Diurnal variation of semi-volatile dicarbonyls and hydroxycarbonyls in the urban atmosphere

Abstract

Diurnal variation of semi-volatile carbonyl compounds (glycolaldehyde, hydroxyacetone, glyoxal and methylglyoxal) were studied during July and August 2004 in urban Tokyo using an annular denuder sampling system and gas chromatography (GC). The carbonyls were collected on a deuder tube, whose surface was coated with O-Benzylhydroxylamine (BHA) and XAD-7 as collection reagent. The compounds were measured using a capillary GC after two-step derivatization processes with BHA and N, O-bis (trimethylsilyl) trifluoroacetamide (BSTFA). Gaseous concentration of semi-volatile carbonyl compounds showed a rapid increase in the morning and reached a maximum around noontime. Then, the concentrations significantly decreased in the evening and reached a minimum at midnight. The averaged concentrations were 1548 ng m^-3 for glycolaldehyde, 797 ng m^-3 for methylglyoxal, 406 ng m^-3 for glyoxal, and 362 ng m^-3 for hydroxyacetone. We found that these carbonyl concentrations were 2-21 times higher than those reported in the forest area in Japan. Good correlations were found among concentrations of the carbonyl compounds. Total concentrations of the compounds also showed a good correlation with oxidant (mostly ozone) and solar radiation, suggesting that secondary photochemical productions of carbonyl compounds are important.