Carboxylic acids in secondary aerosols from oxidation of cyclic monoterpenes by ozone

A series of smog chamber experiments have been conducted in which five cycl ic monoterpenes were oxidized by ozone. The evolved secondary aerosol was a nalyzed by GC-MS and HPLC-MS for nonvolatile polar oxidation products with emphasis on the identification of carboxylic acids. Three classes of compou nds were determined at concentration levels corresponding to low percentage molar yields: i.e. dicarboxylic acids, oxocarboxylic acids, and hydroxyket ocarboxylic acids. Carboxylic acids are highly polar and have lower vapor p ressures than their corresponding aldehydes and may thus play an important role in secondary organic aerosol formation processes. The most abundant ca rboxylic acids were the following: cis-pinic acid AB1 (cis-3-carboxy-2,2-di methylcyclobutylethanoic acid) from alpha- and beta-pinene; cis-pinonic aci d A3 (cis-3-acetyl-2,2-dimethylcyclobutylethanoic acid) and cis-10-hydroxyp inonic acid AB6 (cis-2,2-dimethyl-3-hydroxyacetylcyclobutylethanoic acid) f rom alpha-pinene and beta-pinene; cis-3-caric acid C1 (cis-2,2-dimethyl-1,3 -cyclopropyldiethanoic acid), cis-3-caronic acid C3 (2,2-dimethyl-3-(2-oxop ropyl)cyclopropanylethanoic acid), and cis-10-hydroxy-3-caronic acid C6 (ci s-2,2-dimethyl-3-(hydroxy-2-oxopropyl)cyclopropanylethanoic acid) from 3-ca rene; cis-sabinic acid S1 (cis-2-carboxy-1-isopropylcyclopropylethanoic aci d)from sabinene; limonic acid L1 (3-isopropenylhexanedioic acid), limononic acid L3 (3-isopropenyl-6-oxo-heptanoic acid), 7-hydroxylimononic acid L6 ( 3-isopropenyl-7-hydroxy-6-oxoheptanoic acid), and 7-hydroxylimononic acid L 6' (7-hydroxy-3-isopropenyl-6-oxoheptanoic acid) from limonene.