Articles | Volume 16, issue 7
Atmos. Chem. Phys., 16, 4213–4234, 2016
https://doi.org/10.5194/acp-16-4213-2016
Atmos. Chem. Phys., 16, 4213–4234, 2016
https://doi.org/10.5194/acp-16-4213-2016

Research article 04 Apr 2016

Research article | 04 Apr 2016

Potential sensitivity of photosynthesis and isoprene emission to direct radiative effects of atmospheric aerosol pollution

Susanna Strada1,a and Nadine Unger1 Susanna Strada and Nadine Unger
  • 1School of Forestry and Environmental Studies, Yale University, New Haven, CT, USA
  • anow at: Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France

Abstract. A global Earth system model is applied to quantify the impacts of direct anthropogenic aerosol effective radiative forcing on gross primary productivity (GPP) and isoprene emission. The impacts of different pollution aerosol sources (anthropogenic, biomass burning, and non-biomass burning) are investigated by performing sensitivity experiments. The model framework includes all known light and meteorological responses of photosynthesis, but uses fixed canopy structures and phenology. On a global scale, our results show that global land carbon fluxes (GPP and isoprene emission) are not sensitive to pollution aerosols, even under a global decline in surface solar radiation (direct + diffuse) by  ∼ 9 %. At a regional scale, GPP and isoprene emission show a robust but opposite sensitivity to pollution aerosols in regions where forested canopies dominate. In eastern North America and Eurasia, anthropogenic pollution aerosols (mainly from non-biomass burning sources) enhance GPP by +5–8 % on an annual average. In the northwestern Amazon Basin and central Africa, biomass burning aerosols increase GPP by +2–5 % on an annual average, with a peak in the northwestern Amazon Basin during the dry-fire season (+5–8 %). The prevailing mechanism varies across regions: light scattering dominates in eastern North America, while a reduction in direct radiation dominates in Europe and China. Aerosol-induced GPP productivity increases in the Amazon and central Africa include an additional positive feedback from reduced canopy temperatures in response to increases in canopy conductance. In Eurasia and northeastern China, anthropogenic pollution aerosols drive a decrease in isoprene emission of −2 to −12 % on an annual average. Future research needs to incorporate the indirect effects of aerosols and possible feedbacks from dynamic carbon allocation and phenology.

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Short summary
We apply a global Earth system model to quantify the direct impacts of anthropogenic aerosols on gross primary productivity (GPP) and isoprene emission. On the global scale, GPP and isoprene emission are not sensitive to pollution aerosols, while at the regional scale they show a robust but opposite sensitivity to pollution aerosols. We posit that anthropogenic aerosols affect land carbon fluxes (GPP and isoprene emission) via radiative and thermal mechanisms that vary across regions.
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