Aerosol pollution radiative effects on land carbon uptake in China

Xu Yue, Nadine Unger
2016 Atmospheric Chemistry and Physics Discussions  
China suffers from frequent haze pollution episodes that alter the surface solar radiation and influence regional carbon uptake by the land biosphere. Here, we apply combined vegetation and radiation modeling and multiple observational datasets to assess the radiative effects of aerosol pollution in China on the regional land carbon uptake for the 2009–2011 period. First, we assess the inherent sensitivity of China's land biosphere to aerosol pollution by defining and calculating two
more » ... erosol optical depth (AOD) at 550&amp;thinsp;nm thresholds (i) AOD<sub>t1</sub>, resulting in the maximum net primary productivity (NPP), and (ii) AOD<sub>t2</sub>, such that if local AOD&amp;thinsp;<&amp;thinsp;AOD<sub>t2</sub>, the aerosol DFE always promotes local NPP compared with aerosol-free conditions. Then, we apply the thresholds, satellite data, and interactive vegetation modeling to estimate current impacts of aerosol pollution on land ecosystems. In the Northeast, observed AOD is 55&amp;thinsp;% lower than AOD<sub>t1</sub>, indicating strong aerosol DFE on local NPP. In the southeastern coastal regions, observed AOD is close to AOD<sub>t1</sub>, suggesting that regional NPP is promoted by the current level of aerosol loading but that further increases in AOD in this region will weaken the fertilization effects. The North China Plain experiences limited enhancement of NPP by aerosols because observed AOD is 77&amp;thinsp;% higher than AOD<sub>t1</sub> but 14&amp;thinsp;% lower than AOD<sub>t2</sub>. Aerosols always inhibit regional NPP in the Southwest because of the persistent high cloud coverage that already substantially reduces the total light availability there. Under clear-sky conditions, simulated NPP shows widespread increases of 20&amp;ndash;60&amp;thinsp;% (35.0&amp;thinsp;&amp;plusmn;&amp;thinsp;0.9&amp;thinsp;% on average) by aerosols. Under all-sky conditions, aerosol pollution has spatially contrasting opposite sign effects on NPP from &amp;minus;3&amp;thinsp;% to +6&amp;thinsp;% (1.6&amp;thinsp;&amp;plusmn;&amp;thinsp;0.5&amp;thinsp;% on average), depending on the local AOD relative to the regional thresholds. Stringent aerosol pollution reductions motivated by public health concerns, especially in the North China Plain and the Southwest, will help protect land ecosystem functioning in China and mitigate long-term global warming.
doi:10.5194/acp-2016-899 fatcat:dxp4ueu34jhddckavhnorldsn4