The dominant role of temperature in seasonal ozone sensitivity changes in China

Abstract

In recent years, surface ozone pollution in China has been extending from the warm to the cold seasons. The effectiveness of emission control for ozone pollution mitigation depends on the sensitivity of ozone to its precursors. Observations reveal a clear seasonal contrast in ozone precursor sensitivity across cities in China. However, the underlying drivers of different seasonal ozone precursor sensitivity remain unclear, posing a major challenge for developing effective seasonal control strategies. Here we use comprehensive measurements and model simulations to demonstrate that temperature changes have a critical role in shaping this seasonal variation in ozone sensitivity, which matters more than the changes in anthropogenic emissions and actinic flux. From winter to summer, the temperature effect is further intensified by concurrent changes in water vapour and actinic flux, enhancing radical primary production and shifting ozone sensitivity towards a nitrogen oxide-limited regime through a synergistic mechanism. The temperature-driven synergistic mechanism indicates a volatile organic compounds-limited regime during cold seasons, in which sustained nitrogen oxide emission reductions can substantially increase ozone. To avoid prolonging the ozone pollution season, emissions of volatile organic compounds would need to be reduced at approximately twice the rate currently implemented. These findings suggest that the temperature-driven synergistic effect must be fully accounted for when designing long-term ozone pollution mitigation strategies. Ozone regime analyses suggest that temperature outweighs anthropogenic emissions and actinic flux in controlling seasonal variations in ozone sensitivity over China.