Articles | Volume 9, issue 22
Atmos. Chem. Phys., 9, 8949–8966, 2009
Atmos. Chem. Phys., 9, 8949–8966, 2009

  27 Nov 2009

27 Nov 2009

Reduction in biomass burning aerosol light absorption upon humidification: roles of inorganically-induced hygroscopicity, particle collapse, and photoacoustic heat and mass transfer

K. A. Lewis1, W. P. Arnott1, H. Moosmüller2, R. K. Chakrabarty2, C. M. Carrico3, S. M. Kreidenweis3, D. E. Day4, W. C. Malm4, A. Laskin5, J. L. Jimenez6, I. M. Ulbrich6, J. A. Huffman6,*, T. B. Onasch7, A. Trimborn7, L. Liu8, and M. I. Mishchenko8 K. A. Lewis et al.
  • 1Department of Physics, University of Nevada, Reno, NV 89557, USA
  • 2Division of Atmospheric Sciences, Desert Research Institute, Nevada, System of Higher Education, Reno, NV 89512, USA
  • 3Department of Atmospheric Science, Colorado State University, Ft. Collins, CO 80523, USA
  • 4Cooperative Institute for Research of the Atmosphere/National Park Service, Colorado State University, Ft. Collins, CO 80523, USA
  • 5William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA
  • 6Department of Chemistry and Biochemistry and Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado at Boulder, Boulder, CO 80309, USA
  • 7Aerodyne Research Inc., Center of Aerosol and Cloud Chemistry, Billerica, Massachusetts 01821, USA
  • 8NASA Goddard Institute for Space Studies, New York, NY 10025, USA
  • *now at: Max Planck Institute for Chemistry, Mainz, Germany

Abstract. Smoke particle emissions from the combustion of biomass fuels typical for the western and southeastern United States were studied and compared under high humidity and ambient conditions in the laboratory. The fuels used were Montana ponderosa pine (Pinus ponderosa), southern California chamise (Adenostoma fasciculatum), and Florida saw palmetto (Serenoa repens). Information on the non-refractory chemical composition of biomass burning aerosol from each fuel was obtained with an aerosol mass spectrometer and through estimation of the black carbon concentration from light absorption measurements at 870 nm. Changes in the optical and physical particle properties under high humidity conditions were observed for hygroscopic smoke particles containing substantial inorganic mass fractions that were emitted from combustion of chamise and palmetto fuels. Light scattering cross sections increased under high humidity for these particles, consistent with the hygroscopic growth measured for 100 nm particles in HTDMA measurements. Photoacoustic measurements of aerosol light absorption coefficients revealed a 20% reduction with increasing relative humidity, contrary to the expectation of light absorption enhancement by the liquid coating taken up by hygroscopic particles. This reduction is hypothesized to arise from two mechanisms: (1) shielding of inner monomers after particle consolidation or collapse with water uptake; (2) the lower case contribution of mass transfer through evaporation and condensation at high relative humidity (RH) to the usual heat transfer pathway for energy release by laser-heated particles in the photoacoustic measurement of aerosol light absorption. The mass transfer contribution is used to evaluate the fraction of aerosol surface covered with liquid water solution as a function of RH.

Final-revised paper