Greening Pattern in China Would Be More Likely to Affect Summer Surface Ozone Over the Megacity Clusters

Satellite data reveal that China has significantly increased its vegetation cover since 2000, and vegetation will maintain the increasing trend in the foreseeable future for becoming carbon neutral. However, limited work has examined the environmental impacts of vegetation greening because natural sources (i.e., biogenic volatile organic compounds, VOCs) have always been deemed to contribute less compared to anthropogenic sources. This study attempts to make a direct connection between ozone concentrations and leaf area of vegetation by presenting a regional modeling sensitivity analysis. We find that increasing vegetation greening is more likely to affect surface ozone over the megacity clusters where ozone chemistry is mainly dominated by VOCs-sensitive or transition regimes. Especially in the Beijing-Tianjin-Hebei (BTH) region, ozone concentrations respond strongly to the changes in leaf area of vegetation with an increase of up to 4.1 ppbv (4.7%) from 2000 to 2016. Furthermore, anthropogenic VOCs emission reductions are added into the future vegetation greening scenarios through 2030-2050 to assess how much anthropogenic VOCs reductions could counteract the effects of vegetation greening. For this, we consider three anthropogenic VOCs emission reduction strategies and two future assumed vegetation greening scenarios for sensitive simulations. Overall, we estimate that in 2030 a 10% anthropogenic VOCs reduction can counteract the impacts of vegetation greening for the focus megacity clusters in East China, and in 2050 a roughly 15% anthropogenic VOCs reduction can achieve the offset. Noticeably, China is sparing no effort to increase the vegetation cover, but the worry is that natural emissions over megacity clusters with highly dense vegetation could cause more surface ozone pollution, which may increase the pressure of anthropogenic VOCs reductions. This study emphasizes the need to consider the underappreciated effects of vegetation greening for future policies aimed at mitigating ozone pollution in China