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Simulating Changes in Tropospheric Aerosol Burden and its Radiative Effects across the Northern Hemisphere: Contrasting Multi-Decadal Trends between Asia and North America
Citation:
Mathur, R., J. Xing, Jon Pleim, David-C Wong, C. Hogrefe, M. Gan, AND C. Wei. Simulating Changes in Tropospheric Aerosol Burden and its Radiative Effects across the Northern Hemisphere: Contrasting Multi-Decadal Trends between Asia and North America. AGU Meeting, San Francisco, CA, December 15 - 19, 2014.
Impact/Purpose:
The National Exposure Research Laboratory's (NERL's) Atmospheric Modeling and Analysis Division (AMAD) conducts research in support of EPA's mission to protect human health and the environment. AMAD's research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the Nation's air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Description:
Though aerosol radiative effects have been recognized as some of the largest sources of uncertainty among the forcers of climate change, the verification of the spatial and temporal variability of the magnitude and directionality of aerosol radiative forcing has remained challenging. Significant and contrasting changes in tropospheric aerosol burden 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% & 50%, respectively. In contrast, anthropogenic emissions have increased dramatically across Asia. These changes provide an opportunity for conducting a systematic investigation of the processes regulating aerosol distributions, their optical properties, and verification of their simulated radiative effects for past conditions relative to measurements. We conduct multi-decadal simulations for the 1990-2010 period with the two-way coupled WRF-CMAQ modeling system over a domain covering the northern hemisphere and a nested finer resolution continental U.S. domain. Simulated aerosol size and 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 (aerosol burden and composition, radiation, temperature) over North America and Asia are analyzed in conjunction surface, aloft and remote sensing measurements to contrast the differing trends in aerosol-radiation interactions in these regions over the past two decades. Both model and measurements indicate significant reductions in tropospheric aerosol burden across North America and an associated increase in shortwave radiation at the surface. In contrast, an increase in tropospheric aerosol burden and reduction in surface shortwave radiation in noted across large portions of Asia during the past two decades. Simulated trends in aerosol composition, tropospheric burden, and radiative effects are compared with those inferred from available measurements. Model simulations with and without aerosol radiative effects are analyzed to assess the impacts of these interactions on severity of air pollution episodes.
