Water uptake by biomass burning aerosol at sub- and supersaturated conditions: closure studies and implications for the role of organics

Abstract

Abstract. We investigate the CCN activity of freshly emitted biomass burning particles and their hygroscopic growth at a relative humidity (RH) of 85 %. The particles were produced in the Mainz combustion laboratory by controlled burning of various wood types. The water uptake at sub-and supersaturations is parameterized by the hygroscopicity parameter, κ (c.f. Petters and Kreidenweis, 2007). For the wood burns, κ is low, generally around 0.06. The main emphasis of this study is a comparison of κ derived from measurements at sub-and supersaturated conditions (κ G and κ CCN ), in order to see whether the water uptake at 85 % RH can predict the CCN properties of the biomass burning particles. Differences in κ G and κ CCN can arise through solution nonidealities, the presence of slightly soluble or surface active compounds, or non-spherical particle shape. We find that κ G and κ CCN agree within experimental uncertainties (of around 30 %) for particle sizes of 100 and 150 nm; only for 50 nm particles is κ CCN larger than κ G by a factor of 2. The magnitude of this difference and its dependence on particle size is consistent with the presence of surface active organic compounds. These compounds mainly facilitate the CCN activation of small particles, which form the most concentratedCorrespondence to: U. Dusek (u.dusek@uu.nl) solution droplets at the point of activation. The 50 nm particles, however, are only activated at supersaturations higher than 1 % and are therefore of minor importance as CCN in ambient clouds. By comparison with the actual chemical composition of the biomass burning particles, we estimate that the hygroscopicity of the water-soluble organic carbon (WSOC) fraction can be represented by a κ WSOC value of approximately 0.2. The effective hygroscopicity of a typical wood burning particle can therefore be represented by a linear mixture of an inorganic component with κ ∼ = 0.6, a WSOC component with κ ∼ = 0.2, and an insoluble component with κ = 0.

Experimentally measured morphology of biomass burning aerosol and its impacts on CCN ability

“…The previous work of Dusek et al (2011) has investigated conceptually the importance of fractal morphology in CCN analysis. We present experimental data for both the hygroscopicity and morphology of the particle and apply it to κ-Köhler analysis.…”

“…Both this work and Martin et al observed the effect that aging has on particle morphology and how that impacts κ, but here we are able to quantify the changes in morphology through empirical constructs such as fractal-like dimension. It remains that the magnitude of particle nonsphericity and its effect on hygroscopicity has only been theoretically manipulated and not experimentally measured, especially as a function of particle aging (Dusek et al, 2011). Here we provide simultaneous morphological and hygroscopicity measurements of fresh and aged biomass aerosol.…”

Water uptake by fresh Indonesian peat burning particles is limited by water-soluble organic matter

“…Water uptake properties of biomass burning particles, including those emitted from peatlands, have been explored in a laboratory through measurements of hygroscopic growth and CCN activity (Chand et al, 2005;Dusek et al, 2005Dusek et al, , 2011Day et al, 2006;Petters et al, 2009;Carrico et al, 2010). In general, freshly emitted biomass burning particles have been found to be hygroscopic.…”

Hygroscopicity of organic compounds from biomass burning and their influence on the water uptake of mixed organic ammonium sulfate aerosols

“…The annual globally burned land area is in the range of 3 to 3.5 million square kilometers, resulting in emissions amounting to 2.5 × 10 9 kg carbon per year (van der Werf et al, 2006;Schultz et al, 2008). Particles in biomass burning smoke enriched with hygroscopic organic and inorganic constituents are suggested to act as efficient cloud condensation nuclei (Novakov and Corrigan, 1996;Petters et al, 2009;Rissler et al, 2010;Dusek et al, 2011;Frosch et al, 2011). In the Amazon basin, for example, the CCN concentration in the dry season is 1 order of magnitude higher than in the wet season due to biomass burning (Roberts et al, 2001;Carrico et al, 2008;Hening et al, 2010).…”