Non-volatile Particle Research Articles

Effect of Sampling Conditions on the Sub-23 nm Nonvolatile Particle Emissions Measurements of a Moped

The solid (or nonvolatile) particle number (SPN) emissions of light-duty and heavy-duty vehicles and engines are regulated in the European Union. The measurements are conducted from the tailpipe during on-road tests, but from the dilution tunnel in the laboratory under controlled conditions. Recently, dedicated laboratory studies for the evaluation of the measurement uncertainty at the two sampling locations found differences due to the formation of nonvolatile particles, i.e., particles that do not evaporate in the thermal pre-treatment part of the particle number systems. In order to investigate the origin of these particles, measurements at the tailpipe, the transfer tube, and the dilution tunnel were conducted with cold and hot dilution and instruments with different lower detection limits (4 nm, 10 nm, and 23 nm). The results showed that sub-23 nm nonvolatile particles could be detected in the dilution tunnel, but not at the tailpipe, due to growth of low volatility compounds in the transfer tube and the finite residence time in the thermal pretreatment part of the particle number systems. When measuring below 23 nm, diluting at the tailpipe or reducing the residence time in the transfer tube to the dilution tunnel is important in order to minimize such differences.

European Regulatory Framework and Particulate Matter Emissions of Gasoline Light-Duty Vehicles: A Review

The particulate matter (PM) emissions of gasoline vehicles were much lower than those of diesel vehicles until the introduction of diesel particulate filters (DPFs) in the early 2000s. At the same time, gasoline direct injection (GDI) engines started to become popular in the market due to their improved efficiency over port fuel injection (PFI) ones. However, the PM mass and number emissions of GDI vehicles were higher than their PFI counterparts and diesel ones equipped with DPFs. Stringent PM mass levels and the introduction of particle number limits for GDI vehicles in the European Union (EU) resulted in significant PM reductions. The EU requirement to fulfill the proposed limits on the road resulted to the introduction of gasoline particulate filters (GPFs) in EU GDI models. This review summarizes the evolution of PM mass emissions from gasoline vehicles placed in the market from early 1990s until 2019 in different parts of the world. The analysis then extends to total and nonvolatile particle number emissions. Care is given to reveal the impact of ambient temperature on emission levels. The discussion tries to provide scientific input to the following policy-relevant questions. Whether particle number limits should be extended to gasoline PFI vehicles, whether the lower limit of 23 nm for particle number measurements should be decreased to 10 nm, and whether low ambient temperature tests for PM should be included.

Differences between tailpipe and dilution tunnel sub-23 nm nonvolatile (solid) particle number measurements

AbstractEuropean Union vehicle and engine regulations require measurement of nonvolatile (solid) particles with diameter >23 nm at the dilution tunnel. In 2019 it was decided to include particles >...

Effect of selective catalytic reduction on exhaust nonvolatile particle emissions of Euro VI heavy-duty compression ignition vehicles

The nonvolatile particle number (PN) emissions of late technology diesel heavy-duty vehicles (HDV) are very low due to the introduction of Diesel Particulate Filters (DPF). Nevertheless, a large fraction (50%) of particles below the current lower regulated size (23 nm) was recently reported. Moreover, large differences between laboratory and PN Portable Emission Measurement Systems (PN-PEMS) have been observed. In order to better understand such differences, the physical properties of the exhaust aerosol from two Euro VI technology diesel heavy-duty engines were studied. It was found that urea injection leads to formation of nonvolatile particles. The produced particles covered a wide size range spanning from below 10 nm to above 100 nm. As such, they contribute to the regulated PN emissions, with measured concentrations corresponding to as high as 2 × 1011 #/kWh over a World Harmonized Transient Cycle (WHTC). However, a large fraction of them was undetected owing to their small particle size. Low-cutoff size (10 nm) Condensation Particle Counters (CPCs) (which are under discussion to be included in the regulations) measured up to twice as high concentrations. Considering the large particle losses in the sampling systems at this size range, the true concentrations can be two times higher from what the low-cutoff CPCs reported. When the temperature of the SCR system exceeded a threshold of 300 °C, the produced particles were found to be positively charged, increasing the average exhaust aerosol charge up to +3 elementary charges per particle. Scanning Mobility Particle Sizer (SMPS) measurements of non-neutralized samples revealed that even the smallest of them can carry more than one positive charge. The findings of this study can explain the differences reported between PEMS and laboratory systems and especially those based on diffusion charging. They also provide insight for a refinement of technical requirements prescribed in the European PEMS regulation to more accurately quantify the PN emissions from such technologies.

Experimental Assessment of an Electrofilter and a Tandem Positive-Negative Corona Charger for the Measurement of Charged Nanoparticles formed in Selective Catalytic Reduction Systems

Onboard measurement of non-volatile particle number (PN) emissions with portable emissions measurement systems (PEMS) was introduced for the type-approval of passenger cars in Europe since 2017 and is foreseen for heavy-duty (HD) vehicles in 2021. First studies on the performance of PN-PEMS with HD engine exhaust revealed larger differences between established PN-PEMS techniques than what was observed for passenger cars. Particles forming in selective catalytic reduction (SCR) systems for NOx of late technology HD engines have recently been identified as a potential reason for the observed differences. The formed particles have a size distribution peaking below the regulatory limit of 23 nm and most importantly acquire high (more than one) positive charges at the elevated exhaust temperatures. Precise measurement of such highly charged nanosized particles with PN-PEMS instrumentation utilizing diffusion charger (DC) based counters requires proper conditioning of these charges. Two approaches were investigated in this study: (a) an electrofilter (EF) to completely remove charged particles below the regulated size and (b) a tandem negative-positive corona (TC) charger to directly condition pre-charged particles. The two technical solutions were tested alongside the unmodified DC-based PN-PEMS, a PN-PEMS utilizing a condensation particle counter (CPC) and a reference stationary PN system using exhaust of two SCR-equipped HD engines. The results confirmed that the particles forming in such SCR systems are responsible for the observed inconsistencies and that both technical solutions efficiently address the interferences of these pre-charged nanoparticles.

Non-volatile particle emissions from aircraft turbine engines at ground-idle induce oxidative stress in bronchial cells

Aircraft emissions contribute to local and global air pollution. Health effects of particulate matter (PM) from aircraft engines are largely unknown, since controlled cell exposures at relevant conditions are challenging. We examined the toxicity of non-volatile PM (nvPM) emissions from a CFM56-7B26 turbofan, the world’s most used aircraft turbine using an unprecedented exposure setup. We combined direct turbine-exhaust sampling under realistic engine operating conditions and the Nano-Aerosol Chamber for In vitro Toxicity to deposit particles onto air–liquid-interface cultures of human bronchial epithelial cells (BEAS-2B) at physiological conditions. We evaluated acute cellular responses after 1-h exposures to diluted exhaust from conventional or alternative fuel combustion. We show that single, short-term exposures to nvPM impair bronchial epithelial cells, and PM from conventional fuel at ground-idle conditions is the most hazardous. Electron microscopy of soot reveals varying reactivity matching the observed cellular responses. Stronger responses at lower mass concentrations suggest that additional metrics are necessary to evaluate health risks of this increasingly important emission source.

Particulate Mass and Nonvolatile Particle Number Emissions from Marine Engines Using Low-Sulfur Fuels, Natural Gas, or Scrubbers.

In order to meet stringent fuel sulfur limits, ships are increasingly utilizing new fuels or, alternatively, scrubbers to reduce sulfur emissions from the combustion of sulfur-rich heavy fuel oil. The effects of these methods on particle emissions are important, because particle emissions from shipping traffic are known to have both climatic and health effects. In this study, the effects of lower sulfur level liquid fuels, natural gas (NG), and exhaust scrubbers on particulate mass (PM) and nonvolatile particle number (PN greater than 23 nm) emissions were studied by measurements in laboratory tests and in use. The fuel change to lower sulfur level fuels or to NG and the use of scrubbers significantly decreased the PM emissions. However, this was not directly linked with nonvolatile PN emission reduction, which should be taken into consideration when discussing the health effects of emitted particles. The lowest PM and PN emissions were measured when utilizing NG as fuel, indicating that the use of NG could be one way to comply with up-coming regulations for inland waterway vessels. Low PN levels were associated with low elemental carbon. However, a simultaneously observed methane slip should be taken into consideration when evaluating the climatic impacts of NG-fueled engines.

Size distribution of vehicle emitted primary particles measured in a traffic tunnel

Total and size-resolved concentrations and emission factors are used to compare fleet-averaged vehicle emissions in Pittsburgh, PA in 2002 and 2014. Winter-time traffic tunnel measurements acquired using dual scanning mobility particle sizers (SMPS) over the size range 3–500 nm form the key input for the analysis. Size-resolved mass emission factors were calculated assuming a nanoparticle aggregate model. The ultrafine particle (<30 nm) emissions of diesel vehicles significantly dropped from 2002 to 2014. In the 2014 study, a thermodenuder (TD) was deployed together with the SMPS to measure emissions of non-volatile particles. After evaporation at 250 °C inside the TD, the median diameter of the number-size distribution shifted from 16 nm to ∼7 nm. The total particle number decreased significantly (69%) after evaporating inside the TD, indicating that vehicle emitted particles may be largely externally mixed and that a large fraction of these particles may be purely composed of volatile components. Based on the SMPS-TD measurements, we report a size-resolved volatile-to-non-volatile-component-ratio for vehicle emitted particles. It shows that smaller particles (10–60 nm) emitted by vehicles are dominantly (over 75%) composed of volatile components. We also apportioned the size-resolved particles and non-volatile particle mass and number emission factors for both gasoline and diesel vehicles. Diesel vehicles emitted significantly more ultrafine particles and non-volatile particles than gasoline vehicles.

Take-off engine particle emission indices for in-service aircraft at Los Angeles International Airport

We present ground-based, advected aircraft engine emissions from flights taking off at Los Angeles International Airport. 275 discrete engine take-off plumes were observed on 18 and 25 May 2014 at a distance of 400 m downwind of the runway. CO2 measurements are used to convert the aerosol data into plume-average emissions indices that are suitable for modelling aircraft emissions. Total and non-volatile particle number EIs are of order 1016–1017 kg−1 and 1014–1016 kg−1, respectively. Black-carbon-equivalent particle mass EIs vary between 175–941 mg kg−1 (except for the GE GEnx engines at 46 mg kg−1). Aircraft tail numbers recorded for each take-off event are used to incorporate aircraft- and engine-specific parameters into the data set. Data acquisition and processing follow standard methods for quality assurance. A unique aspect of the data set is the mapping of aerosol concentration time series to integrated plume EIs, aircraft and engine specifications, and manufacturer-reported engine emissions certifications. The integrated data enable future studies seeking to understand and model aircraft emissions and their impact on air quality.

Influence of biomass burning on mixing state of sub-micron aerosol particles in the North China Plain

Particulate emissions from crop residue burning decrease the air quality as well as influence aerosol radiative properties on a regional scale. The North China Plain (NCP) is known for the large scale biomass burning (BB) of field residues, which often results in heavy haze pollution episodes across the region. We have been able to capture a unique BB episode during the international CAREBeijing-NCP intensive field campaign in Wangdu in the NCP (38.6°N, 115.2°E) from June to July 2014. It was found that aerosol particles originating from this BB event showed a significantly different mixing state compared with clean and non-BB pollution episodes. BB originated particles showed a narrower probability density function (PDF) of shrink factor (SF). And the maximum was found at shrink factor of 0.6, which is higher than in other episodes. The non-volatile particle number fraction during the BB episode decreased to 3% and was the lowest measured value compared to all other predefined episodes. To evaluate the influence of particle mixing state on aerosol single scattering albedo (SSA), SSA at different RHs was simulated using the measured aerosol physical-chemical properties. The differences between the calculated SSA for biomass burning, clean and pollution episodes are significant, meaning that the variation of SSA in different pollution conditions needs to be considered in the evaluation of aerosol direct radiative effects in the NCP. And the calculated SSA was found to be quite sensitive on the mixing state of BC, especially at low-RH condition. The simulated SSA was also compared with the measured values. For all the three predefined episodes, the measured SSA are very close to the calculated ones with assumed mixing states of homogeneously internal and core-shell internal mixing, indicating that both of the conception models are appropriate for the calculation of ambient SSA in the NCP.

VH-TDMA: A description and verification of an instrument to measure aerosol particle hygroscopicity and volatility

ABSTRACTThe aim of this study was to provide a description and characterize the performance of a volatility hygroscopicity tandem differential mobility analyzer (VH-TDMA) by calibration measurements. In our investigations, we used the two calibration standards most often used by the TDMA community: ammonium sulfate ((NH4)2SO4) and sodium chloride (NaCl) particles. The hygroscopic growth factors, volatility factors, and the hygroscopic growth factors of the nonvolatile particle core were measured in different relative humidity and thermal denuder temperature conditions. The measured hygroscopic growth and deliquescence relative humidities for ammonium sulfate and sodium chloride particles are in line with theory and results from previous measurements, as are the measurements for volatility and hygroscopicity of the particle core. We summarize the measurement campaigns, where the VH-TDMA has been deployed, and show the instrument is capable of measuring high quality data of atmospheric particle properties i...

Measurement of nonvolatile particle number size distribution

Abstract. An experimental methodology was developed to measure the nonvolatile particle number concentration using a thermodenuder (TD). The TD was coupled with a high-resolution time-of-flight aerosol mass spectrometer, measuring the chemical composition and mass size distribution of the submicrometer aerosol and a scanning mobility particle sizer (SMPS) that provided the number size distribution of the aerosol in the range from 10 to 500 nm. The method was evaluated with a set of smog chamber experiments and achieved almost complete evaporation (&gt; 98 %) of secondary organic as well as freshly nucleated particles, using a TD temperature of 400 °C and a centerline residence time of 15 s. This experimental approach was applied in a winter field campaign in Athens and provided a direct measurement of number concentration and size distribution for particles emitted from major pollution sources. During periods in which the contribution of biomass burning sources was dominant, more than 80 % of particle number concentration remained after passing through the thermodenuder, suggesting that nearly all biomass burning particles had a nonvolatile core. These remaining particles consisted mostly of black carbon (60 % mass contribution) and organic aerosol (OA; 40 %). Organics that had not evaporated through the TD were mostly biomass burning OA (BBOA) and oxygenated OA (OOA) as determined from AMS source apportionment analysis. For periods during which traffic contribution was dominant 50–60 % of the particles had a nonvolatile core while the rest evaporated at 400 °C. The remaining particle mass consisted mostly of black carbon with an 80 % contribution, while OA was responsible for another 15–20 %. Organics were mostly hydrocarbon-like OA (HOA) and OOA. These results suggest that even at 400 °C some fraction of the OA does not evaporate from particles emitted from common combustion processes, such as biomass burning and car engines, indicating that a fraction of this type of OA is of extremely low volatility.

Effects of fresh lubricant oils on particle emissions emitted by a modern gasoline direct injection passenger car.

Particle emissions from a modern turbocharged gasoline direct injection passenger car equipped with a three-way catalyst and an exhaust gas recirculation system were studied while the vehicle was running on low-sulfur gasoline and, consecutively, with five different lubrication oils. Exhaust particle number concentration, size distribution, and volatility were determined both at laboratory and on-road conditions. The results indicated that the choice of lubricant affected particle emissions both during the cold start and warm driving cycles. However, the contribution of engine oil depended on driving conditions being higher during acceleration and steady state driving than during deceleration. The highest emission factors were found with two oils that had the highest metal content. The results indicate that a 10% decrease in the Zn content of engine oils is linked with an 11-13% decrease to the nonvolatile particle number emissions in steady driving conditions and a 5% decrease over the New European Driving Cycle. The effect of lubricant on volatile particles was even higher, on the order of 20%.

Particle number emission factors and volatile fraction of particles emitted from on-road gasoline direct injection passenger vehicles

Particle number emission factors, and the volatility of the particles, are measured on-road for five gasoline direct injection vehicles over a wide range of operating conditions including urban and highway driving conditions. Two condensation particle counters (CPC) were used to measure nascent and non-volatile (thermodenuded) particle concentrations for transient urban and highway tests. To measure the non-volatile concentration and also the volatility of the particles, a thermodenuder was employed to remove the semi-volatile material from the aerosol sample. Rapid accelerations were also studied in more detail by measuring the particle size distributions in real-time using a differential mobility spectrometer (DMS). The ratio of semi-volatile particles to total particle number is generally higher during acceleration followed by the idle operating mode. The number emission factors (for particles larger than 2.5 nm) ranged between 5.46 × 1011–3.50 × 1012/km for freshly emitted (nascent) particles and between 2.87 × 1011–3.31 × 1012/km for non-volatile (thermodenuded) particles. More particles per kilometer are produced during acceleration compared to cruise conditions where the non-volatile particle number emission factor for acceleration is 2.3 and 1.8 times higher than vehicle cruise for urban and highway driving cycles, respectively. Particle number emission factor models are also presented in terms of particle emission rate as a function of vehicle tractive power and also as a function of vehicle specific power as defined for the US Environmental Protection Agency's MOVES model.

Chemical mass balance of 300 °C non-volatile particles at the tropospheric research site Melpitz, Germany

Abstract. In the fine-particle mode (aerodynamic diameter &lt; 1 μm) non-volatile material has been associated with black carbon (BC) and low-volatile organics and, to a lesser extent, with sea salt and mineral dust. This work analyzes non-volatile particles at the tropospheric research station Melpitz (Germany), combining experimental methods such as a mobility particle-size spectrometer (3–800 nm), a thermodenuder operating at 300 °C, a multi-angle absorption photometer (MAAP), and an aerosol mass spectrometer (AMS). The data were collected during two atmospheric field experiments in May–June 2008 as well as February–March 2009. As a basic result, we detected average non-volatile particle–volume fractions of 11 ± 3% (2008) and 17 ± 8% (2009). In both periods, BC was in close linear correlation with the non-volatile fraction, but not sufficient to quantitatively explain the non-volatile particle mass concentration. Based on the assumption that BC is not altered by the heating process, the non-volatile particle mass fraction could be explained by the sum of black carbon (47% in summer, 59% in winter) and a non-volatile organic contribution estimated as part of the low-volatility oxygenated organic aerosol (LV-OOA) (53% in summer, 41% in winter); the latter was identified from AMS data by factor analysis. Our results suggest that LV-OOA was more volatile in summer (May–June 2008) than in winter (February–March 2009) which was linked to a difference in oxidation levels (lower in summer). Although carbonaceous compounds dominated the sub-μm non-volatile particle mass fraction most of the time, a cross-sensitivity to partially volatile aerosol particles of maritime origin could be seen. These marine particles could be distinguished, however from the carbonaceous particles by a characteristic particle volume–size distribution. The paper discusses the uncertainty of the volatility measurements and outlines the possible merits of volatility analysis as part of continuous atmospheric aerosol measurements.

Heavy-duty, off-road diesel engine low-load particle number emissions and particle control

Exhaust gas particle and ion size distributions were measured from an off-road diesel engine complying with the European Stage IIIB emission standard. The measurements were performed at idling and low load conditions on an engine dynamometer. Nucleation-mode particles dominated the diesel exhaust particle number emissions at idle load. The nonvolatile nucleation-mode geometric mean diameter was detected at 10 nm or below. The nonvolatile nucleation-mode charge state implied that it has evolved through a highly ionizing environment before emission from the engine. The determined charging probabilities were 10.0 ± 2.2% for negative and 8.0 ± 2.0% for positive polarity particles. The nonvolatile nucleation particle concentration and size was also shown to be dependent on the lubricant oil composition. The particle emissions were efficiently controlled with a partial filter or with partial filter + selective catalytic reduction (SCR) combination. The particle number removal efficiencies of the aftertreatment systems were over 95% for wet total particle number (>3nm) and over 85% for dry particle total number. Nevertheless, the aftertreatment systems’ efficiencies were around 50% for the soot-mode particles. The low-load nonvolatile nucleation particle emissions were also dependent on the engine load, speed, and fuel injection pressure. The low load particle number emissions followed the soot-core trade-off, similar to medium or high operating loads.Implications:Idling and low-load diesel engine exhaust emissions affect harmfully the ambient air quality. The low-load particle number emissions are here shown to peak in the 10-nm size range for a modern off-road engine. The particles are electrically charged and nonvolatile and they originate from the combustion process. Tailpipe particle control by open channel filter can remove more than 85% of the nonvolatile 10-nm particles and about 50% of the soot-mode particles, while the fuel injection pressure increase can lead to particle number increase. The study provides a new viewpoint for low-load particle emissions and control.

Particulate matter characteristics of a light-duty diesel engine with alternative fuel blends

The non-volatile particle emission characteristics of alternative (rapeseed methyl ester and gas-to-liquid) diesel fuel blends were studied through an experimental investigation carried out on a light-duty common-rail diesel engine. A blend ratio of 10 vol % was chosen as the practical limit for biodiesels in this study, and the research focus was on the particle number concentration and size distribution with various injection strategies, in which the non-volatile emissions were measured using thermodilution. The particle morphology and mass, together with the related gaseous emissions, were measured and analysed. The results indicate that, without any engine modification, adding selected alternative fuels even at a low percentage could result in a favourable reduction in the number of particles and in a significant reduction in the total particle concentration in both the nucleation mode and the accumulation mode. The particle emissions of the three fuels demonstrated monomodal size distributions under most engine conditions tested, except for the engine idling case, which produced a bimodal size distribution. The influence of 10 vol % rapeseed methyl ester or gas-to-liquid diesel blends on the carbon monoxide and nitrogen oxide emissions is not significant. Nevertheless, using these diesel fuel blends may increase the total hydrocarbon emissions and may lead to high particulate matter emissions.

Non-volatile particle characteristics of a light-duty diesel engine with pilot injections and exhaust gas recirculation

A pilot injection has been used widely in diesel engines for the control of nitrogen oxide emissions and noise. However, very little information on the characteristics of particulate matter emissions with a pilot injection is available. In this paper, the non-volatile particle emissions of a light-duty common-rail production diesel engine under the impact of a pilot injection are studied in terms of the particle number concentration and the particle size distribution with the measurements taken with a scanning mobility particle sizer. For various key parameters such as the fuel quantity and the injection timing, the results illustrate how a pilot injection alongside a main injection could affect particulate matter emissions, which are also shown to be closely related to the engine mode and the exhaust gas recirculation level. It is revealed that advancing the pilot injection generally reduces the number and size of particles in both the accumulation mode and the nucleation mode. It is also found that an increase in the pilot fuel quantity increases the total number and size of particles, with a significant impact on the number of accumulation-mode particles, which overwhelms the decrease in the number of nucleation-mode particles.

Heated submicron particle fluxes using an optical particle counter in urban environment

Abstract. From May 2008 to March 2009 aerosol emissions were measured using the eddy covariance method covering the size range 0.25 to 2.5 μm diameter (Dp) from a 105 m tower, in central Stockholm, Sweden. Supporting chemical aerosol data were collected at roof and street level. Results show that the inorganic fraction of sulfate, nitrate, ammonium and sea salt accounts for approximately 15% of the total aerosol mass &lt; 1 μm Dp (PM1) with water soluble soil contributing 11% and water insoluble soil 47%. Carbonaceous compounds were at the most 27% of PM1 mass. It was found that heating the air from the tower to 200 °C resulted in the loss of approximately 60% of the aerosol volume at 0.25 μm Dp whereas only 40% of the aerosol volume was removed at 0.6 μm Dp. Further heating to 300 °C caused very little additional losses &lt;0.6 μm Dp. The chemical analysis did not include carbonaceous compounds, but based on the difference between the total mass concentration and the sum of the analyzed non-carbonaceous materials, it can be assumed that the non-volatile particulate material (heated to 300 °C) consists mainly of carbonaceous compounds, including elemental carbon. Furthermore, it was found that the non-volatile particle fraction &lt;0.6 μm Dp correlated (r2 = 0.4) with the BC concentration at roof level in the city, supporting the assumption that the non-volatile material consists of carbonaceous compounds. The average diurnal cycles of the BC emissions from road traffic (as inferred from the ratio of the incremental concentrations of nitrogen oxides (NOx) and BC measured on a densely trafficked street) and the fluxes of non-volatile material at tower level are in close agreement, suggesting a traffic source of BC. We have estimated the emission factors (EFs) for non-volatile particles &lt;0.6 μm Dp to be 2.4 ± 1.4 mg veh−1 km−1 based on either CO2 fluxes or traffic activity data. Light (LDV) and heavy duty vehicle (HDV) EFs were estimated using multiple linear regression and reveal that for non-volatile particulate matter in the 0.25 to 0.6 μm Dp range, the EFHDV is approximately twice as high as the EFLDV, the difference not being statistically significant.

Classification of Volatile Engine Particles

Volatile particles cannot be detected at the engine exhaust by an aerosol detector, as they are formed when the exhaust is mixed downstream with the ambient air. The lack of a precise definition of volatile engine particles has been an impediment to engine manufacturers and regulatory agencies involved in the development of effective control strategies. Volatile particles from combustion sources contribute to the atmospheric particulate burden, and this is a critical issue in ongoing research in the areas of air quality and climate change. A new instrument, called a volatile particle separator (VPS), is developed in this work. It utilizes a proprietary microporous metallic membrane to separate particles from vapors. VPS data are used in the development of a two-parameter function to quantitatively classify, for the first time, the volatilization behavior of engine particles. The value of parameter “A” describes the volatilization potential of an aerosol. A nonvolatile particle has a larger A-value than a volatile one. The value of parameter “k,” an effective evaporation energy barrier, is found to be much smaller for small engine particles than for large engine ones. The VPS instrument is not simply a volatile particle remover, as it makes possible the characterization of volatile engine particles in numerical terms.