No abstract

No abstract

background location and were highest (29 ppb) at the Azusa, CA, monitoring site that is downwind of downtown Los Angeles. Formaldehyde (urban average 5.3 ppb), acetaldehyde, and acetone accounted for 24%, 18%, and 7%, respectively, of the total carbonyls on a ppbv basis. The nine high MW carbonyls (C 8 -C 14 ) accounted for 11-14% of the total carbonyls. The acetaldehyde/formaldehyde concentration ratio averaged 0.75 at the urban locations. Ranking of the measured carbonyls with respect to removal of the hydroxyl radical showed acetaldehyde to be the most important followed by formaldehyde and nonanal. Diurnal and spatial variations in ambient carbonyls levels are briefly examined and appear to be consistent with both direct emissions and insitu formation during eastward transport over the urban area.

No abstract

The gas-phase reaction of ozone with C5 -Clo alkenes (eight 1-alkenes, four 1,l-disubstituted alkenes, and cyclohexene) has been investigated a t atmospheric pressure and ambient temperature (285-293 K). Cyclohexane was added to scavenge the hydroxyl radical, which forms as a product of the ozonealkene reaction. The reaction rate constants, in units of cm3 molecule-' s-l, are 9.6 ? 1.6 for 1-pentene, 9.7 ? 1.4 for 1-hexene, 9.4 5 0.4 for 1-heptene, 12.5 ? 0.4 for 1-octene, 8.0 ? 1.4 for 1-decene, 3.8 ? 0.6 for 3-methyl-l-pentene, 7.3 -+ 0.7 for 4-methyl-l-pentene, 3.9 5 0.9 for 3,3-dimethyl-1-butene, 13.3 -f 1.4 for 2-methyl-l-butene, 12.5 5 1.1 for 2-methyl-1-pentene, 10.0 5 0.3 for 2,3-dimethyl-l-butene, 13.7 2 0.9 for 2-ethyl-1-butene, and 84.6 ? 1.0 for cyclohexene. Substituent effects on alkene reactivity are examined. Steric effects appear to be important for all 1,l-disubstituted alkenes as well as for those 1-alkenes that bear s-butyl and t-butyl groups. The results are briefly discussed with respect to the atmospheric persistence of the alkenes studied. @I

Carbonyls can be toxic and highly reactive in the atmosphere. To quantify trends in carbonyl emissions from light-duty (LD) vehicles, measurements were made in a San Francisco Bay area highwaytunnel bore containing essentially all LD vehicles during the summers of 1999, 2001, and 2006. The LD vehicle emission factor for formaldehyde, the most abundant carbonyl, did not change between 1999 and 2001, then decreased by 61 +/- 7% between 2001 and 2006. This reduction was due to fleet turnover and the removal of MTBE from gasoline. Acetaldehyde emissions decreased by 19 +/- 2% between 1999 and 2001 and by the same amount between 2001 and 2006. Absent the increased use of ethanol in gasoline after 2003, acetaldehyde emissions would have further decreased by 2006. Carbonyl emission factors for medium- (MD) and heavy-duty (HD) diesel trucks were measured in 2006 in a separate mixed-traffic bore of the tunnel. Emission factors for diesel trucks were higher than those for LD vehicles for all reported carbonyls. Diesel engine exhaust dominates over gasoline engines as a direct source of carbonyl emissions in California. Carbonyl concentrations were also measured in liquid-gasoline samples and were found to be low (< 20 ppm). The gasoline brands that contained ethanol showed higher concentrations of acetaldehyde in unburned fuel versus gasoline that was formulated without ethanol. Measurements of NO2 showed a yearly rate of decrease for LD vehicle emissions similar to that of total NOx in this study. The observed NO2/NOx ratio was 1.2 +/- 0.3% and 3.7 +/- 0.3% for LD vehicles and diesel trucks, respectively.

No abstract

Vehicle emissions are a major source of carbonyls, which play an important role in atmospheric chemistry and urban air quality. Yet, little data are available for speciated carbonyls emitted by vehicles and especially by heavy-duty diesel vehicles. On-road vehicle emissions of carbonyls have been measured in May 1999 at the Tuscarora Mountain Tunnel, PA. Ten saturated aliphatic aldehydes, 4 saturated aliphatic ketones, 4 unsaturated aliphatic carbonyls, 4 aliphatic dicarbonyls, and 9 aromatic carbonyls have been identified 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 +/- 1.05 mg/km, ca. 40% of total carbonyls), acetone, acetaldehyde, heptanal, crotonaldehyde, 2-butanone, propanal, acrolein, methacrolein, and benzaldehyde. For weight class 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 order, those of formaldehyde (6.73 +/- 2.05 mg/km, ca. 26% of total carbonyls), acetaldehyde, acetone, crotonaldehyde, m-tolualdehyde, 2-pentanone, benzaldehyde, a C5 saturated aliphatic aldehyde isomer, 2,5-dimethylbenzaldehyde, and 2-butanone. Aromatic carbonyls, unsaturated aliphatic aldehydes, and aliphatic dicarbonyls represented larger fractions of the total carbonyl emissions for 7-8 HD vehicles than for LD vehicles. For HD vehicles, formaldehyde and acetaldehyde emission factors measured in this study are ca. 4-5 times lower than those measured in previous work. For LD vehicles, emission factors measured in this study are generally lower than those measured in earlier work and are about the same, within reported uncertainties, as those measured in 1992 in the same highway tunnel.