An automated instrument for the quantitation of atmospheric carbonyls: Measurements and interpretation in southern Ontario.

摘要

An automated instrument for in-situ analysis of low molecular weight atmospheric carbonyl species has been developed. Adaptation of the DNPH silica cartridge method using an online derivatization and injection technique allowed coupling of an air sampling system to a micro-HPLC chromatographic system. Cycle times of 2 hours were obtained. Detection limits of 89 pptV, 54 pptV, 54 pptV and 39 pptV were obtained for formaldehyde, acetaldehyde, acetone, and glyoxal during field use. Detection limits for other carbonyls are estimated to be approximately 50 pptV. Experiments performed to determine the carbonyl collection efficiencies using the automated system confirmed complete recoveries of several carbonyl species.;Field measurements using a manually operated version of the technique were made as part of a field study in the summer of 1999 at an urban site in Hamilton Ontario. The technique successfully measured several important carbonyl species, showing reasonable results for many species of interest. Glyoxal concentrations during a tropospheric ozone episode, with winds from the southwest, were higher than what could be accounted for from known gas phase hydrocarbon chemistry, indicating the possibility of unknown sources.;In the summer of 2000 the automated instrument was used as part of a field study at an agricultural site in Simcoe, Ontario, located ∼70 km southwest of Hamilton. Glyoxal concentrations measured were again found to be significantly above what could be accounted for by known gas phase hydrocarbon oxidation chemistry. Possible mechanisms for the formation of glyoxal have been proposed. The contribution of formaldehyde, acetaldehyde and glyoxal to the daytime HO. radical source have been estimated to be 13.6%, 0.8% and 6.9% at midday, and somewhat enhanced during the early morning and late evening. Daytime formaldehyde sources from isoprene, methane, alkenes, acetaldehyde and alkanes are estimated as 42.5%, 23.9%, 21.6%, 11.3% and 0.6% respectively, assuming sources other than hydrocarbons and acetaldehyde to be insignificant. The alkene contribution was found to be dominated by HO . chemistry (∼87%), with a minor contribution from alkene reactions with ozone (∼13%). Acetaldehyde sources are estimated as 19%, 64%, and 17% for the alkanes, HO. with alkenes, and O3 with alkenes respectively. Alkenes represent a combined contribution of 81% of the total acetaldehyde production. Acetone was found to have a major source in i-butene and 2-methyl-2-butene despite their low levels of ˙˙∼20 pptV. Propane represents only ∼12% of the total acetone production and is therefore a relatively small source of acetone production at this site.