Characterizing particulate matter emitted from on-road motor vehicles.

摘要

Recent epidemiological studies have found a correlation between mortality and ambient fine particulate matter (PM) levels. In urban areas, motor vehicles are a major source of fine and ultrafine PM. In order to aid in better understanding the contribution of the motor vehicle sector as a whole and to derive mass and number emission factors from individual classes of vehicles and the mechanisms contributing to them, the research presented in this dissertation was undertaken. A multi-lag linear regression approach was developed to calculate PM emission factors from on-road motor vehicles and two source attribution techniques were applied to apportion total PM emissions to specific mechanisms including tailpipe, resuspended road dust, tire-wear, and brake-wear. In order to characterize the size distribution of emitted particles and the particle number emission rates, a quantitative approach was also developed.; The findings of the source attribution component of the study revealed that the motor vehicles sector contributes 20% to 76% and 35% to 93% of the observed ambient PM₁₀ and PM_2.5 in seven urban areas, respectively. Using the multi-lag linear regression approach, on-road PM ₁₀ emission factors were determined and ranged from 530 to 9,100 mg/km and from 90 to 850 mg/km for HDD and LDSI vehicles, respectively. PM _2.5 emission factors ranged from 120 to 170 mg/km and from 10 to 90 mg/km for HDD and LDSI vehicles, respectively. The PM contributing to the above mass emission factors was found to be associated with resuspended road dust, tailpipe emissions, and brake-wear. No tire-wear was observed.; Vehicle particle size distributions were determined using an SMPS. Each measured size distribution consisted of two modes: a nucleation mode with midpoint diameter less than 20 nm and an accumulation mode with midpoint diameter less than 100 nm. The nucleation and accumulation components in some distributions exhibited second maxima, which may imply that such particle size distributions are superpositions of two particle size distributions: one attributed to the HDD vehicles and another attributed to either a different class of HDD vehicles or to LDSI vehicles. This decomposing technique enabled us to estimate particle production rates of 1.8 × 1013 and 2.8 × 10 14 particles per vehicle-km for LDSI and HDD vehicles, respectively.