Formation of organic aerosols from the oxidation of biogenic hydrocarbons

Measurements of aerosol formation during the photooxidation of alpha-pinene, beta-pinene, d-3-carene, d-limonene, ocimene, linalool, terpinene-4-ol, and trans-caryophyllene were conducted in an outdoor smog chamber. Daylight experiments in the presence of NO, and dark experiments with elevated ozone concentrations were performed. The evolution of the aerosol was simulated by the application of a gas/particle absorption model in connection with a chemical reaction mechanism. The fractional aerosol yield is shown to be a function of the organic aerosol mass concentration and temperature. Ozone and, for selected hydrocarbons, the NO3 reaction of the compounds were found to represent efficient routes to the formation of condensable products, For initial hydrocarbon mixing ratios of about 100 ppb, the fractional aerosol yields from daylight runs have been estimated to be similar to 5% for open-chain hydrocarbons, such as ocimene and linalool, 5-25% for monounsaturated cyclic monoterpenes, such as alpha-pinene, d-3-carene, or terpinene-4-ol, and similar to 40% for a cyclic monoterpene with two double bonds like d-limonene. For the only sesquiterpene investigated, trans-caryophyllene, a fractional aerosol yield of close to 100% was observed. The majority of the compounds studied showed an even higher aerosol yield during dark experiments in the presence of ozone.