AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Secondary Organic Aerosol Formation from the Isoprene Ozonolysis: Effect of OH Radical Scavenger on the Radical Chemistry
KEI SATO, Satoshi Inomata, Risa Uchida, Takashi Imamura, Jun Hirokawa, Motonori Okumura, Susumu Tohno, National Institute for Environmental Studies
Abstract Number: 76 Working Group: Aerosol Chemistry
Abstract In laboratory experiments of ozone-alkene reactions, radical scavengers are used to suppress reactions with OH radicals produced. The secondary organic aerosol (SOA) yields from the ozone-cyloalkene reactions are known to be dependent on the scavenger compound. In this study, we conducted ozone-isoprene reaction experiments using (1) no scavenger, (2) cyclohexane as the scavenger, or (3) carbon monoxide as the scavenger. A 6-m3 evacuable chamber was used. The concentrations of ozone and isoprene were monitored by FT-IR. The size-distribution of SOA was monitored by SMPS. The SOA yields of experiments 1, 2, and 3 were determined to be 1.2%, 1.3% and 0.3%, respectively. The rate constant determined for the ozone-isoprene reaction from reactant time profile data of experiments 2 and 3 agreed with the literature values. The fraction of 2-methyltetrols to total SOA mass measured by derivatization-GC/MS analysis in experiment 1 was much higher than those measured in experiments 2 and 3. These results suggest that the OH + isoprene reaction is successfully suppressed in the experiments conducted using the scavenger. Only in the SOA offline sample obtained in experiment 2, adipic acid and C6 hydroxycarboxylic acid were detected. On the other hand, ozone/propylene/cyclohexane system experiment was conducted to study SOA formation from the OH + cyclohexane reaction; however, the concentration of SOA produced was very low; and the C6 products were not detected in the offline sample. The C6 products detected in experiment 2 will be produced as a result of coexistence of RO2 radicals from the OH + cylcohexane reaction and products from the ozone-isoprene reaction. The SOA yield measured using CO represents a value which is not affected by reactions with RO2 radicals originated from radical scavengers. The SOA yield measured in this study using CO was about one third of those measured in the previous study using n-hexane.