Physical and Chemical Properties of Laboratory and Ambient Aerosols Related to Climate Change

123 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2003.This study summarizes the evaluation of closure when measuring and modeling aerosol optical properties as a function of RH in a laboratory and reports measured ambient aerosol optical and chemical properties for an anthropogenically perturbed continental US site from 1995 to 2000. The optical closure experiment was completed in a laboratory set-up for NaCl, (NH4)2SO 4 and NH4NO3 aerosol using an RH scanning nephelometry system. Correcting for nephelometer non-idealities and RH of the sample improved the agreement between measured and predicted total scattering coefficients (sigmasp) at RH = 80% from 35% to 11%. The closure experiment revealed the importance of keeping the nephelometry system isothermal when measuring particle scattering coefficients as a function of RH or as particles exist in the ambient environment. Corrections based on the laboratory results were applied to ambient optical measurements. The averaged hygroscopic growth factor (f(RH = 82%)) at 550 nm was 1.74 +/- 0.31 for sub-micrometer particles for the site. Chemical analysis of submicrometer particles revealed that approximately 50% of the ambient aerosol mass was SO4 and NH4. Direct aerosol radiative forcing (DARF) for the site was estimated to be -1.3 W/m2 at an ambient RH of 72%. Therefore the net effect of ambient aerosols at the site is to cool the atmosphere.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD