On-road measurement of carbonyls in California light-duty vehicle emissions

Emissions of carbonyls by motor vehicles are of concern because these speci es can be hazardous to human health and highly reactive in the atmosphere. The objective of this research was to measure carbonyl emission factors for California light-duty motor vehicles. Measurements were made at the entran ce and exit of a San Francisco Bay area highway tunnel, in the center bore where heavy-duty trucks are not allowed. During summer 1999, approximately 100 carbonyls were identified, including saturated aliphatic aldehydes and ketones, unsaturated aliphatic carbonyls, aliphatic dicarbonyls, and aromat ic carbonyls. Concentrations were measured for 32 carbonyls and were combin ed with NMOC, CO, and CO2 concentrations to calculate by carbon balance emi ssion factors per unit of fuel burned. The measured carbonyl mass emitted f rom light-duty vehicles was 68 +/- 4 mg L-1. Formaldehyde accounted for 45% of the measured mass emissions, acetaldehyde 12%, tolualdehydes 10%, benza ldehyde 7.2%, and acetone 5.9%. The ozone forming potential of the carbonyl emissions was dominated by formaldehyde (70%) and acetaldehyde (14%). Betw een 1994 and 1999, emission factors measured at the same tunnel for formald ehyde, acetaldehyde, and benzaldehyde decreased by 45-70%. Carbonyls consti tuted 3.9% of total NMOC mass emissions and 5.2% of NMOC reactivity. A comp arison of carbonyl emissions with gasoline composition supports previous fi ndings that aroma ic aldehyde emissions are related to aromatics in gasolin e. Carbonyl concentrations in liquid gasoline were also measured. Acetone a nd MEK were the most abundant carbonyls in unburned gasoline; eight other c arbonyls were detected and quantified.