Carbon isotopic signatures of carbonyls from roadside air observation

Abstract

In this work, isotopic effects of carbonyls were evaluated during the simulation sampling of gaseous carbonyls by using a carbon isotope method developed, and then variation characteristics of carbon isotopic compositions were investigated for three dominant carbonyls including formaldehyde, acetaldehyde and acetone in the roadside air of Nanning for the first time. A small difference in δ¹³C values (0.04 to 0.50 ‰) were observed between the calculated and measured values of carbonyl-derivatives, indicating that the effect on carbon isotopic fractionation could hardly occurred in the simulation sampling of gaseous carbonyls. The roadside air measurements showed that \({\delta }^{13}\)C values of formaldehyde, acetaldehyde and acetone were –36.02 ‰ to –31.18 ‰, –35.35 ‰ to –32.01 ‰ and –30.45 ‰ to –29.09 ‰, respectively. Further correlation of the measured \({\delta }^{13}\)C values was good for formaldehyde, acetaldehyde and acetone (R² = 0.6275–0.7755), indicating that their similar sources could be the direct vehicular emission or indirect productions from precursors such as hydrocarbons. Particularly, formaldehyde, acetaldehyde and acetone in the roadside air were all enriched in the early afternoon by round 0.5–6 ‰ in ¹³C compared to other sampling durations, which was likely due to the contributions from the positive photo-oxidation productions of hydrocarbons. Finally, it was found that all measured \({\delta }^{13}\)C values (–36.5 ‰ to –29.0 ‰) agreed with the forecasted \({\delta }^{13}\)C range (–43.0 ‰ to –26.0 ‰) according to the ¹³C mass balance of carbonyls and their precursors such as hydrocarbons, indirectly confirming such positive productions in the roadside air.