AEROSOL FORMATION AND GROWTH IN ATMOSPHERIC ORGANIC NOX SYSTEMS .1. OUTDOOR SMOG CHAMBER STUDIES OF C-7-HYDROCARBONS AND C-8-HYDROCARBONS

Outdoor smog chamber experiments have been performed to determine the aerosol-forming potential of selected C-7- and C-8-hydrocarbons in sunlight-irradiated hydrocarbon-NOx mixtures. Measured aerosol size distributions were used to determine the rates of gas-to-particle conversion and to study the effects of the addition of SO2 and/or NH3 on aerosol formation and growth. The average aerosol yields by mass for the hydrocarbons studied were (the range of measured values for methylcyclohexane and 1-octene are in parentheses): methylcyclohexane 9.2% (0.12-18.8); 1-octene 4.2% (0.17-6.9); toluene 18.6%; n-octane < 0.001%. The average yields are accompanied by large standard deviations (see Table 3) and depended strongly on the conditions, particularly the hydrocarbon to NOx initial concentration ratio. Addition of SO2 to the organic/NOx systems led to an early nucleation burst and subsequent rapid growth of the newly formed aerosol. In the presence of NH3, the gas-to-particle conversion rate of the organic/NOx system was enhanced perhaps due to the formation of NH4NO3 or the reaction of NH3 with carboxylic acids. Sustained particle formation was observed when both SO2 and NH3 were present, presumably as a result of (NH4)2SO4 formation. We have estimated the complexity of the 1-octene aerosol and identified 5-propyl furanone as a component of the aerosol.