Gas/particle partitioning of carbonyls in the photooxidation of isoprene and 1,3,5-trimethylbenzene

A new denuder-filter sampling technique has been used to investigate the gas/particle partitioning behaviour of the carbonyl products from the photooxidation of isoprene and 1,3,5-trimethylbenzene. A series of experiments was performed in two atmospheric simulation chambers at atmo- spheric pressure and ambient temperature in the presence of NOx and at a relative humidity of approximately 50%. The denuder and filter were both coated with the derivatizing agent O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PF- BHA) to enable the efficient collection of gas- and particle- phase carbonyls respectively. The tubes and filters were ex- tracted and carbonyls identified as their oxime derivatives by GC-MS. The carbonyl products identified in the experiments accounted for around 5% and 10% of the mass of secondary organic aerosol formed from the photooxidation of isoprene and 1,3,5-trimethylbenzene respectively. Experimental gas/particle partitioning coefficients were determined for a wide range of carbonyl products formed from the photooxidation of isoprene and 1,3,5- trimethylbenzene and compared with the theoretical values based on standard absorptive partitioning theory. Photooxi- dation products with a single carbonyl moiety were not ob- served in the particle phase, but dicarbonyls, and in particu- lar, glyoxal and methylglyoxal, exhibited gas/particle parti- tioning coefficients several orders of magnitude higher than expected theoretically. These findings support the impor- tance of heterogeneous and particle-phase chemical reactions for SOA formation and growth during the atmospheric degra- dation of anthropogenic and biogenic hydrocarbons.