The relationship between the intensified heat waves and deteriorated summertime ozone pollution in the Beijing-Tianjin-Hebei region, China, during 2013-2017

Summertime ozone (O-3) pollution has frequently occurred in the Beijing<bold>-</bold>Tianjin<bold>-</bold>Hebei (BTH) region, China, since 2013, resulting in detrimental impacts on human health and ecosystems. The contribution of weather shifts to O-3 concentration variability owing to climate change remains elusive. By combining regional air chemistry model simulations with near-surface observations, we found that anthropogenic emission changes contributed to approximately 23% of the increase in maximum daily 8-h average O-3 concentrations in the BTH region in June<bold>-</bold>July<bold>-</bold>August (JJA) 2017 (compared with that in 2013). With respect to the weather shift influence, the frequencies, durations, and magnitudes of O-3 exceedance were consistent with those of the heat wave events in the BTH region during JJA in 2013<bold>-</bold>2017. Intensified heat waves are a significant driver for worsening O-3 pollution. In particular, the prolonged duration of heat waves creates consecutive adverse weather conditions that cause O-3 accumulation and severe O-3 pollution. Our results suggest that the variability in extreme summer heat is closely related to the occurrence of high O-3 concentrations, which is a significant driver of deteriorating O-3 pollution.