Response Characteristics of the Particle Measuring Systems Active Scattering Aerosol Spectrometer Probes

Predictions of the size response of various light-scattering aerosol counters manufactured by Particle Measuring Systems are reported. Models that exploit the high intensity of light available within the cavity of a He-Ne gas laser (generically referred to by the manufacturer as ''active scattering aerosol spectrometer probes'') are considered. The new response function properly averages over particle trajectories through nodes, antinodes, and intermediate regions of the intracavity laser beam. Our studies address probes having two basic scattering geometries: those that collect light scattered over a relatively narrow solid angle (subtending angles between 4° and 22° from the laser beam axis, as in the model ASASP-300 and ASASP-300X probes) and those that collect light over a rather large solid angle (between 35° and 120° , as in the ASASP-X, ASASP-100X, LAS-250X, LAS-X, and HS-LAS probes). The theoretical response predictions for both narrow-angle and wide-angle probes are compared to previous measurements of monodisperse test aerosols of polystyrene latex, dyoctylphthalate, nigrosin dye, and carbon black. The new response function predicts smoother dependence on particle size than the previous response function of Pinnick and Auvermann (1979) and is in better agreement with measurement. Response calculations for common atmospheric aerosol (water, sulfuric acid, ammonium sulfate, and black carbon) reveal the considerable sensitivity of the response to particle dielectric properties. Response functions for internal mixtures (black carbon inclusions in water droplets, quartz in sulfuric acid, carbon in ammonium sulfate, and metal in sulfuric acid) are somewhat different than those for homogeneous particles. Comparison of response calculations with the manufacturer's calibration reveal conditions for which the manufacturer's calibration is most appropriate and the potential for errors (as much as a factor of two in sizing) when it is blindly applied. Finally, response functions for multiline laser operation, as the manufacturer suggests might be appropriate for the HS-LAS and LAS-X probes, are nearly the same as for single-line lasing. These results should help the user of these instruments to more realistically interpret size distribution measurements.     

Calibration Correction of an Active Scattering Spectrometer Probe to Account for Refractive Index of Stratospheric Aerosols: Comparison of Results with Inertial Impaction

Real-time particle size spectra are being acquired on our research aircraft with relative ease and speed by techniques that make use of the real-time interaction of laser light with aerosols and cloud droplets. The results are, however, sometimes ambiguous, because the optical “signatures” of the particles depend on their refractive indices in addition to physical dimensions. The calibration supplied by the manufacturer is based on instrument response to a specific test aerosol, e.g., latex spheres (refractive index = 1.59). Such a calibration is strictly valid only for sample aerosols of refractive index and shape similar to the test aerosol. Whenever the sample aerosol differs from the test aerosol, a calibration correction is in order. Of concern here is the use of an active scattering spectrometer probe (ASAS-X), to measure sulfuric acid aerosols on high-flying U-2 and ER-2 research aircraft. Correcting the calibration of the ASAS-X for dilute sulfuric acid droplets (refractive index = 1.44) that predominate the stratospheric aerosol changes the inferred sizes by up to 32% per size interval from that determined from the nominal calibration. This results in an average increase in particle surface area and volume of 42 ± 10% and 71 ± 19%, respectively. The calibration correction of the optical spectrometer probe for stratospheric aerosol is validated by independent and simultaneous sampling of the particles with impactors. Sizing and counting of particles on microphotographs of scanning electron microscope images give results on total particle surface areas and volumes. After the calibration correction, the optical spectrometer data (averaged over four size distributions) agree with the impactor results (similarly averaged) to within a few percent. We conclude that the optical properties, or chemical makeup, of the sample aerosol must be known for accurate size analysis by optical aerosol spectrometers.     

Response of Particle Measuring Systems Airborne ASASP and PCASP to NaCl and Latex Particles

The response of a Particle Measuring Systems, Inc. (PMS) airborne Passive Cavity Aerosol Spectrometer Probe (PCASP)-100X and a PMS airborne Active Scattering Aerosol Spectrometer Probe (ASASP)-100X to nearly monodisperse aerosols of NaCl and polystyrene latex spheres in the size range 0.074–1.07 μm diameter (± 5%) are examined. Particles < 0.34 μm are size classified by electrical mobility using a Thermo System Inc. Electrostatic Classifier. The particles are also sized with the aid of a scanning electron microscope. Three equivalent diameters for the near cubic NaCl particles are considered: average of length and breadth, and cross section equivalent and volume equivalent diameters. For the linear diameter, the probes' response to latex and NaCl particles is quite similar. However, the use of cross section and volume equivalent diameter leads NaCl to be sized significantly less than the latex spheres consistent with reported differences between spherical (i.e., latex) and cubical geometry (i.e., NaCl). Using the linear diameter the lower detection limit of the ASASP-100X is found to be 0.175 μm ±5%, not 0.120 μm as given by the manufacturer. The lower detection limit of the PCASP-100X is found to be 0.125 μm ±5%, compared with the value of 0.10 μm suggested by PMS. In spite of this discrepancy the PCASP still represents a significant advancement for the airborne measurement of aerosol size distributions. Size distributions measured simultaneously with the two probes from an aircraft agreed more favorably with the new calibrations than with those of the manufacturer.     

Backscatter of light by aerosols at high relative humidity

The optical backscattering as well as extinction coefficients of a model aerosol are computed for relative humidity between 0.80 and 0.995. The model aerosol at this humidity range consists of droplets of salt solution surrounding a water-insoluble nucleus. This layered structure is taken into account in determining the refractive index of the solution, but the scattering is approximated by the ordinary Mie theory of homogeneous particles. The size distribution consists of the sum of two logarithmic normal distributions corresponding to the size ranges of small and large particles. The resulting scattering coefficients are smooth and steadily growing functions of relative humidity, with some dependence on wavelength and size distribution.     

Rapid,Size-Resolved Aerosol Hygroscopic Growth Measurements: Differential Aerosol Sizing and Hygroscopicity Spectrometer Probe (DASH-SP)

We report on a new instrument developed to perform rapid, size-resolved aerosol hygroscopicity measurements. The differential aerosol sizing and hygroscopicity spectrometer probe (DASH-SP) employs differential mobility analysis in-concert with multiple humidification and optical sizing steps to determine dry optical size and hygroscopic growth factors for size-selected aerosols simultaneously at three elevated relative humidities. The DASH-SP has been designed especially for aircraft-based measurements, with time resolution as short as a few seconds. The minimum particle diameter detected with 50% efficiency in the optical particle counters (OPCs) is 135 ± 8 nm, while the maximum detectable particle diameter is in excess of 1 μm. An iterative data processing algorithm quantifies growth factors and “effective” refractive indices for humidified particles using an empirically derived three-dimensional surface (OPC pulse height–refractive index–particle size), based on a calculated value of the “effective” dry particle refractive index. Excellent agreement is obtained between DASH-SP laboratory data and thermodynamic model predictions for growth factor dependence on relative humidity for various inorganic salts. Growth factor data are also presented for several organic acids. Oxalic, malonic, glutaric, and glyoxylic acids grow gradually with increasing relative humidity up to 94%, while succinic and adipic acids show no growth. Airborne measurements of hygroscopic growth factors of ship exhaust aerosol during the 2007 Marine Stratus/Stratocumulus Experiment (MASE II) field campaign off the central coast of California are presented as the first report of the aircraft integration of the DASH-SP.     

Evaluation of Composition-Dependent Collection Efficiencies for the Aerodyne Aerosol Mass Spectrometer using Field Data

In recent years, Aerodyne aerosol mass spectrometers (AMS) have been used in many locations around the world to study the size-resolved, nonrefractory chemical composition of ambient particles. In order to obtain quantitative data, the mass or (number) of particles detected by the AMS relative to the mass (or number) of particles sampled by the AMS, i.e., the AMS collection efficiency (CE) must be known. Previous studies have proposed and used parameterizations of the AMS CE based on the aerosol composition and sampling line relative humidity. Here, we evaluate these parameterizations by comparing AMS mass concentrations with independent measurements of fine particle volume or particle-into-liquid sampler (PILS) ion chromatography measurements for 3 field campaigns with different dominant aerosol mixtures: (1) acidic sulfate particles, (2) aerosol containing a high mass fraction of ammonium nitrate, and (3) aerosol composed of primarily biomass burning emissions. The use of the default CE of 0.5 for all campaigns resulted in 81–90% of the AMS speciated and total mass concentrations comparing well with fine particle volume or PILS measurements within experimental uncertainties, with positive biases compared with a random error curve. By using composition-dependent CE values (sometimes as a function of size) which increased the CE for the above aerosol types, the fraction of data points within the measurement uncertainties increased to more than 92% and the mass concentrations decreased by ～5–15% on an average. The CE did not appear to be significantly dependent on changes in organic mass fraction although it was substantial in the 3 campaigns (47, 30, and 55%).

Copyright 2012 American Association for Aerosol Research     

Effects of RH on Glass Microfiber Filtration Efficiency for Airborne Bacteria and Bacteriophage Over Time

This study investigated the removal efficiency of viable signals of aerosolized bacteria and viruses, stabilized with respect to relative humidity, by simple glass microfiber filters. When examined over an extended time period, relative humidity affected both the size distribution of the stabilized aerosols and the removal efficiency of aerosolized microorganisms by simple glass microfiber filters. The size distribution of the generated humidity stabilized aerosol particles differed, with 50% relative humidity having a greater number of small diameter particles ( < .02 microns) than aerosols generated at 23% relative humidity, and 23% relative humidity having more particles in the range between .02 and .3 microns than 50%. The removal efficiency of aerosols containing viable bacteria (E. coli) and bacterial viruses (MS2) initially showed greater than 5 logs of removal (99.999%) at both 23% and 50% RHs for both aerosolized microorganisms. Increased RH was related to improved removal of viable aerosolized bacteria and viruses at all timepoints measured over a 60-minute test period. RH had more impact upon removal efficiencies for MS2 bacteriophages than E. coli bacteria, with removal efficiencies for MS2 at 50% RH declining after 30 minutes to levels seen at 23% RH. Some interesting findings of this study were that the two microorganisms that were mixed into a single cocktail at similar concentrations to generate the aerosol apparently did not associate, to a large extent, in the same aerosol particles, as inferred by significant differences in their removal behavior at higher RH of 50%. This study shows that the relative humidity of an aerosol-containing stream should be considered as an important experimental control variable, and that the removal of aerosolized viruses cannot be predicted from bacteria.     

Photo electric nucleus counters for aerosol climatology

Photo electric nucleus counters are used as aerosol detectors at several observatories which are attempting to establish aerosol climatologies. The photo electric nucleus counter has an advantage over absolute nucleus counters in such applications, as it produces a nearly instantaneous “snap shot” of the integrated aerosol concentration in a relatively large volume of air.

The Pollak—Nolan type of photo electric nucleus counter is most frequently used in determining the aerosol concentration at these climatological observatories. Laboratory and field experiments indicate that the response of this instrument is extremely repeatable, even though questions may exist relative to its absolute calibration and the minimum size of particles it detects. The repeatability is sufficiently reliable to permit use of existing data if a more precise calibration is accomplished in the future.

Many components used in construction of replicas of the Pollak—Nolan counter have become difficult to obtain. A transfer of Pollak's calibration to a geometric replica of this instrument, using more modern components would insure continuance of high quality climatic aerosol data.     

Online Nanoparticle Mass Measurement by Combined Aerosol Particle Mass Analyzer and Differential Mobility Analyzer: Comparison of Theory and Measurements

A combination of a differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM) is used to measure the mass of NIST Standard Reference Materials (SRM®) PSL spheres with 60 and 100 nm nominal diameter, and NIST traceable 300 nm PSL spheres. The calibration PSL spheres were previously characterized by modal diameter and spread in particle size. We used the DMA to separate the particles with modal diameter in a narrow mobility diameter range. The mass of the separated particles is measured using the APM. The measured mass is converted to diameter using a specific density of 1.05. We found that there was good agreement between our measurements and calibration modal diameter. The measured average modal diameters are 59.23 and 101.2 nm for nominal diameters of 60 and 100 nm (calibration modal diameter: 60.39 and 100.7 nm) PSL spheres, respectively. The repeatability uncertainty of these measurements is reported. For 300 nm, the measured diameter was 305.5 nm, which is an agreement with calibration diameter within 1.8%.

The effect of spread in particle size on the APM transfer function is investigated. Two sources of the spread in “mono-dispersed” particle size distributions are discussed: (a) spread due to the triangular DMA transfer function, and (b) spread in the calibration particle size. The APM response function is calculated numerically with parabolic flow through the APM and diffusion broadening. As expected from theory, the calculated APM response function and measured data followed a similar trend with respect to APM voltage. However, the theoretical APM transfer function is narrower than the measured APM response.     

Generation of Submicron Arizona Test Dust Aerosol: Chemical and Hygroscopic Properties

This article describes a submicron dust aerosol generation system based on a commercially available dust disperser intended for use in laboratory studies of heterogeneous gas–aerosol interactions. Mineral dust particles are resuspended from Arizona Test Dust (ATD) powder as a case study. The system output in terms of number and surface area is adjustable and stable enough for aerosol flow reactor studies. Particles produced are in the 30–1000 nm size range with a lognormal shape of the number size distribution. The particles are characterized with respect to morphology, electrical properties, hygroscopic properties, and chemical composition. Submicron particle elemental composition is found to be similar for the particle surface and bulk as revealed by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. A significant difference in chemical composition is found between the submicron aerosol and the ATD bulk powder from which it was generated. The anionic composition of the water-soluble fraction of this dust sample is dominated by sulfate. Resuspended dust particles show, as expected, nonhygroscopic behavior in a humid environment. Small hygroscopic growth of about 1% (relative change in mobility diameter) was observed for 100 nm particles when the relative humidity (RH) was changed from 12 to 94%. Particles larger than 100–200 nm shrank about 1% once exposed to RH > 90%. This was interpreted as a restructuring of the larger agglomerates of dust to particles of smaller mobility diameter, under the influence of water vapor.     

The ratio of the extinction coefficient to the mass of atmospheric aerosol particles as a function of the relative humidity

The ratio R_K of the extinction coefficient of aerosol particles in cm ¹, at the wavelength of light λ = 0·55 μm, and the mass of atmospheric aerosol particles in gem³ has been computed as function of the relative humidity for six types of continental and maritime aerosols. With the mean value R_K = 10⁴ cm²/g for all aerosol types being assumed to be independent of relative humidity, only the order of magnitude of the aerosol mass can be determined from visibility observation or measurement of the extinction coefficient of the aerosol particles.     

Determination of the ratio of diffusion charging-based surface area to geometric surface area for spherical particles in the size range of 100–900 nm

Diffusion charging-based surface area for spherical particles was measured and compared with geometric surface area in the submicrometer size ranging from 100 to 900 nm. Spherical aerosol particles (polystyrene latex particles (PSL) and droplets of diethylhexyl sebacate (DEHS)) were generated by electrosprays for 100–600 nm particles and by a condensation generator for 700–900 nm particles. Two commercially available diffusion chargers (DCs) (DC2000CE, Ecochem, USA; LQ1-DC, Matter Engineering, Switzerland) were challenged with monodisperse uncharged spherical aerosols. Results showed that the surface areas measured by the two DCs were proportional to mobility diameter to power 1.22 and 1.38, respectively, in the size range from 100 to 900 nm. Comparison of the DC-based surface area with theoretical active surface area resulted in reasonable agreement within ±30%, indicating that the DCs underestimate geometric surface area of particles. The deviation of the DC-based surface area from the geometric surface area was quantitatively measured and was found to be up to 94% in the size range studied. Three types of aerosol particles were used to validate the correction of the DC deviation from the geometric surface area for particles larger than 100 nm based on the fit obtained for spherical particles in this study: spherical silver particles, carbon nanofibers, and titanium dioxide agglomerates. Comparison of the corrected DC-based surface area to Brunauer–Emmett–Teller (BET)-measured surface area indicated that the DC surface area reasonably agrees with the BET value for the particles tested except carbon nanofibers with 300 nm modal diameter.     

A multi-channel electrical mobility spectrometer with wedge geometry—Design and first evaluation

This paper presents a new design for a multi-channel electrical mobility spectrometer which measures the lognormal size distribution and number concentration of aerosol particles in the size range 5–300 nm with a short response time. The spectrometer charges particles in the test sample by unipolar corona discharge, they are then classified into 16 channels by electrical mobility. Charged particles are detected in the channels by individual aerosol electrometers, giving an electrical mobility spectrum for the sample.The main aspect of the spectrometer design is a wedge-shaped classifier with flat electrodes. This allows a flow to be drawn from the classifier at 16 different levels/channels with minimal disturbance to the remaining flow, hence filter based aerosol electrometers can be used for detection. The varying field within the classifier caused by the wedge shape is advantageous to the classification and optimised through the selection of the wedge angle.Also presented is an alternative technique for inferring the lognormal size distribution of an aerosol from a measured electrical mobility spectrum. This involves using a theoretical model of the instrument to simulate the output mobility spectra for a large number of aerosol samples with lognormal size distributions. The resulting data library can be searched against a measured electrical mobility spectrum to find the corresponding size distribution.The experimental work presented in this paper is a first evaluation of this spectrometer and includes measurement of the classifier transfer functions, basic calibration of the charger, and finally testing the spectrometer's performance on some simple unimodal lognormal aerosol samples.     

Hygroscopic Behavior of Aerosol Particles Emitted from Biomass Fired Grate Boilers

This study focuses on the hygroscopic properties of submicrometer aerosol particles emitted from two small-scale district heating combustion plants (1 and 1.5 MW) burning two types of biomass fuels (moist forest residue and pellets). The hygroscopic particle diameter growth factor (Gf) was measured when taken from a dehydrated to a humidified state for particle diameters between 30–350 nm (dry size) using a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA). Particles of a certain dry size all showed similar diameter growth and the Gf at RH = 90% for 110/100 nm particles was 1.68 in the 1 MW boiler, and 1.5 in the 1.5 MW boiler. These growth factors are considerably higher in comparison to other combustion aerosol particles such as diesel exhaust, and are the result of the efficient combustion and the high concentration of alkali species in the fuel. The observed water uptake could be explained using the Zdanovski-Stokes-Robinson (ZSR) mixing rule and a chemical composition of potassium salts only, taken from ion chromatography analysis of filter and impactor samples (KCl, K₂SO₄, and K₂CO₃). Agglomerated particles collapsed and became more spherical when initially exposed to a moderately high relative humidity. When diluted with hot particle-free air, the fractal-like structures remained intact until humidified in the H-TDMA. A method to estimate the fractal dimension of the agglomerated combustion aerosol and to convert the measured mobility diameter hygroscopic growth to the more useful property volume diameter growth is presented. The fractal dimension was estimated to be ～ 2.5.     

Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated as a means for quantitative analysis of the size, mass, and composition of individual micron-to submicron-sized aerosol particles over a range of well-characterized experimental conditions. Conditional data analysis was used to identify LIBS spectra that correspond to discrete aerosol particles under low aerosol particle loadings. The size distributions of monodisperse particle source flows were measured using the LIBS technique for calcium- and magnesium-based aerosols. The resulting size distributions were in good agreement with independently measured size distribution data. A lower size detection limit of 175 nm was determined for the calcium- and magnesium-based particles, which corresponds to a detectable mass of approximately 3 femtograms. In addition, the accuracy of the LIBS technique for the interference-free analysis of different particle types was verified using a binary aerosol system of calcium-based and chromium particles.     

Relationship Between Biologically Fluorescent Aerosol and Local Meteorological Conditions

Time-resolved characterization of biological aerosol is important both for understanding environmental processes that affect biological aerosols and for determining realistic test conditions for the evaluation of bioaerosol detection systems. Very little work has been done to develop an understanding of the temporal fluctuations in bioaerosol concentration. During an experiment from 1–10 November 2008 ambient biological aerosol and meteorological data were collected. A FLIR/ICx/S3I Instantaneous Bioaerosol Analysis and Collection sensor was used to count both the biological and nonbiological aerosol in two size bins. The data indicate that the ambient relative humidity affects the optically observable concentration of biological aerosol with higher relative humidity generally associated with higher biological aerosol concentrations. The short timescale over which these correlations exist implies an aerosol process, rather than a change in aerosol source.

© 2013 American Association for Aerosol Research     

Effect of Selected Binary and Mixed Solutions on Steam Condensation and Aerosol Behavior in Containment

In the course of severe light water reactor (LWR) core melt accidents, the formation and presence of water soluble compounds will affect the behavior of fission products in the primary system and in the containment. A liquid aerosol mixed with an insoluble component has an affinity to stick on surfaces. A relocation of the deposited aerosol may occur depending on the mole fraction of the solid component and the viscosity of the liquid component in the deposited material. In the very humid conditions expected in the containment, steam will condense on the hygroscopic particles, thereby increasing the size of the particles and settling rate. As a first step in modeling the effects of hygroscopicity, the water activity of a CsOH solution was implemented in the condensation model. The model predicts a significant contribution of CsOH hygroscopicity on the suspended mass concentration, which is in accordance with the observations from the latest large-scale containment aerosol experiments. Results of this simplified CsOH hygroscopicity model were compared with aerosol particles consisting of mixed solutions (e.g., CsOH—Cs₂CO₃—CsI—H₂O) expected in particles released during severe accidents. Water activities of binary and mixed solutions were first calculated using semiempirical methods and these results were compared with the available experimental data. Secondly, different heat and mass transfer models were compared to find a suitable method for the growth rate calculations of hygroscopic aerosol particles. We can conclude that sedimentation of hygroscopic aerosols is an effective removal mechanism for airborne fission products at a high relative humidity in the LWR containment during severe core melt accidents.     

Influence of surfactants on growth of individual aqueous coarse mode aerosol particles

Understanding the links between aerosol and cloud and radiative properties remains a large uncertainty in predicting Earth's changing energy budget. Surfactants are observed in ambient atmospheric aerosol particles, and their effect on cloud droplet growth is a mechanism that was, until recently, neglected in model calculations of particle activation and droplet growth. In this study, coarse mode aqueous aerosol particles were created containing the surfactant Igepal CA-630 and NaCl. The evaporation and condensation of these individual aqueous particles were investigated using an aerosol optical trap combined with Raman spectroscopy. For a relative humidity (RH) change from 70% to 80%, droplets containing both Igepal and NaCl at atmospheric concentrations exhibited on average more than 4% larger changes in droplet radii, compared to droplets containing NaCl only. This indicates enhanced water uptake in the presence of surfactants, but this result is unexpected based on the standard calculation of the effect of surfactants, using surface tension reduction and/or hygroscopicity changes, for particles of this size. One implication of these results is that in periods with increasing RH, surfactant-containing aqueous particles may grow larger than similarly sized aqueous NaCl particles without surfactants, thus shifting atmospheric particle size distributions, influencing particle growth, and affecting aerosol loading, visibility, and radiative forcing.

Copyright © 2018 American Association for Aerosol Research     

PELTI: Measuring the Passing Efficiency of an Airborne Low Turbulence Aerosol Inlet

In an effort to improve the accuracy of airborne aerosol studies, we compared a new porous-diffuser low-turbulence inlet (LTI) with three other inlets on the NSF/NCAR C-130, using both dust and sea salt as test aerosols. Analysis of bulk filters behind the LTI and an external reference total aerosol sampler (TAS) found no significant differences, while both the NASA shrouded solid diffuser inlet (SD) and NCAR community aerosol inlet (CAI) passed smaller amounts. However, scanning electron microscopic analyses of particles behind the LTI and TAS confirmed the model prediction that the LTI porous diffuser (PD) enhanced 7 μm particle concentrations by about 60%. Aerodynamic particle size distributions behind the other inlets began to diverge from enhancement-corrected LTI values above 2 μm, with mass concentrations of larger particles lower by as much as a factor of ten behind the CAI and a factor of 2 behind the SD. We conclude that the corrected LTI distributions were closer to ambient values than those from either the CAI or the SD. Since tubing losses contributed the most uncertainty when deducing ambient supermicron size distributions from LTI data, minimizing them should be a high priority for future experiments. Measured transfer tubing losses were larger than model estimates, in part because of some complex pieces for which no suitable model exists. The LTI represents a significant advance in our ability to sample populations of large particles from aircraft. A necessary part of using an LTI is the calculation of and correction for large-particle enhancement using a computational fluid dynamics (CFD) program. Although the solid diffuser inlet performed well under some conditions, its large-particle efficiency cannot be modeled, varies with humidity and particle morphology, and involves wall contact that has the potential to modify some particles.     

Response Characteristics of PMP Compliant Condensation Particle Counters Toward Various Calibration Aerosols

Within the European legislation, a new limit for particle emissions of light and heavy duty engines based on the particle number (PN) was established in 2011. For PN determination, solid exhaust particles are quantified by means of a condensation particle counter (CPC). In literature, deviations in PN of up to 30% are reported for a comparison of different measurement set-ups. Among others variations in the counting efficiency (CE) of different CPCs have to be considered as possible error sources that contribute to the overall deviation in PN. Thereby the uncertainties in CE may result from variations in the calibration procedure of different manufacturers (e.g., calibration aerosol). To investigate this circumstance, devices from three different manufacturers were directly compared according to their CE for model aerosols. The subject CPCs exhibited differences of up to 17% (23 nm particles) in the counting efficiency when measuring simultaneously the same test aerosol. Depending on the PN size distribution in real exhaust, this might result in an error (～9%) in the finally determined PN. Additionally, the CPC response for selected volatile exhaust components was investigated. In this way, we found out that the fraction of detected nucleation mode particles increases approximately by factor 3 in case particles consist of or contain volatile material (e.g., sulfuric acid).

Copyright 2015 American Association for Aerosol Research