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 δ¹³C values. Here, we report the first ¹³C 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 δ¹³C analysis. Our results show that ambient formaldehyde, acetaldehyde, and acetone were enriched by 1–5 ‰ in ¹³C in the early afternoon relative to other sampling durations, and they also exhibited the highest concentrations in the early afternoon. Measured δ¹³C values of formaldehyde, acetaldehyde, and acetone were in the range from ?37.15 to ?29.01 ‰. The observed enrichment in ¹³C implied important photochemical production together with the highest concentrations in the early afternoon. Especially, measured δ¹³C range from ?37.15 to ?29.01 ‰ was in accordance with forecasted δ¹³C range from ?43 to ?28 ‰ based on the mass balance in ¹³C between the carbonyls and its major hydrocarbon precursors, providing important ¹³C isotope evidence for the photochemical production of ambient formaldehyde, acetaldehyde, and acetone.