Effect of experimental conditions on secondary organic aerosol formation in an oxidation flow reactor

As global air pollution aggravates, it urges us to investigate the evolution of atmospheric related emissions. Recently oxidation flow reactor (OFR) has been widely used to simulate the aging of atmospheric related emissions as its excellent performance. In this work, we systematically characterized the SOA formation from a-pinene using a custom-built OFR under different conditions. The particle loss of the OFR was evaluated by particle transmission efficiency, then the effect of O-3 concentration, relative humidity (RH), precursor amounts, OH exposure level, and acidic seed aerosol on SOA formation was investigated. The particle losses of our OFR for particles above 50 nm were very small, which was comparable to or even better than those of previous traditional flow reactors. The formation of SOA particles nearly achieved stability after UV radiation for 15 min. When OH exposure concentration at approximately 0.6 x 10(12) molec cm(-3) s, the SOA yield reached the maximum yield of 0.51 and 0.39 in the presence and absence of acidic seed aerosol respectively. The addition of acidic seed aerosol increased both particle number concentration and particle size, resulting in an increase of SOA yield of 1.2-1.5 times at OH exposure concentration ranged from 0.1 x 10(12) to 1.8 x 10(12) molec cm(-3) s. The results provided significant guidance for studying the aging of atmospheric related emission under different working conditions by using an OFR.