Heavy-duty trucks and buses are substantial contributors to the atmospheric oxides of nitrogen (NO{sub}x) inventory, but prediction of their emissions in real use remains inchoate. Continuous emissions of NO{sub}x were recorded from chassisdynamometer testing of eight vehicles using a variety of transient cycles, including the Central Business District schedule. NO{sub}x data were treated to account for sampling time lag and presented against instantaneous vehicle axle power. Data wererepeatable from run to run and test schedule, but vehicle type and test cycle both influenced the instantaneous emissions rates. However, the resulting correlations may be used for mobile source NO{sub}x contribution estimation when combined with vehicleactivity data. The emissions data were also presented as NO{sub}x,/CO{sub}2, which are valuable for comparison with remote sensing emissions data. The overall average ratio for all of the data considered was 0.0141, which corresponds to an emissionscontribution of 0.0423 g of NO{sub}x/g of diesel burned.
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