Abstract
Abstract. This study examines the morphological properties of freshly emitted and atmospherically aged aerosols from biomass burning. The impacts of particle morphology assumptions on hygroscopic predictions are examined. Chamber experiments were conducted at the University of California, Riverside, Center for Environmental Research and Technology (CE-CERT) atmospheric processes lab using two biomass fuel sources: manzanita and chamise. Morphological data was obtained through the use of an aerosol particle mass analyzer (APM), scanning mobility particle sizer (SMPS) system and transmission electron microscope (TEM). Data from these instruments was used to calculate both a dynamic shape factor and a fractal-like dimension for the biomass burning emissions. This data was then used with κ-Köhler theory to adjust the calculated hygroscopicity for experimentally determined morphological characteristics of the aerosol. Laboratory measurement of biomass burning aerosol from two chaparral fuels show that particles are nonspherical with dynamic shape factors greater than 1.15 for aerosol sizes relevant to cloud condensation nuclei (CCN) activation. Accounting for particle morphology can shift the hygroscopicity parameter by 0.15 or more. To our knowledge, this work provides the first laboratory chamber measurements of morphological characteristics for biomass burning cloud condensation nuclei and provides experimental particle shape evidence to support the variation in reported hygroscopicities of the complex aerosol.
Highlights
Aerosols have important health effects, affect regional visibility, are a key factor in the earth’s climate via radiative forcing mechanisms, and play a vital role in atmospheric chemistry (Seaton et al, 1995; Haywood and Boucher, 2000; Ramanathan et al, 2001; Pöschl, 2005; Forster et al, 2007)
Through two independent measurements that particles emitted from biomass combustion are not spherical and that the degree of nonsphericity can change with photochemical exposure
For biomass burning aerosol sampled near source with electrical mobility techniques, size and volume measurements are likely overestimated
Summary
Aerosols have important health effects, affect regional visibility, are a key factor in the earth’s climate via radiative forcing mechanisms, and play a vital role in atmospheric chemistry (Seaton et al, 1995; Haywood and Boucher, 2000; Ramanathan et al, 2001; Pöschl, 2005; Forster et al, 2007). Particles are ubiquitous but can be nonuniform and nonspherical. A number of instruments exist to measure these critical aerosol properties. One property that remains difficult to characterize through conventional techniques is particle morphology. Morphology is used here as a term to describe the shape of a 3-dimensional particle and has a direct impact on particle size measurements (DeCarlo et al, 2004). The true volume of a particle is difficult to accurately measure without knowledge of the particle morphology. Reducing uncertainties in particle morphology will increase the accuracy of characterizations and parameterizations that rely on knowing the true volume of a particle, e.g., particle density and hygroscopicity
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