Study of the PM Gas-Phase Filter Artifact Using a Setup for Mixing Diesel-Like Soot and Hydrocarbons

Abstract

The filter artifact is a significant source of error in gravimetric measurements of particulate matter (PM) exhaust. However, only a few studies on the subject exist. Results from these studies show a large discrepancy mainly because the experiments were performed using real diesel vehicle exhaust with varying exhaust composition. In this study, a setup for mixing diesel-like soot and hydrocarbon vapor was constructed for generating a stable exhaust aerosol with adjustable composition. The particle size distribution of the diesel-fueled soot generator (GMD [geometric mean diameter] adjustable between 27 and 164 nm) was found to represent "real" exhaust particulate emission. This setup was applied for studying the filter artifact on Teflon-coated glass fiber filters using pentadecane as the hydrocarbon vapor. Experiments were performed using particle and hydrocarbon concentrations of 130-700 µg/m 3 and 10-12 ppm, respectively. It was found that the particle concentration of the aerosol affects the filter artifact. At lower particle concentrations, more hydrocarbon adsorption was detected. In the absence of particles, the adsorption was highest. Furthermore, filter soot load, corresponding to 0.13%-0.66% of the clean filter mass, was found to affect adsorption. Sooty filters adsorbed less vapor than clean filters. However, increasing the soot load resulted in more adsorption. Moreover, it was found that the backup filter serves as a reasonable estimate of the filter artifact only for low particle concentrations and filter soot loads. These results indicate that the filter soot load is an important parameter influencing the filter artifact, and therefore, it should be considered when performing gravimetric sampling. The setup was proven to be a unique tool for quantitative studies of the filter artifact.

Time-resolved characterization of primary particle emissions and secondary particle formation from a modern gasoline passenger car

“…Collection efficiency (CE) value represents the fraction of sampled particle mass that is detected by the detector and CE value is needed for the calculation of aerosol mass concentration measured by the AMS. Previous studies have shown that the CE of SP-AMS is affected by (i) particle losses during transit through the inlet and lens, (ii) the particle beam divergence for both tungsten and laser vaporizers and for tungsten vaporizer also due to (iii) bounce effects from the vaporizer (Huffman et al, 2009;Matthew et al, 2008;Onasch et al, 2012). It is known that in the standard AMS with only the tungsten vaporizer the CE can depend on the chemical composition and acidity of aerosol as well as sampling relative humidity (Middlebrook et al, 2012), the default value for the CE being 0.5.…”

“…This technology development also has, in general, other effects than required by emission legislation; for example, fuel sulfur content limitations affect the emissions of nanoparticles. It should be noted that, e.g., semi-volatile compounds (e.g., low-volatility organics, sulfuric compounds) are not directly regulated even though they are partially detected in the gravimetric PM determination as P. Karjalainen et al: Time-resolved secondary particle formation from a gasoline car particles or adsorbed gas phase artefacts (Chase et al, 2004;Högström et al, 2012). Although not directly regulated, lowvolatility organics are likely to be affected by gaseous hydrocarbon limits.…”

Investigation of alternative metrics to quantify PM mass emissions from light duty vehicles

“…Filter adsorption artifact is thought to be by either adhesion of organic gas molecules or adsorption of particle converted from gas onto the filter media. The contribution of mass by each mechanism is subject to multiple parameters such as filter face velocity, filter/ gas temperature, soot loading etc (Högström et al, 2012). Chase et al (2004) studied the effect of filter media and temperature on filter adsorption artifact for the measurement of vehicle PM emissions.…”

Fuel-Operated Auxiliary Heaters Are a Major Additional Source of Vehicular Particulate Emissions in Cold Regions

“…Previous studies have only focused on improving the thermal efficiency or fuel economy of the heaters [6]. Conversely, AHs have also been used as artificial soot generators in laboratories after modifying their combustion parameters [7], which do not represent normal use emissions.…”