13C isotope evidence for photochemical production of atmospheric formaldehyde, acetaldehyde, and acetone pollutants in Guangzhou

Ambient formaldehyde, acetaldehyde, and acetone are harmful air pollutants with potential carcinogenic effects on human health. They are considered as important photochemical products from photo-oxidation of atmospheric hydrocarbons. However, little is known on the effet of photodegradation of air pollutants on delta C-13 values. Here, we report the first C-13 isotope evidence for the photochemical production of ambient formaldehyde, acetaldehyde, and acetone. Air samples were collected each day during early morning, noon, early afternoon, and late afternoon on 17-19 September 2008 in Guangzhou by drawing air through 2,4-dinitrophenylhydrazine-coated cartridges. The samples were analyzed using high-performance liquid chromatography for concentration analysis and then using gas chromatography-combustion-isotope ratio mass spectrometry for delta C-13 analysis. Our results show that ambient formaldehyde, acetaldehyde, and acetone were enriched by 1-5 aEuro degrees in C-13 in the early afternoon relative to other sampling durations, and they also exhibited the highest concentrations in the early afternoon. Measured delta C-13 values of formaldehyde, acetaldehyde, and acetone were in the range from -37.15 to -29.01 aEuro degrees. The observed enrichment in C-13 implied important photochemical production together with the highest concentrations in the early afternoon. Especially, measured delta C-13 range from -37.15 to -29.01 aEuro degrees was in accordance with forecasted delta C-13 range from -43 to -28 aEuro degrees based on the mass balance in C-13 between the carbonyls and its major hydrocarbon precursors, providing important C-13 isotope evidence for the photochemical production of ambient formaldehyde, acetaldehyde, and acetone.