COMPARISON OF THE SCAQS TUNNEL STUDY WITH OTHER ON-ROAD VEHICLE EMISSION DATA

The Van Nuys Tunnel experiment conducted In 1987 by Ingalls et al. (see A&WMA Paper 89-137.3), to verify automotive emission inventories as part of the Southern California Air Quality Study (SCAQS), gave higher CO and HC emission-rate values than expected on the basis of automotive-emission models—by factors of approximately 3 and 4, respectively. The CO/NOx and HC/NOx emission-rate ratios moreover were higher than expected—by similar factors (NOx emission rates were about as expected). The purpose of the present paper is to review the literature on dynamometer and on-road (in tunnels and along roadways) testing of inuse vehicles, and on urban-air CO/HC/NOx concentration ratios, to see whether the Van Nuys Tunnel results are reasonable in terms of previous experience. The conclusions are that (1) on-road CO and HC emissions higher than expected have been reported before, (2) on-road CO and HC emissions consistent with the Van Nuys Tunnel results have been reported before, and (3) on-road CO/NOx and HC/NOx emission-rate ratios higher than expected have been reported before. The Van Nuys Tunnel NOx results actually are lower than in other on-road experiments, and the CO/NOx and HC/NOx ratios consequently are higher. The higher-than-predicted CO/NOx and HC/NOx ratios at Van Nuys and other on-road sites suggest richer operation on-road than predicted or than observed in the inuse-vehicle dynamometer tests which serve as the model inputs. Support for these suggestions and conclusions is found in comparison of urban-air and emission-inventory HC/NOx ratios. © 1990 Air & Waste Management Association.