The effect of different Climate and Air Quality policies in China on in situ Ozone production in Beijing

Abstract. In recent years, clean air policies have led to reductions in air pollution across China. Alongside this, emerging carbon neutrality (CN) policies that aim to address the impacts of climate change may also deliver air quality (AQ) co-benefits or climate penalties. Different CN policies will lead to different changes in volatile organic compound (VOC), NO_x, and particulate matter (PM) emissions, which will in-turn impact the photochemical production of secondary pollutants such as ozone (O₃). It is currently unclear how different combinations of AQ and CN policies may impact in situ O₃ production across China in the future. A detailed chemical box model incorporating the Master Chemical Mechanism was developed to investigate the impact of combined AQ and CN policies on O₃ formation in Beijing. The Multi-resolution Emission Inventory model for Climate and air pollution research (MEIC) and the Dynamic Projection model for Emissions in China (DPEC) were used to estimate future pollutant mixing ratios, relative to ambient observations of 35 VOCs, NO_x, CO and aerosol surface area (ASA) during the APHH-Beijing 2017 summer campaign. The most ambitious policy scenario, “Ambitious Pollution 1.5D goals", led to the largest reduction in O₃ production by 2060, but was not the most impactful scenario for reducing O₃ production between 2030–2045. Larger reductions were observed under the “Ambitious Pollution Neutral goals” policy which focuses on achieving net zero by 2060. O₃ production was found to be most sensitive to changes in the OLE2 group of VOCs (alkenes where k_OH > 7 x 10⁴ ppm^-1 min^-1;  a 5 % increase in OLE2 increased simulated O₃ production by 1.12 %). However, reducing less reactive but higher concentration species in Beijing (including methanol and short-chain alkanes) led to larger reductions in O₃ production under all scenarios. O₃ production was not sensitive to changes in ASA, with a 69 % decrease in ASA leading to a change of < 1 % in O₃. However, doubling biogenic VOCs in the model further increased O₃ production in 2060 under all future scenarios by up to 18 %, indicating that the influence of future climate-induced changes in biogenic emissions may have a significant impact on in situ O₃ formation in Beijing. This study highlights that the emission trajectories of certain specific VOCs are highly influential in determining possible future O₃ air quality effects that may arise from increasing ambient temperatures and decarbonisation in Beijing.