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Interaction among aerosols, clouds and terrestrial carbon uptake

(left) Radiation use efficiencies and (right) carbon uptake fluxes as a function of TI during the summer season (JJA) from 1992 to 2004 for four WVPD bins: blue, red, orange, and green dots represent data with ranges of WVPD of 0 hPa < WVPD < 4 hPa, 4 hPa _ WVPD < 12 hPa, 12 hPa _ WVPD < 16 hPa, and WVPD _ 16 hPa, respectively. The corresponding color lines are a linear regression for RUE and a quadratic regression for maximum carbon uptake for various WVPD ranges. The dashed-black line in right plot shows the best fit of CO2 uptake flux for all WVPD conditions. (Min and Wang 2008)


Photosynthetically active radiation (PAR) is a fundamental variable affecting carbon uptake by ecosystems, not only the total amount but also its spectral distribution and its partitioning between direct and diffuse components. These aspects of PAR are strongly affected by clouds and aerosols.
Clouds and aerosols may enhance diffuse PAR, or, in the case of optically thick clouds, they may reflect most of the irradiance out of the atmosphere. Ecosystems, in turn, affect both cloud formation through the process of evapotranspiration and cloud properties by influencing aerosol and water vapor concentrations.
We studied the interactions among aerosols, clouds and terrestrial carbon uptake:

Impacts of aerosols and clouds on forest-atmosphere carbon exchange (2005)

Clouds modulate terrestrial carbon uptake in a midlatitude hardwood forest (2008)