You are here:
Effect of the secondary organic aerosol coatings on black carbon water uptake, cloud condensation nuclei activity, and particle collapse
Citation:
Holder, A., S. Suda, G. Hagler, M. Hays, AND M. Petters. Effect of the secondary organic aerosol coatings on black carbon water uptake, cloud condensation nuclei activity, and particle collapse. American Geophysical Union Fall Meeting, San Francisco, CA, December 03 - 07, 2012.
Impact/Purpose:
The purpose of this work is to relate the ability of black carbon to take up water with its mixing state. The hygroscopic behavoir of black carbon will directly affect its lifetime in the atmosphere and impact on cloud formation.
Description:
The ability of black carbon aerosols to absorb water and act as a cloud condensation nuclei (CCN) directly controls their lifetime in the atmosphere as well as their impact on cloud formation, thus impacting the earth’s climate. Black carbon emitted from most combustion processes is initially hydrophobic, thus requiring high critical supersaturations before these particles can serve as CCN. Due to atmospheric processing, black carbon particles can become internally mixed with hydrophilic material, altering the water uptake and CCN properties of the particle. We simulated this process by coating flame-generated black carbon particles with secondary organic aerosol produced from the reaction of decane and toluene with OH, and β-caryophyllene with O3 in the presence of an OH scavenger. Particle coating thickness was determined by tandem differential mobility analysis. Hygroscopic properties of the coated particles were assessed using a hygroscopicity tandem differential mobility analyzer (HTDMA) operated at RH ~98% and a CCN counter. Additionally, a Single Particle Soot Photometer (SP2) was used to measure the black carbon mass and the coating thickness optically. The presence of a coating increased the black carbon particles’ ability to uptake water in a fashion dependent upon the precursor compound. The critical supersaturation of 200 nm mobility diameter black carbon particles was dramatically reduced by trace amounts of coatings. Evidence of apparent particle collapse upon coating was observed in particles with reduced mobility diameters and large coating thicknesses, as measured by the SP2.
