PM Measurement Artifact: Organic Vapor Deposition on Different Filter Media

PM (Particulate Matter) emitted by vehicles and engines is most often measured quantitatively by collecting diluted exhaust samples on filters that are weighed pre-and post-test. The filter media used have high efficiency for small particles found in vehicle exhaust, but they also collect organic matter from the vapor phase with a lower, but nonzero, efficiency. In the past, organic vapor adsorption was usually negligible compared with PM levels from untreated diesel engine exhaust. For vehicles employing a DPF (Diesel Particulate Filter) and emitting very low PM, that is no longer the case. This paper reports measurements of the organic vapor deposition artifact for different filter media, including the two types (TX40 and Teflo) called for by the 2007 regulations for heavy duty diesel engines. The vapor artifact represents a substantial fraction of the 2007 regulatory standard of 10 mg/mi for light duty vehicles. It is 10 - 20% for Teflo and 30 - 50% for TX40 filters, implying that these filters will not provide equivalent measurements under the upcoming standard. The filter PM data are also compared to results based on thermometric analysis and electrical aerosol detection.