Impact of biomass burning aerosols on regional climate over Southeast USA

Great interest has been aroused in how important aerosols may play a role in the cooling of the southeastern USA. A major contributor to the particulate matters over this region is biomass burning. Studies have found that for biomass burning aerosols, there is significant suppression of water uptake at sub-saturated RH, but enhanced CCN activity. In other words, they are relatively non-hygroscopic but yet are CCN active. In addition, the CCN activity changes as the particles age.

In order to better describe the CCN activation of biomass burning aerosols, in this study, we are to implement in WRF the cloud droplet activation parameterization of Kumar et al.(2009), which considers the competition between soluble and in soluble aerosols for water vapor during cloud droplet formation in ascending air parcels, so that the CCN activity evolution with time and composition can be captured. The water uptake properties of the biomass burning aerosol are constrained using observations of fresh and aged biomass burning aerosol sampled during the 2008 ARctas campaign (Jacob et al., 2010).

Further, we are to employ the coupled WRF-CMAQ (Wong et al., 2012) in order to accounting for the feedback of direct effect from gases and aerosols. By comparing the results from WRF and coupled WRF-CMAQ, we are interested in to what extent, the climate (especially, temperature, cloud coverage and precipitation) of the southeastern region will be affected by direct effects of the biomass burning aerosols.

Finally, for the coupled WRF-CMAQ, we want to take into account the feedback by indirect effect as well. To achieve this goal, we plan to couple the CCN activation parameterization mentioned before with CMAQ. Hence, we are able to have a comprehensive estimate of the impact of biomass burning aerosols on the regional climate through direct and indirect effects.

References:

Kumar, P., Sokolik, I.N., and Nenes, A. (2009) Parameterization of Cloud Droplet Formation for Global and Regional models: Including Adsorption Activation from Insoluble CCN., Atmos. Chem. Phys., 9, 2517-2532

Jacob, D. J., Crawford, J. H., Maring, H., Clarke, A. D., Dibb, J. E., Emmons, L. K., Ferrare, R. A., Hostetler, C. A., Russell, P. B., Singh, H. B., Thompson, A. M., Shaw, G. E., McCauley, E., Pederson, J. R., and Fisher, J. A. (2010): The Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission: design, execution, and first results, Atmos. Chem. Phys., 10, 5191-5212, doi:10.5194/acp-10-5191-2010

Wong D, Pleim J, Kang D, et al, (2012): WRF-CMAQ two-way coupled system with aerosol feedback: software development and preliminary results. Geoscientific Model Development , 5,299-312,doi: 10.5194/gmd-5-299-2012