PM Measurement Artifact: Organic Vapor Deposition on Different Filter Media

Self Cite

The electrical low pressure impactor (ELPI) is a useful tool for recording transient particle size distributions, such as in motor vehicle emissions. But for sub-micron aerosols, the straightforward mass weighting and integration of these size distributions overestimates the particulate matter (PM) mass by a factor of two or more. The present article examines the sources of this discrepancy and develops an analysis that allows quantitative PM mass measurement with an accuracy of about 20%. This procedure is applied to measure motor vehicle PM emissions, and the results are compared with filter-based gravimetric determinations. Good agreement is achieved for diesel and direct injection gasoline vehicles. For particulate trap equipped diesel vehicles and conventional gasoline vehicles, the PM mass recorded by the ELPI is often substantially lower than the filter based mass owing to the gaseous adsorption artifact of the latter. Accurate work at very low emissions levels, less than ∼1 mg/mi, requires further study of how reliably the ELPI can provide semivolatile nanoparticle mass as well as an improved understanding of filter-based vehicle exhaust measurement.

Section: Figmentioning

confidence: 99%

Measuring Particulate Mass Emissions with the Electrical Low Pressure Impactor

Maricq

Chase

2006

Self Cite

“…It can also be used to convert particle size distributions to particle mass distributions from which total particle mass concentration can be determined. The integrated particle size distribution (IPSD) method is seen as an option for particle mass emission factor measurement for the modern vehicles (Liu et al 2009(Liu et al , 2012, which produce very few particles and where gravimetric measurement is difficult due to the low mass collected and the significance of errors due to sampling artifacts (Chase et al 2004). The effective density function for GDI particles has been measured by Maricq and Xu (2004), Symonds et al (2008), and Quiros et al (2015).…”

Section: Introductionmentioning

confidence: 99%

Effective Density and Volatility of Particles Emitted from Gasoline Direct Injection Vehicles and Implications for Particle Mass Measurement

Momenimovahed

Olfert

2015

The effective density and volatility of particulate emissions from five gasoline direct injection (GDI) passenger vehicles were measured using a tandem differential mobility analyzer (DMA) and centrifugal particle mass analyzer (CPMA) system. The measurements were conducted on a chassis dynamometer at three steady-state operating conditions. A thermodenuder was employed to find the volatility and mixing state of the particles as well as the effective density of nascent and non-volatile particles (defined as particle phase remaining after denuding at 200 C). The mass-mobility exponent ranged between 2.4 and 2.7 for nascent (or undenuded) particles and between 2.5 and 2.7 for non-volatile particles; higher than typical diesel soot. The effective density function was 4278d m ¡0.438 § 76.3 kg/m 3 (for mobility diameter, d m , in nm) for nascent particles and 3215d m ¡0.395 § 37.9 kg/m 3 for non-volatile particles. The effective density functions of the non-volatile particles were fairly similar for the conditions studied. The uncertainty in using the effective density and mixing state data to determine the mass concentration of the aerosol by integrating mobility size distributions was examined. The uncertainty in mass concentration is minimized when only the non-volatile component is measured. However, the uncertainty in the mass concentration increases substantially if nascent particles are measured due to uncertainties in the particle mixing state and their associated effective densities. Furthermore, transient vehicle operation (cold-starts, accelerations, and decelerations) would likely change the mixing state of the exhaust particles suggesting it is difficult to accurately measure the mass concentration of undenuded GDI exhaust particulate using integrated size distribution methods.

“…Quartz fiber filters have been found to be prone to filter artifacts (Schauer et al 1999;Lipsky and Robinson 2006), and therefore, current legislation recommends using Teflon-coated glass fiber or membrane filters for PM exhaust measurements. However, recent studies show that Teflon filters also suffer from sampling artifacts (Chase et al 2004;Khalek 2005 artifact of 10%-20% for Teflon membrane filters and 30%-50% for Teflon-coated glass fiber filters. The positive artifact is believed to be dominant over the negative one when sampling diluted vehicle exhaust (Chase et al 2004).…”

Section: Introductionmentioning

confidence: 99%

“…However, recent studies show that Teflon filters also suffer from sampling artifacts (Chase et al 2004;Khalek 2005 artifact of 10%-20% for Teflon membrane filters and 30%-50% for Teflon-coated glass fiber filters. The positive artifact is believed to be dominant over the negative one when sampling diluted vehicle exhaust (Chase et al 2004).…”

Section: Introductionmentioning

confidence: 99%

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

Högström

Karjalainen

Yli-Ojanperä

et al. 2012

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.