The general seasonal climatology and chemical composition of Arctic aerosol are basically well understood, but the contribution from organic compounds is not. At lower latitudes, organics are known to play a large role in climate forcing. The direct radiative effects of aerosol on Arctic climate have been identified, but our knowledge of indirect effects (via cloud microphysical interactions) is still incomplete. In particular, further understanding is needed of the processes through which aerosols serve as cloud condensation nuclei and enhance the reflectivity of low-level water clouds, a phenomenon known as the first aerosol indirect effect.
Funds are provided to carry out a sampling program at Barrow, Alaska, to determine the fraction of Arctic aerosol that is organic, throughout the year, and identify functional group composition, possible anthropogenic sources, and to provide a basis for rigorous incorporation of Arctic aerosol chemical composition in climate change studies. The principal investigators will deploy a new shortwave spectroradiometer at Barrow, covering the wavelength range 0.35 - 2.5 microns, which will provide high-time-resolution data for retrieval of cloud thermodynamic phase, liquid/ice water path, and effective particle radius. With supplemental data from the U.S. Department of Energy Atmospheric Radiation Measurement Program site at Barrow, they will thus be able to quantify the shortwave component of the first aerosol indirect effect and, through the new understanding they will gain about organics, understand both liquid water path and effective radius contributions to the first aerosol indirect effect.
