You are here:
Simulating Changes in Tropospheric Composition, Aerosol Radiative Effects, and Atmospheric Deposition across the Northern Hemisphere: Contrasting Multi-Decadal Trends between Asia and North America
Citation:
Mathur, R., C. Hogrefe, Jon Pleim, David-C Wong, J. Xing, AND Y. Zhang. Simulating Changes in Tropospheric Composition, Aerosol Radiative Effects, and Atmospheric Deposition across the Northern Hemisphere: Contrasting Multi-Decadal Trends between Asia and North America. 2018 Joint International Conference on ABaCAS and CMAS-Asia-Pacific, Beijing, CHINA, May 21 - 23, 2018.
Impact/Purpose:
Significant and contrasting changes in tropospheric composition across the Northern hemisphere have occurred over the past two decades as a result of changing patterns of emissions of primary aerosol and gaseous precursors. During this period, SO2 and NOx emissions across the US have reduced by about 66% and 50%, respectively. In contrast, anthropogenic emissions have increased dramatically across many parts of Asia. Detailed simulations with the WRF-CMAQ modeling system for the 1990-2010 period quantitatively demonstrate the impact of emission reductions in the U.S. on improving air quality, reducing population exposure to air pollution, and reducing atmospheric deposition of nutrients and acidic substances to sensitive ecosystems. The reduction in tropospheric aerosol burden also helps reduce aerosol cooling that increases atmospheric ventilation thereby further reducing surface air pollution. In contrast rising emissions in many parts of Asia during this period, increased regional tropospheric aerosol burden, stabilized the atmosphere and further exacerbated surface air pollution. Model results also show that the exceedance of critical load thresholds has decreased at many locations in North America and Europe, but has increased in Asia over the past two decades as a result of contrasting trends in atmospheric nitrogen and sulfur emissions.
Description:
Significant and contrasting changes in tropospheric composition across the Northern hemisphere have occurred over the past two decades as a result of changing patterns of emissions of primary aerosol and gaseous precursors. During this period, SO2 and NOx emissions across the US have reduced by about 66% and 50%, respectively. In contrast, anthropogenic emissions have increased dramatically across many parts of Asia. These changes provide an opportunity for conducting a systematic investigation of processes regulating aerosol composition and optical properties, the interactions between atmospheric chemistry and dynamics, and assessing the ability of models to capture these changes in the state of the atmosphere relative to historical measurements. We conducted multi-decadal simulations for the 1990-2010 period with the two-way coupled WRF-CMAQ modeling system over a domain covering the Northern hemisphere. Simulated aerosol composition and size are used to estimate their optical properties which are then used in the radiation calculations impacting both photolysis rates and atmospheric dynamics. Model results (tropospheric composition, radiation, deposition amounts) over North America and Asia are analyzed in conjunction surface, aloft and remote sensing measurements to contrast the differing trends in these regions over the past two decades. Model simulations with and without aerosol radiative effects are analyzed to assess the impacts of these interactions on severity of air pollution episodes. Additionally, changing emissions patterns of NOx, SO2, and NH3 have likely altered both their atmospheric transport distances as well as deposition patterns and amounts and thus analysis is also conducted to examine the impacts of contrasting changes in historical emission patterns (reductions in North America and Europe vs. increases across regions in Asia), on changing deposition amounts to terrestrial and aquatic ecosystems in these regions.
