| Abstract: |
This project is a continuation of the study of fine aerosol optical properties as a function of aerosol composition and source that was begun in Mexico City in 2003 in collaboration with the MCMA 2003 field study and continued in the Megacity Aerosol Experiment-Mexico City (MAX-Mex) field study during March 2006 sponsored by the U.S. Department of Energy’s Atmospheric Science Program (USDOE/ASP). The objective of this proposed work is to determine aerosol absorption and scattering efficiencies, optical constants (i.e. absorption and scattering coefficients, complex refractive indices, and phase function), and aerosol Ǻngstrom exponents (AE) for absorption (AEA) and scattering (AES) as a function aerosol source, chemical composition, mixing state, chemical aging, and relative humidity (RH). This objective will be accomplished by obtaining in-situ measurements of fine mode aerosol absorption, scattering and total aerosol extinction as a function of wavelength, accompanied by laboratory measurements of aerosol composition and optical properties on fine mode aerosol samples collected simultaneously in the field. In addition, focused laboratory studies of the changes in aerosol optical properties as a function of aerosol composition, mixing state, atmospheric aging processes, and changes in RH will allow for further interpretation of the results observed in the field. The sources of carbonaceous aerosol species will be determined by collaboration with another ASP project (Gaffney, UALR) focused on the use of carbon isotopes (14C and 13C) as aerosol source markers.
This work will complete ongoing laboratory studies of aerosol samples collected during the ASP MAX-Mex and will expand our laboratory efforts to focus on understanding the chemical and physical bases for the aerosol optical properties observed in this important field study. Particular attention will be given to determining the variability of aerosol absorption and evaluation of key chemical species (primary and secondary) leading to this variability. These field and laboratory methods will also be applied in future planned ASP field studies focusing on the direct aerosol radiative effects under clear sky conditions. Obtaining a better understanding of the variability of atmospheric aerosol absorption and scattering as it relates to aerosol chemical properties is a major objective of this project and of the USDOE/ASP. |
