Impact of Aerosols From Urban and Shipping Emission Sources on Terrestrial Carbon Uptake and Evapotranspiration: A Case Study in East Asia

Abstract

This study quantifies the immediate influences of aerosols from urban anthropogenic and shipping emission sources on carbon and water fluxes in East Asia on a cloudy day in spring 2016 when strong regional pollution transport occurred and intensive field campaign measurements are available. Within National Aeronautics and Space Administration (NASA)'s Land Information System (LIS), a long-term offline Noah-multiparameterization (MP) simulation with dynamic vegetation is performed. Modeled soil moisture and leaf area index are evaluated with satellite observations to ensure that land surface conditions are moderately well reproduced. The LIS output is then used to initialize several coupled NASA-Unified Weather Research and Forecasting model simulations with online chemistry in which urban anthropogenic and shipping emissions are (1) largely based on the Hemispheric Transport of Air Pollution Phase 2 inventory for 2010, (2) reduced by 20% and 50% for all chemical species, and (3) adjusted only for nitrogen oxides (NOx) using satellite observations. Overall, modeled gross primary productivity and evapotranspiration almost linearly increase with the all-species emission reductions, but their responses to emission-induced aerosol optical depth (AOD) changes show strong spatial variability resulting from combined radiation and temperature impacts. Using satellite-observation-constrained NOx emissions, modeled nitrogen species and AOD better match various measurements at some locations/times. All-species and NOx-only emission adjustments lead to different gross primary productivity and evapotranspiration changes with AOD, especially over South Korea. This study demonstrates the importance of accurately quantifying emission impacts on atmosphere-biosphere interactions. Improving more species' emission inputs for Earth system models, including applying effective chemical data assimilation methods, is strongly encouraged.