Real-world emission factors of fifteen carbonyl compounds measured in a Hong Kong tunnel

Real-world vehicle emissions of carbonyls were determined in summer and winter of 2003 at the Shing Mun Tunnel, Hong Kong. Fifteen carbonyl species have been analyzed in this study. The total measured carbonyls emission factors ranged from 21.7 to 68.9 mg veh^-1 km^-1 among different measurement periods, with an average of 35.8±11.9 mg veh^-1 km^-1. Higher carbonyl emissions were found to be associated with a high proportion of diesel-fueled vehicles. Total measured carbonyl emissions from Diesel-fueled Vehicle (DV, 71.5 mg veh^-1 km^-1) were about 7 times higher than those from Non-Diesel-fueled Vehicle (NDV, 10 mg veh^-1 km^-1). The five carbonyls with the largest DV emission factor were, in decreasing order, formaldehyde (38.3 mg veh^-1 km^-1), acetaldehyde (11.4 mg veh^-1 km^-1), acetone (5.3 mg veh^-1 km^-1), crotonaldehyde (5.2 mg veh^-1 km^-1) and benzaldehyde (2.0 mg veh^-1 km^-1). These five carbonyl compounds together accounted for 87% of the sum of all DV carbonyl emission factors. For NDV, the five most abundant carbonyls in NDV emission at the tunnel were, in decreasing order, formaldehyde (3.5 mg veh^-1 km^-1), acetone (1.8 mg veh^-1 km^-1), methyl ethyl ketone (1.6 mg veh^-1 km^-1), m,p-tolualdehyde (1.0 mg veh^-1 km^-1) and acetaldehyde (mg veh^-1 km^-1). They accounted for 85% of the sum of all NDV carbonyl emission factors.