Investigation of multi-decadal trends in aerosol direct radiative effect from anthropogenic emission changes over North America and North Hemisphere by using a multiscale two-way coupled WRF-CMAQ mode

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Description

Anthropogenic aerosols play a dominant role in “global dimming or brightening”. However, aerosol radiative effects are still recognized as some of the largest sources of uncertainty among the forcers of climate change. This study will systematically investigate changes in anthropogenic emissions of short-lived aerosol precursors over the past two decades (1990–2010) in the Northern Hemisphere (especially in the United States), their impacts on aerosol loading, and subsequent impacts on regional radiation budgets. The hypothesis that changes in surface solar radiation over time are caused by the changing patterns of anthropogenic emissions of aerosols and aerosol precursors will be tested in this study. A new two-way coupled meteorology and atmospheric chemistry model composed of the Weather Research and Forecast (WRF) model and the Community Multiscale Air Quality (CMAQ) model has been developed by the U.S. Environmental Protection Agency. This two-way model is being run for 20 years (1990–2010) on both a 12-km resolution grid that covers most of North America and a 108-km resolution domain for the Northern Hemisphere. A newly developed 20-year U.S. emission inventory is used in order to accurately reflect the emission trends resulting from progressively more stringent air quality regulations as well as population trends, economic conditions, and technology changes in motor vehicles and electric power generation. Global data sets are used for the emissions outside the U.S. The direct effects of aerosols on shortwave radiation are considered in this WRF/CMAQ model. New algorithms on the calculation of aerosol optical properties and radiation have been developed for considering of both computational efficiency and more realistic aerosol states. Preliminary model simulations for 1990 and 2006 are being evaluated both for their performance in comparison to observed concentrations and simulation of observed trends (details about observations are reported in the poster by Gan et al.) in concentrations and surface radiation. Aerosol mixing state is a key factor for the calculations of aerosol optical properties. A more realistic core-shell model will be tested to demonstrate the uncertainties on the treatment of aerosols in this study. Different nudging strategies on atmosphere and soil will be compared in sensitivity studies in order to get a balance between strong signal of aerosol effects and good model performance.