Characterization of on-road vehicle emissions and air quality in densely-built-environment

Vehicle emission is one major contributor of gaseous pollutants in the urban area. This work examines on-road gaseous emissions from different types of vehicles so that emission characteristics of vehicles under various operating conditions and vehicle emission's effect on air quality in a highly-developed city are better understood.;On-board and remote sensing measurements were carried out to examine emission from vehicles under urban driving conditions. On-board measurements show that emissions from one taxi are extraordinarily high when travelling at low speed, possibly due to malfunction of fuel supply control to the engine. Gaseous emissions from vehicles equipped with a catalytic converter are lower than those without one. Remote sensing measurements show that gaseous emissions of older LPG vehicles are higher compared to petrol and diesel vehicles of similar age, likely due to deterioration from the vehicles' extended use. Both on-board and remote sensing measurements show that emission factors and vehicle speed are inversely related while emission factors are higher when vehicles accelerate aggressively. Emission factors of taxis and light goods vehicles, derived from on-board and remote sensing measurements, are compared and their correlation is established to bridge the discrepancy between the two sets of emission factors. Emission factors are generally higher when measurements are collected on-board, due to dilution and reaction of vehicle emission in the atmosphere. Such comparison can improve measurement capabilities of remote sensing method.;Patterns in traffic volume and air quality in built-up areas within Hong Kong are examined to study vehicle emission's effect on urban air quality. This comparison reveals that urban air quality and traffic volume exhibit similar patterns, indicating that vehicle emissions strongly affect urban air quality. Statistical analysis shows that vehicle emissions strongly influence variations in NO2 concentration in the urban area but not PM 10. Such discrepancies indicate that variations in urban air quality depend largely on local sources. Discovery of long-memory property in urban air quality indicates that dispersion of vehicle emission is hindered by heavy development within the urban area. In addition, urban traffic conditions, under which vehicles emit more pollutants, can further deteriorate urban air quality.