Distinguishing the impacts of natural and anthropogenic aerosols on global gross primary productivity through diffuse fertilization effect.

Aerosols can enhance ecosystem productivity by increasing diffuse radiation. Such diffuse fertilization effects (DFEs) vary among different aerosol compositions and sky conditions. Here, we apply a suite of chemical, radiation, and vegetation models in combination with ground- and satellite-based measurements to assess the impacts of natural and anthropogenic aerosol species on gross primary productivity (GPP) through DFE during 2001-2014. Globally, aerosols increase GPP by 8.9 Pg C yr^-1 at clear skies but only 0.95 Pg C yr^-1 at all skies. Anthropogenic aerosols account for 41% of the total GPP enhancement though they contribute only 25% to the increment of diffuse radiation. Sulfate/nitrate aerosols from anthropogenic sources make dominant contributions of 33% (36%) to aerosol DFE at all (clear) skies, followed by the ratio of 18% (22%) by organic carbon aerosols from natural sources. In contrast to other species, black carbon aerosols decrease global GPP by 0.28 (0.12) Pg C yr^-1 at all (clear) skies. Long-term simulations show that aerosol DFE is increasing 2.9% yr^-1 at all skies mainly because of a downward trend in cloud amount. This study suggests that the impacts of aerosols and cloud should be considered in projecting future changes of ecosystem productivity under varied emission scenarios. [ABSTRACT FROM AUTHOR]