Photo‐oxidation of Isoprene with Organic Seed: Estimates of Aerosol Size Distributions Evolution and Formation Rates

Indoor smog chamber experiments have been conducted to investigate the dynamics of secondary organic aerosol (SOA) formation from OH‐initiated photo‐oxidation of isoprene in the presence of organic seed aerosol. The dependence of the size distributions of SOA on both the level of pre‐existing particles generated in situ from the photo‐oxidation of trace hydrocarbons of indoor atmosphere and the concentration of precursor, has been investigated. It was shown that in the presence of high‐level seed aerosol and low‐level isoprene (typical urban atmospheric conditions), particle growth due to condensation of secondary organic products on pre‐existing particles dominated; while in the presence of low‐level seed aerosol and comparatively high‐level isoprene (typical atmospheric conditions in rural region), bimodal structures appeared in the size distributions of SOA, which corresponded to new particle formation resulting from homogeneous nucleation and particle growth due to condensation of secondary organic products on the per‐existing particles respectively. The effects of concentrations of organic seed particles on SOA were also investigated. The particle size distributions evolutions as well as the corresponding formation rates of new particles in different conditions were also estimated.