Afforestation and Emission Cuts: Dual Drivers for China's Clean Air and Carbon Neutrality.

Under China's carbon neutrality and "Beautiful China" agendas, air pollution control has entered a new phase of synergistic carbon and pollutant mitigation. Meanwhile, large-scale afforestation is projected to strengthen natural carbon sinks but may also elevate emissions of biogenic volatile organic compounds (BVOCs) that enhance ozone (O3) and secondary organic aerosol (SOA) formation. However, their interaction with deep anthropogenic emission reductions and the resulting air quality outcomes remains an unresolved puzzle. Here, we assess the interactive effects of large-scale afforestation and anthropogenic emission reductions on O3 and PM2.5 concentrations in China using high-resolution emission inventories integrated with an advanced chemical transport model. Our results show that afforestation at its maximum potential could raise summer BVOC emissions in China by 3.20-3.82 Tg (20%-24% of current level), mainly across southern China. Under current anthropogenic emissions, these BVOC emissions elevate summer averaged MDA8 O3 and PM2.5 concentrations in eastern China by 0.74 ppbv (-0.09 to 5.93 ppbv) and 0.39 μg/m3 (0.02 to 3.47 μg/m3), accounting for 15% and 30% of the total BVOC-induced increases, respectively. In contrast, with continued anthropogenic emission reductions under carbon neutrality, the O3 response to afforestation shifts from enhancement to slight suppression, while SOA-related PM2.5 formation declines by 67%. Moreover, for identical afforestation extents, differences in tree species composition alone can reduce local O3 impacts to less than one-third. These findings reveal coordinated strategies aligning afforestation planning with emission-reduction pathways can more effectively improve air quality while advancing carbon neutrality goals, thereby safeguarding public health.