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Development of Particulate Matter Mass Measurement Methods for Atmospheric Air Quality Monitoring and Very Low Vehicle Emissions


The public raises concerns about the exposure to particulate matter (PM) which has been strongly associated with illness and mortality. However, most of the studies relied on the measurements from stationary monitoring sites, which cannot capture the actual PM exposure for those at or near the source. In this study, both stationary and comprehensive mobile monitoring platforms were developed to measure PM concentration and traffic conditions on some major highways in Southern California. The main objective is to develop a set of alternative metrics that measure particle concentrations as well as particle size. Measurement of particle size distributions are useful but doing so to monitor a wide region is not practical. The use of a particle counter and a diffusion charger was investigated as a relatively simple means to measure spatiotemporally-resolved particle concentrations over a wide region using a mobile platform. While the condensation particle counter and electrical aerosol detector respectively measure particle number and particle active surface area concentrations, the ratio of surface area over number provides an additional information of particle size which is important for particle transport. Particle size distributions measured by scanning mobility particle sizer during ambient monitoring were used to verify the concept. The study found that alternative metrics (number, surface area, and ratio of surface area over number) can be used to monitor spatiotemporally resolved particle concentrations over a wide region.

Gravimetric sampling methods on a chassis dynamometer were studied in accordance to Code of Federal Regulations. This study evaluated commercially available partial flow dilutors with a focus on their equivalency with the standard constant volume sampler system and the ability to provide reproducible measurements at low PM emission levels. As PM standards for light-duty vehicles are becoming more stringent, improving the confidence and understanding the mass measurement methods become one of the main goals for the industry and regulatory agencies. Simultaneous testing was conducted with three partial flow dilutors over the Federal Test Procedure and US06 drive cycles. The Federal Test Procedure had means that were statistically different for two of the three partial flow dilutors. As for the US06 tests, the mean differences were not statistically different. The performance of all partial flow dilutors also showed repeatable and accurate level of proportionality, which could easily meet the Code of Federal Regulations 1066 and 1065 requirements for all tests performed.

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