Unexpected Fast Photochemistry Emerges in Cool Seasons China

Ozone is a crucial air pollutant that damages human health and vegetation. As it is formed by the sunlit oxidation of the nitrogen oxides and volatile organic compounds, the current ozone mitigation strategies are primarily focused on summer. By analysing ozone pollution episodes in eastern China, observed daily total oxidants accumulation in cool seasons (spring and autumn: 60 ppb and winter 40 ppb) is comparable to that measured in summer (60 ppb) indicating fast photochemical production of secondary pollutants including ozone over the year. Unrecognized fast radical primary productions is found to counteract the increased termination of hydroxyl radical and dis-benefit meteorological conditions to maintain the rapid total oxidant formations in cool seasons. Elucidating and regulate the primary radical sources may be critical for the secondary air pollution control in cool seasons.