HR: 0800h
AN: A51E-0831    [Abstracts]
TI: Hygroscopicity of Biomass Burning Derived Organic Species Particles
AU: * Chan, M
EM: jtcmn@ust.hk
AF: Environmental Engineering Program, Hong Kong University of Science and Technology, Environmental Engineering Program, School of Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, 852 Hong Kong
AU: Chan, C
EM: keckchan@ust.hk
AF: Department of Chemical Engineering, Hong Kong University of Science and Technology, Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, 852 Hong Kong
AB: Organic species derived from biomass burning can potentially affect the hygroscopicity and cloud condensation activities of aerosols. The hygroscopicity of particles of 3 organic species most commonly detected in biomass burning aerosols (levoglucosan, mannosan, and galactosan) were investigated. The hygroscopic measurements were performed by levitating single particles of roughly 10 microns in diameter in an electrodynamic balance by electric fields and equilibrating the particles at different RH for in situ relative mass determination. Levoglucosan, mannosan, and galactosan particles did not crystallize nor deliquesce. They existed as highly concentrated liquid droplets at low RH, suggesting that biomass burning aerosols may retain water at low RH. These particles show very similar hygroscopic growth and the RH dependence of the Gf, (the ratio of particle diameter equilibrated at a given RH to that at the reference RH (<10%)) can be modeled by Gf = (1-RH/100)^-0.10. Field study has shown that the light scattering coefficient of aged smoke particles was smaller than the young smoke particles. This suggests that the aged smoke particles were less hygroscopic than young smoke particles. This observation may due to the formation of spherical, amorphous carbonaceous particles and the rapid conversion of more hygroscopic potassium chloride in young smoke particles to less hygroscopic potassium sulfate and potassium nitrate in aged smoke particles. In addition, it is possible that levoglucosan can be further converted into more simple organic acids such as C2-C5 dicarboxylic acids, which are generally less hygroscopic with Gf < 1.10 at 85%RH during the initial aging of smoke particle. It is noted that, although malonic acid has Gf = 1.40 at 85%RH, oxalic acid is usually the most abundant dicarboxylic acids detected in biomass burning aerosols and has a Gf = 1.08, which is less hygroscopic than levoglucosan (Gf = 1.21). These hygroscopic results provide additional evidence that aged smoke particles may be less hygroscopic than the fresh smoke particles.
DE: 0305 Aerosols and particles (0345, 4801)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting