Articles | Volume 18, issue 8
Atmos. Chem. Phys., 18, 5455–5466, 2018
Atmos. Chem. Phys., 18, 5455–5466, 2018

Research article 20 Apr 2018

Research article | 20 Apr 2018

Studying volatility from composition, dilution, and heating measurements of secondary organic aerosols formed during α-pinene ozonolysis

Kei Sato1, Yuji Fujitani1, Satoshi Inomata1, Yu Morino1, Kiyoshi Tanabe1, Sathiyamurthi Ramasamy1, Toshihide Hikida2, Akio Shimono2, Akinori Takami1, Akihiro Fushimi1, Yoshinori Kondo1, Takashi Imamura1, Hiroshi Tanimoto1, and Seiji Sugata1 Kei Sato et al.
  • 1National Institute for Environmental Studies, Ibaraki, 305-8506, Japan
  • 2Shoreline Science Research, Inc., Tokyo, 192-0045, Japan

Abstract. Traditional yield curve analysis shows that semi-volatile organic compounds are a major component of secondary organic aerosols (SOAs). We investigated the volatility distribution of SOAs from α-pinene ozonolysis using positive electrospray ionization mass analysis and dilution- and heat-induced evaporation measurements. Laboratory chamber experiments were conducted on α-pinene ozonolysis, in the presence and absence of OH scavengers. Among these, we identified not only semi-volatile products, but also less volatile highly oxygenated molecules (HOMs) and dimers. Ozonolysis products were further exposed to OH radicals to check the effects of photochemical aging. HOMs were also formed during OH-initiated photochemical aging. Most HOMs that formed from ozonolysis and photochemical aging had 10 or fewer carbons. SOA particle evaporation after instantaneous dilution was measured at  < 1 and  ∼ 40 % relative humidity. The volume fraction remaining of SOAs decreased with time and the equilibration timescale was determined to be 24–46 min for SOA evaporation. The experimental results of the equilibration timescale can be explained when the mass accommodation coefficient is assumed to be 0.1, suggesting that the existence of low-volatility materials in SOAs, kinetic inhibition, or some combined effect may affect the equilibration timescale measured in this study.

Short summary
The volatility distribution of α-pinene secondary organic aerosols (SOAs) was evaluated with a wide range of techniques, including offline chemical analysis and dilution- and heat-induced evaporation. Compounds less volatile than semi-volatile products, i.e., highly oxygenated molecules and dimers, were identified as products, and the SOA evaporation with equilibration timescales of 24–46 min after dilution were observed.
Final-revised paper