Vehicle emissions and roadside air quality
Muncaster, Gary M.
Individual carbon monoxide and hydrocarbon emissions were monitored from passing vehicles using the Fuel Efficiency Automobile Test at four survey sites (Bounds Green Road, \ud Haringey (site A); Dixons Bank, Middlesborough (site B); Abbey Street, Southwark (site C); Uppingham Road, Leicester (site D)}. The remotely measured emissions data is described \ud in terms of fleet emissions, model year emissions and model year contribution to fleet emissions. It was found that there were a large majority of low emitting vehicles contributing little to fleet emissions and a small minority of high emitting vehicles contributing significant proportions to fleet emissions. Model year analysis suggested a low association between \ud vehicle age and mean emissions prior to 1983 but a much improved relationship after 1983. Analysis of model year contributions to fleet emissions shows new gross polluters to be the largest contributors and older vehicles playing only a minor role.\ud The concentrations of carbon monoxide and nitrogen oxides in air were monitored, in conjunction with the FEAT measurement, at various distances from the road (roadside (on the kerb), kerbside (3 metres from the road), 7.5 metres and 15 metres from the road). A decrease of carbon monoxide and nitric oxide concentrations with distance from the road was noted for all sites with the exception of site D where meteorological parameters exerted a greater influence upon air quality than did distance from the road. The expected increase of NO2 concentration with distance from the road, as NO is oxidised to NO2, did not occur. Moreover, NO2 concentrations decreased with distance from the road. However, the production of NO2 by oxidation of NO can be inferred in two ways. Firstly, a much more gradual decline in concentrations with distance from the road was noted for NO2 compared to CO and NO, possibly due to NO2 production counteracting the reduction in concentration caused by dispersion. Secondly, an analysis of the change of ratios between nitrogen dioxide and nitric oxide with distance from the road reveals a relative increase of NO2 with distance.\ud The air quality data were compared with the remotely measured vehicle emissions data, wind speed and wind direction. A statistical examination of the data was undertaken on a halfhourly and five minute basis (no wind data was available on a five minute basis). The halfhourly analyses for both CO and NOx produced positive correlations between vehicle emissions data and air quality, and predominantly negative correlations between wind speed and air quality. Both positive and negative correlations were observed between wind direction and CO/NOx air quality . Regression analyses were undertaken where the results were statistically significant at a 0.1 level. This reduced the sample size for CO to data collected on eight individual sampling days and to only two days for NOx• All the analysed CO sampling days recorded r2 values of greater than 0.5, such that for each sampling day at least half the variation in CO air quality is explained by the variation in on-road vehicle emissions, wind speed and wind direction. The two analysed NOx sampling days recorded r values of approximately 0.8. The five minute analyses produced were less statistically significant giving only a low degree of correlation between CO and NOx air quality and on-road vehicle emissions. Regression analyses were undertaken for only two days for CO and only one day for NOx.
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