Ozone-initiated reactions with mixtures of volatile organic compounds under simulated indoor conditions

This study examines the primary and secondary products resulting from reactions initiated by adding ozone to complex mixtures of volatile organic compounds (VOC). The mixtures were representative of organic species typically found indoors, but the concentrations tended to be higher than normal indoor levels. Each 4-h experiment was conducted in a controlled environmental facility (CEF, 25 m(3)) ventilated at similar to1.8 h(-1). The mixture investigated included 23 VOC (no O-3), O-3/23 VOC, O-3/21 VOC (no d-limonene or a-pinene), and O-3/terpene only (d-limonene and a-pinene). The net O-3 concentration was similar to40 ppb in each experiment, and the total organic concentration was 26 mg/m(3) for the 23 VOC mixture, 25 mg/m(3) for the 21 VOC mixture, and 1.7 mg/m(3) forthe d-limonene and alpha-pinene mixture. When the 23 VOC were added to the CEF containing no O-3, no compounds other than those deliberately introduced were observed. When O-3 was added to the CEF containing the 23 VOC mixture, both gas and condensed phase products were found, including aldehydes, organic acids, and submicron particles (140 mug/m(3)). When O-3 was added to the CEF containing the 21 VOC without the two terpenes (O-3/21 VOC condition), most of the products that were observed in the 03/23 VOC experiments were no longer present or present at much lower concentrations. Furthermore, the particle mass concentration was 2-7 mug/ m3, indistinguishable from the background particle concentration level. When O-3 was added to the CEF containing only two terpenes, the results were similar to those in the O-3/23 VOC experiments, but the particle mass concentration (190 mug/m(3)) was higher. The results indicate that (i) O-3 reacts with unsaturated alkenes under indoor conditions to generate submicron particles and other potentially irritating species, such as aldehydes and organic acids; (ii) the major chemical transformations that occurred under our experimental conditions were driven by O-3/d-limonene and Ova-pinene reactions; and (iii) the hydroxyl radicals (OH) that were generated from the O-3/terpene reactions played an important role in the chemical transformations and were responsible for approximately 56-70% of the formaldehyde, almost all of the p-tolualdehyde, and 19-29% of the particle mass generated in these experiments.