative capacity. Therefore, continuous in-site field observations were carried out during the late summer, early autumn and winter of 2020 in a rural area of Chongqing. The total volatile organic compounds (VOCs) concentration reported by a Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) were 13.66 +/- 9.75 ppb, 5.50 +/- 2.64 ppb, and 9.41 +/- 5.11 ppb in late summer, early autumn and winter, respectively. The anthropogenic VOCs (AVOCs) and biogenic VOCs (BVOCs) were 8.48 +/- 7.92 ppb and 5.18 +/- 2.99 ppb in late summer, 3.31 +/- 1.89 ppb and 2.19 +/- 0.93 ppb in autumn, and 6.22 +/- 3.99 ppb and 3.20 +/- 1.27 ppb in winter. A zero-dimensional atmospheric box model was employed to investigate the sensitivity of O-3-precursors by relative incremental reactivity (RIR). The RIR values of AVOCs, BVOCs, carbon monoxide (CO), and nitrogen oxides (NOx) were 0.31, 0.71, 0.09, and -0.36 for late summer, 0.24, 0.59, 0.22, and -0.38 for early autumn, and 0.30, 0.64, 0.33 and -0.70 for winter, and the results showed that the O-3 formation of sampling area was in the VOC-limited region, and O-3 was most sensitive to BVOCs (with highest RIR values, > 0.6). This study can be helpful in understanding O-3 formation and interpreting the secondary formation of aerosols in the winter.