Biogenic Secondary Organic Aerosol: Observations and Predictions

QI CHEN (1), Yingjun Liu (1), Yongjie Li (2), Scot T. Martin (1)

(1) School of Engineering and Applied Sciences & Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA (2) Environmental Engineering Program, Hong Kong University of Science and Technology, Hong Kong, China

     Abstract Number: 577
     Last modified: May 13, 2010

Abstract
Laboratory studies using simulation chambers contribute greatly to our knowledge about biogenic secondary organic aerosol (SOA) formation. However, information on the particle-phase composition, especially at low organic loadings where only the least volatile oxidation products can effectively partition to the particle phase, are still limited. SOA formation from sesquiterpenes remains far from fully characterized because of not only the discrepancy between the experimental and real atmospheric conditions but also the complex nature of multi-generation oxidation of sesquiterpenes. In the present study, SOA formation from the dark ozonolysis of sesquiterpene beta-caryophyllene is investigated at low organic loadings (i.e., 0.1 to 30 µg m$^(-3)). Unlike most of the previous laboratory studies of beta-caryophyllene ozonolysis that were carried under ozone-limited conditions, we conducted the experiments under conditions of excess ozone, which are similar with atmosphere conditions and can facilitate the formation of second-generation oxidation products. The chemical composition of the sesquiterpene SOA particles is characterized by using both on-line aerosol mass spectrometry and off-line liquid chromatography. Moreover, for the three representative biogenic SOA systems studied in the Harvard Environmental Chamber at atmospherically relevant organic loadings including isoprene (C$_5) photooxidation, alpha-pinene (C$_(10)) ozonolysis, and beta-caryophyllene (C$_(15)) ozonolysis, the particle yield, mass spectra and element composition of SOA particles are compared. The particle-phase products are predicted by coupling the Master Chemical Mechanism (MCM) with volatility-driven partitioning. By matching the elemental composition of predicted as well as observed particle-phase products with that of the bulk SOA particles, the role of particle-phase SOA pathways is investigated.