Seasonal and diurnal variations of carbonyl compounds in Beijing ambient air

The levels of carbonyl compounds in Beijing ambient air were measured from November 2004 to October 2005. Formaldehyde, acetaldehyde and acetone were found to be the most abundant carbonyls. The concentrations of formaldehyde, acetaldehyde and acetone increased to 19.51±6.34, 17.18±4.57, 22.14±5.98 μg m−3, respectively, in summer from 5.14±2.56, 8.68±3.48, 9.18±3.27 μg m−3 in winter. Carbonyls showed excellent correlations with ozone in summer and significant correlations with CO in winter, which indicated that the sources of carbonyls were dominated by photo-oxidation of VOCs in summer and vehicular exhaust in winter. The photolysis rates of lower carbonyls calculated based on local zenith angle were one magnitude greater in summer than in winter. The distribution frequencies of carbonyls were analyzed from a database including 350 samples. The concentrations of the highest frequency were 9.0–19.0, 5.0–15.0 and 13.0–23.0 μg m−3 for formaldehyde, acetaldehyde and acetone, respectively.