Abstract
Abstract. Despite local emission reductions, severe haze events remain a serious issue in Beijing. Previous studies have suggested that both greenhouse gas increases and aerosol decreases are likely to increase the frequency of weather patterns conducive to haze events. However, the combined effect of atmospheric circulation changes and aerosol and precursor emission changes on Beijing haze remains unclear. We use the Shared Socioeconomic Pathways (SSPs) to explore the effects of aerosol and greenhouse gas emission changes on both haze weather and Beijing haze itself. We confirm that the occurrence of haze weather patterns is likely to increase in future under all SSPs and show that even though aerosol reductions play a small role, greenhouse gas increases are the main driver, especially during the second half of the 21st century. However, the severity of the haze events decreases on decadal timescales by as much as 70 % by 2100. The main influence on the haze itself is the reductions in local aerosol emissions, which outweigh the effects of changes in atmospheric circulation patterns. This demonstrates that aerosol reductions are beneficial, despite their influence on the circulation.
Highlights
Over a million premature deaths in China were attributed to poor air quality in 2010, accounting for over 30 % of the mortality due to air pollution worldwide (Lelieveld et al, 2015; Zhang et al, 2017)
This study investigated 21st century changes in Beijing haze events using CMIP6 models
The opposing impacts of aerosols on the circulation patterns can be seen in the near future (2025–2034) in Shared Socioeconomic Pathways (SSPs) 3–7.0, where aerosol emissions continue to increase, moderating increases in the haze indices
Summary
Over a million premature deaths in China were attributed to poor air quality in 2010, accounting for over 30 % of the mortality due to air pollution worldwide (Lelieveld et al, 2015; Zhang et al, 2017). New future scenarios used in the Sixth Coupled Model Intercomparison Project (CMIP6), the Shared Socioeconomic Pathways (SSPs), are designed to cover a wide range of narratives of socioeconomic development and energy consumption in the 21st century and capture a much wider range of uncertainty in aerosol emission pathways (Fig. 1) than the Representative Concentration Pathways used in CMIP5 (Riahi et al, 2017) This presents an opportunity to explore the relative roles of aerosol and greenhouse gases in driving changes in the HWI and the interplay between the effects of aerosol changes on the atmospheric circulation and on the composition of the haze itself. We quantify the relative importance of forced changes in the atmospheric circulation and the direct effect of emission reductions on Beijing haze
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