Aerosols — fine particles and droplets suspended in the atmosphere — scatter incoming solar radiation. This light diffusion effect can help plants to increase their photosynthetic efficiency, which has implications for ecosystem carbon dynamics. Human activities that increase aerosol loads, such as deforestation fires, can therefore increase net primary productivity — this effect might be worth including in carbon accounting.
Alexandru Rap, from the University of Leeds, and co-workers investigate the effect of aerosol emissions from biomass burning across Amazonia during 1998–2007. They find that these emissions increase mean diffuse radiation by 3.4–6.8% and net primary production by 1.4–2.8%. This increase in primary production might seem modest but they calculate that it offsets the equivalent of 33–65% of the annual regional carbon emissions from biomass burning. The enhancement of primary production occurred during the dry season, counteracting some of the negative effects of drought on tropical forest growth.
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Brown, A. Firing photosynthesis. Nature Clim Change 5, 718 (2015). https://doi.org/10.1038/nclimate2748