Climate-relevant properties of diesel particulate emissions: results from a piggyback study in Bangkok, Thailand.

A "piggyback" approach is used to characterize aerosol emissions to obtain input for large-scale models of atmospheric transport. Particulate and gaseous emissions from diesel trucks, light-duty vehicles, and buses were measured by the Bangkok Pollution Control Department as part of the Developing Integrated Emissions Strategies for Existing Land Transport (DIESEL) project. We added filter-based measurements of carbonaceous composition, particulate light absorption, and water uptake. For 88 "normal" diesel vehicles (PM emission rate < 4.7 g/kg), our best estimate of the average PM2.5 emission rate is 2.2 +/- 0.5 g/kg, whereas for 15 high emitters, it is 8.4 +/- 1.9 g/kg. The effect of Euro standards on PM emission rates was apparent for heavy-duty vehicles, but not for light-duty vehicles. Carbonaceous composition appears relatively consistent, with particulate (artifact-corrected) OC at 17 +/- 1% and EC at 40 +/- 8% of PM for 103 pickups, vans, heavy-duty trucks and buses. The median absorption cross-section for EC is 10.5 m2/g at 532 nm. The history of average emission rate and chemical composition during the project suggests that about 25 vehicles can provide a regional PM emission rate for normal vehicles. Other studies such as remote sensing measurements will be required to estimate the important contribution of high-emitting vehicles.