Evaluating the impact of urban and shipping emissions on aerosol pollution, vegetation photosynthesis and transpiration: a satellite-constrained modeling study with policy implications

Using the NASA-Unified Weather Research and Forecasting with online Chemistry (NUWRF-Chem), we evaluate the impact of urban anthropogenic and shipping emissions on aerosol pollution during the Korea-US Air Quality field study (KORUS-AQ) period in spring 2016. We also evaluate the immediate influences of aerosols from these emission sources on vegetation photosynthesis and transpiration. Within NASA's Land Information System (LIS), a long-term offline Noah-MP simulation with dynamic vegetation is performed. Modeled soil moisture and leaf area index are evaluated with observations from the Soil Moisture Active-Passive and the Moderate Resolution Imaging Spectroradiometer, respectively, to ensure that land surface conditions are moderately well reproduced. The LIS output is then used to initialize several NUWRF-Chem simulations in which urban anthropogenic and shipping emissions are: 1) largely based on the Hemispheric Transport of Air Pollution Phase 2 inventory; 2) reduced from 1) by 20% and 50% for all chemical species; and 3) adjusted only for nitrogen oxides (NO_x) using satellite observations. Overall, modeled gross primary productivity (GPP) and evapotranspiration (ET) 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. After adjusting NO_x emissions with satellite observations, modeled nitrogen species and aerosols better match various measurements (e.g., from the DC-8 aircraft, the R/V Onnuri ship, the Aerosol Robotic Network, and the Geostationary Ocean Color Imager) at some locations/times. All-species and NO_x-only emission adjustments lead to different GPP and ET changes with AOD.

This study demonstrates the importance of accurate emission inputs to simulating aerosols as well as quantifying its impact on atmosphere-biosphere interactions. Improving more species' emission inputs for Earth system models, including assimilating satellite and other observations, is strongly encouraged. We also discuss the policy implications of this work, related to the co-impacts/co-benefits of controlling anthropogenic emissions for air quality, climate, human and vegetation health.