Generation of Secondary Organic Aerosols in a Small Chamber for Toxicity Studies

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　To establish the air-liquid interface cell-exposure and inhalation toxicology studies of secondary organic aerosol (SOA), we developed a small reaction chamber system for generating SOA through α-pinene/ozone reaction (p-SOA), and photo-oxidation of m-xylene (x-SOA) and 1,3,5-trimethylbenzene (t-SOA) under presence of nitric oxide (NO). Size-resolved particle number concentrations (0.01-20 µm) and gaseous materials were monitored in the chamber. It is important to control the particle size and the concentration of residual ozone for air-liquid interface cell-exposure and inhalation studies and we found that the particle size of SOA via coagulation and condensation depends on initial concentration of precursor and ratio of precursor/NO. SOA was collected on Teflon filters to determine their physical and chemical properties and toxicity. The cytotoxicity of p-SOA and x-SOA was similar and was higher than that of t-SOA. On the other hand, oxidative stress induced by x-SOA was much higher than that induced by p-SOA and larger amount of oxidant in p-SOA was measured compared to that in x-SOA. Cytotoxicity and oxidative stress were different depending on the species of SOA, indicating that the amount of oxidant in SOA as well as the redox activity of SOA determine the cytotoxicity and oxidative stress of SOA.