Particulate contributions to light extinction and local forcing at a rural Illinois site |
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| Institution: | 1. European Commission, Joint Research Centre, Ispra, Italy;2. NASA, Goddard Space Flight Center, Greenbelt, MD, USA;1. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA;2. Environmental Earth and Ocean Sciences, University of Massachusetts, Boston, MAUSA;3. Ocean Sciences Department, University of California Santa Cruz, Santa Cruz, CA 95064, USA;4. Facultad de Ciencias del Mar, Universidad Autónoma de Sinaloa, Mazatlán, Sinaloa, Mexico;1. Instituto Nacional de Pesquisas Espaciais, Avenida dos Astronautas, 1758 São José dos Campos, São Paulo, Brazil;2. Scripps Institution of Oceanography, University of California San Diego, La Jolla Shores Drive, La Jolla, CA 92037, USA;3. Laboratoire d''Océanologie et de Géosciences, Université du Littoral-Côte d''Opale, 32 Avenue Foch, 62930 Wimereux, France;1. European Commission, Joint Research Centre, Ispra, Italy;2. Physics Department, University of Miami, Coral Gables, FL, USA;3. Sensor Science Division, National Institute of Standards and Technology, Gaithersburg, MD, USA;4. National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, MD, USA;5. EUMETSAT, Remote Sensing and Products Division, Darmstadt, Germany;6. European Space Agency, Noordwijk, The Netherlands;7. National Oceanic and Atmospheric Administrations, Center for Satellite Applications and Research, College Park, MD, USA;8. Sorbonne Universités, Université Pierre et Marie Curie, Paris 06, UMR 7093, Laboratoire d''Océanographie de Villefranche, Villefranche-sur-Mer, France;9. Department of Imaging and Applied Physics, Remote Sensing and Satellite Research Group, Curtin University, Perth, WA, Australia |
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| Abstract: | The light extinction and direct forcing properties of the atmospheric aerosol were investigated for a midwestern rural site (Bondville, IL) using field measurements, a semi-empirical light extinction model, and a radiative transfer code. Model inputs were based on the site measurements of the physical and chemical characteristics of atmospheric aerosol during the spring, summer, fall and winter of 1994. The light scattering and extinction coefficients were calculated and apportioned using the elastic light scattering interactive efficiency (ELSIE) model (Sloane and Wolff, 1985, Atmospheric Environment 19(4), 669–680). The average efficiencies calculated for organic carbon (OC, carbon measured as organic multiplied by 1.2) ranged from 3.81 m2/g OC at lower relative humidities (<63%) to 6.90 m2/g OC at higher relative humidities (>75%) while sulfate (assumed as ammonium sulfate) efficiencies ranged from 1.23 m2/g (NH4)2SO4 to 5.78 m2/g (NH4)2SO4 for the same range of relative humidities. Radiative transfer calculations showed that the rural aerosol at Bondville is most likely to have an overall negative (cooling) forcing effect on climate. Elemental carbon (EC), however, acts to counter sulfate forcing to a degree that has a significant seasonal variation, primarily due to the seasonal variation in the sulfate concentrations. Taking the loading to be the mean summer EC+ammonium sulfate loading and assuming EC]/(NH4)2SO4] to be zero in one case (i.e. no soot present) and 0.025 (summer mean at Bondville) in another leads to a 37% difference in calculated forcing. |
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