On-road emissions of carbonyls from light-duty and heavy-duty vehicles

Vehicle emissions are a major source of carbonyls, which play an important role in atmospheric chemistry and urban air quality. Yet, little data are a vailable for speciated carbonyls emitted by vehicles and especially by heav y-duty diesel vehicles. On-road vehicle emissions of carbonyls have been me asured in May 1999 at the Tuscarora Mountain Tunnel, PA. Ten saturated alip hatic aldehydes, 4 saturated aliphatic ketones, 4 unsaturated aliphatic car bonyls, 4 aliphatic dicarbonyls, and 9 aromatic carbonyls have been identif ied and their concentrations measured. For light-duty (LD) vehicles, total carbonyl emissions were ca. 6.4 mg/km, and the 10 largest emission factors were, in decreasing order, those of formaldehyde (2.58 +/- 1.85 mg/km, ca, 40% of total carbonyls), acetone, acetaldehyde, heptanal, crotonaldehyde, 2 -butanone, propanal, acrolein, methacrolein, and benzaldehyde. For weight c lass 7-8 heavy-duty diesel vehicles (7-8 HD), total carbonyl emissions were ca. 26.1 mg/km, and the 10 largest emission factors were, in decreasing or der, those of formaldehyde (6.73 +/- 2.05 mg/km, ca. 26% of total carbonyls ), acetaldehyde, acetone, crotonaldehyde, m-tolualdehyde, 2-pentanone, benz aldehyde, a Cg saturated aliphatic aldehyde isomer, 2,5-dimethylbenzaldehyd e, and 2-butanone. Aromatic carbonyls, unsaturated aliphatic carbonyls, 4 a liphatic dicarbonyls represented larger fractions of the total carbonyl emi ssions for 7-8 HD vehicles than for LD vehicles. For HD vehicles, formaldeh yde and acetaldehyde emission factors measured in this study are ca. 4-5 ti mes lower than those measured in previous work. For LD vehicles, emission f actors measured in this study are generally lower than those measured in ea rlier work and are about the same, within reported uncertainties, as those measured in 1992 in the same highway tunnel.