Atmospheric simulation chamber studies of secondary organic aerosol formation from photooxidation of naphthalene under various conditions

Laboratory studies of secondary organic aerosol (SOA) formation from the photooxidation of VOCs have mainly focused on determination of the aerosol yield under a variety of reaction conditions. The aerosol yields show a strong dependence on temperature, hydrocarbon to NO_x ratios and the OH concentration during the photooxidation process. The SOA yield arising from naphthalene photooxidation under different reaction conditions was investigated. A series of simulation chamber experiments were performed using NO_x and HONO as the OH precursor in the absence of seed aerosol. By varying the initial NO_x and naphthalene concentrations, it was shown that reactions with a higher hydrocarbon to NO_x ratio generated particles more quickly and produced higher SOA yields. SOA yield also increased by up to a factor of 1.5 over the relative humidity range 0-50%. Water may promote SOA formation and growth by conversion of photooxidation products into less volatile compounds via reaction in the gas or particle phase. The results indicated that naphthalene was a potentially large source of SOA in urban areas and should be included in atmospheric SOA models. However, as chamber experiments are not truly representative of the real atmosphere, extrapolation of the results from the present work should be treated with caution. The study also highlighted the need for further detailed investigations of SOA formation from naphthalene and other PAHs under various reaction conditions. This is an abstract of a paper presented at the 106th AWMA Annual Conference and Exhibition (Chicago, IL 6/25-28/2013).