Cloud condensation nuclei activity of fresh primary and aged biomass burning aerosol 1Center for Atmospheric Particle Studies, Carnegie Mellon University, Pennsylvania, 15217, Pittsburgh, USA
13 Aug 2012
2Department of Chemical Engineering, University of Patras, Patra, Greece
3Institute of Chemical Engineering Sciences, Foundation of Research & Technology, Patra, Greece
Received: 20 February 2012 – Published in Atmos. Chem. Phys. Discuss.: 16 March 2012 Abstract. We quantify the hygroscopic properties of particles freshly emitted from
biomass burning and after several hours of photochemical aging in a smog
chamber. Values of the hygroscopicity parameter, κ, were calculated
from cloud condensation nuclei (CCN) measurements of emissions from
combustion of 12 biomass fuels commonly burned in North American wildfires.
Prior to photochemical aging, the κ of the fresh primary aerosol
varied widely, between 0.06 (weakly hygroscopic) and 0.6 (highly
hygroscopic). The hygroscopicity of the primary aerosol was positively
correlated with the inorganic mass fraction of the particles. Photochemical
processing reduced the range of κ values to between 0.08 and 0.3.
The changes in κ were driven by the photochemical production of
secondary organic aerosol (SOA). SOA also contributed to growth of particles
formed during nucleation events. Analysis of the nucleation mode particles
enabled the first direct quantification of the hygroscopicity parameter
κ for biomass burning SOA, which was on average 0.11, similar to
values observed for biogenic SOA. Although initial CCN activity of biomass
burning aerosol emissions are highly variable, after a few hours of
photochemical processing κ converges to a value of 0.2 ± 0.1.
Therefore, photochemical aging reduces the variability of biomass burning CCN κ,
which should simplify analysis of the potential effects of biomass
burning aerosol on climate.
Revised: 25 July 2012 – Accepted: 25 July 2012 – Published: 13 August 2012
Citation: Engelhart, G. J., Hennigan, C. J., Miracolo, M. A., Robinson, A. L., and Pandis, S. N.: Cloud condensation nuclei activity of fresh primary and aged biomass burning aerosol, Atmos. Chem. Phys., 12, 7285-7293, doi:10.5194/acp-12-7285-2012, 2012.