Abstract
Fire emissions generate air pollutants ozone (O3) and aerosols that influence the land carbon cycle. Surface O3 damages vegetation photosynthesis through stomatal uptake, while aerosols influence photosynthesis by increasing diffuse radiation. Here we combine several state-of-the-art models and multiple measurement datasets to assess the net impacts of fire-induced O3 damage and the aerosol diffuse fertilization effect on gross primary productivity (GPP) for the 2002–2011 period. With all emissions except fires, O3 decreases global GPP by 4.0 ± 1.9 Pg C yr−1 while aerosols increase GPP by 1.0 ± 0.2 Pg C yr−1 with contrasting spatial impacts. Inclusion of fire pollution causes a further GPP reduction of 0.86 ± 0.74 Pg C yr−1 during 2002–2011, resulting from a reduction of 0.91 ± 0.44 Pg C yr−1 by O3 and an increase of 0.05 ± 0.30 Pg C yr−1 by aerosols. The net negative impact of fire pollution poses an increasing threat to ecosystem productivity in a warming future world.
Highlights
Fire emissions generate air pollutants ozone (O3) and aerosols that influence the land carbon cycle
The Yale Interactive terrestrial Biosphere (YIBs) model calculates O3 damages to gross primary productivity (GPP) as a function of stomatal O3 flux[25], which is dependent on both O3 concentrations ([O3]) and leaf stomatal conductance (Methods)
Compared with simulations by Pacifico et al.[21], which estimated that fire O3 reduces GPP by 230 Tg C yr−1 in Amazon forest, this study predicts a lower O3 damage of 137 Tg C yr−1 over the same region (Fig. 4b)
Summary
Fire emissions generate air pollutants ozone (O3) and aerosols that influence the land carbon cycle. Aerosol pollution may promote photosynthesis by enhancing diffuse radiation[16,17], and exert varied impacts on land carbon uptake through concomitant perturbations in meteorology[18,19,20]. Limited studies have accounted for the fire air pollution impacts on regional land carbon assimilation[21,22], and shown that fire O3 and aerosols result in comparable but opposite perturbations in vegetation productivity over the Amazon Forest. The Yale Interactive terrestrial Biosphere (YIBs) model[24], a dynamic global vegetation model, is used to quantify changes in ecosystem GPP due to O3 inhibition and aerosol diffuse fertilization effects (DFE) originating from fire pollution. Joint simulations reveal an indirect terrestrial carbon loss caused by fire air pollutants, because fire O3 strongly dampens ecosystem productivity of unburned forests and masks the benefit of increased diffuse radiation from fire aerosols
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