Enhanced understanding of atmospheric blocking modulation on ozone dynamics within a high-resolution Earth system model

Abstract. High surface ozone concentrations pose substantial health risks, yet understanding the factors influencing ozone levels, especially the role of large-scale circulations, remains incomplete. A key challenge is accurately modeling both large-scale circulations and ozone concentrations. Using a high-resolution Earth system model (25 km atmospheric resolution), we explore how local meteorology and large-scale circulations affect ozone levels. Our results show that heat waves can trigger substantial increases in ozone concentrations by stimulating biogenic volatile organic compound (BVOC) emissions during the summers of 2015–2019. For example, maximum daily 8 h (MDA8) ozone concentrations during heat waves increase by 12.0 ppbv in the southeastern US, 9.7 ppbv in Europe, 17.6 ppbv in North China, and 9.0 ppbv in central eastern China compared to non-heat-wave periods. In addition to local effects, atmospheric blocking strongly influences downstream meteorological conditions and ozone formation. Focusing on ozone pollution in eastern China, we identify three major pathways of Rossby wave propagation based on blocking locations: the Euro-Atlantic sector, northern Russia, and the North Pacific. These pathways lead to increased air temperature and intensify downward surface solar radiation downstream. The impact of blocking is most pronounced in central eastern China, where MDA8 ozone concentrations increase by 5.9 to 10.7 ppbv during blocking compared to non-blocking periods, followed by North China (2.1 to 4.9 ppbv). Blocking also stimulates BVOC emissions, enhancing MDA8 ozone concentrations by 10.6 to 15.9 ppbv in these regions. These findings highlight the critical role of large-scale atmospheric circulation in shaping regional air quality, especially under a warming climate.