Recently, a new study in Nature Communications explored the ecological impacts of fire air pollution. Increases in O3 and aerosols have opposite impacts on plant health. O3 is phytotoxic and reduces plant photosynthesis, while aerosols may promote photosynthesis by enhancing diffuse radiation. It is unclear what’s the net impacts of these pollutants on biosphere from the same fire. This study combined three state-of-the-art models and a full set of observations from ground sites, satellites, and literature, to quantify the net impacts of fire O3 and aerosols on gross primary productivity (GPP), a metric representing total photosynthesis of forests.
Results show that surface O3 reduces global GPP by 4.9 Pg C (3.6%) every year, in which fire O3 accounts for ~20%. In contrast, global aerosols enhance annual GPP by 1.0 Pg C (0.8%) with fire contributions of only 5%. The fertilization effect of fire aerosols is very limited, likely because fire emissions usually occur in tropical forests where dense cloud masks the aerosol effects. Consequently, the net impact of fire air pollution is dominated by O3, leaving a reduction of 0.9 Pg C (0.6%) in annual GPP.
Regionally, fire air pollution causes larger damages to forest productivity. For example, the 2006 large fire in Indonesia reduces local GPP by 3.6%. Furthermore, the fire pollution can cause impacts through long-range transport. We find GPP reductions of 0.6% in eastern U.S. and 0.5% in eastern China where fire events are very limited. In those regions, high level of background O3 from human activities provides such a sensitive environment that even a mild increase in O3 by fires can cause a discernable influence.