Fine Particle Number Concentrations Research Articles

Ultrafine and Fine Particle Number and Surface Area Concentrations and Daily Cause-Specific Mortality in the Ruhr Area, Germany, 2009-2014.

Background:Although epidemiologic studies have shown associations between particle mass and daily mortality, evidence on other particle metrics is weak.Objectives:We investigated associations of size-specific particle number concentration (PNC) and lung-deposited particle surface area concentration (PSC) with cause-specific daily mortality in contrast to .Methods:We used time-series data (March 2009–December 2014) on daily natural, cardiovascular, and respiratory mortality (NM, CVM, RM) of three adjacent cities in the Ruhr Area, Germany. Size-specific PNC (electric mobility diameter of ), PSC, and were measured at an urban background monitoring site. In single- and multipollutant Poisson regression models, we estimated percentage change (95% confidence interval) [% (95% CI)] in mortality per interquartile range (IQR) in exposure at single-day (0–7) and aggregated lags (0–1, 2–3, 4–7), accounting for time trend, temperature, humidity, day of week, holidays, period of seasonal population decrease, and influenza.Results: and PSC were highly correlated and had similar immediate (lag0–1) and delayed (lag4–7) associations with NM and CVM, for example, 1.12% (95% CI: 0.09, 2.33) and 1.56% (95% CI: 0.22, 2.92) higher NM with IQR increases in at lag0–1 and lag4–7, respectfully, which were slightly stronger then associations with IQR increases in . Positive associations between PNC and NM were strongest for accumulation mode particles (PNC ), and for larger UFPs (PNC ). Associations between NM and changed little after adjustment for or , but were more sensitive to adjustment for .Conclusion:Size-specific PNC () and lung-deposited PSC were associated with natural and cardiovascular mortality in the Ruhr Area. Although associations were similar to those estimated for an IQR increase in , particle number size distributions can be linked to emission sources, and thus may be more informative for potential public health interventions. Moreover, PSC could be used as an alternative metric that integrates particle size distribution as well as deposition efficiency. https://doi.org/10.1289/EHP2054

Highly resolved spatiotemporal variability of fine particle number concentrations in an urban neighborhood

Many research efforts are dedicated to study the high spatiotemporal variability of fine and ultrafine particle concentrations in the urban environment, due to reported associations between exposure to fine particles and plethora of health outcomes. To study the inner-neighborhood variability of such particles, we measured the number concentration of fine particles for six months in five locations across an urban residential neighborhood, using a network of compact optical particles counters. This setup enabled us to apply a wavelet analysis to study the variability of the particle number concentration at different time-scales. Analysis of the particle number concentration (PNC) time series revealed common patterns that could be attributed to regional background PNC, and to neighborhood-scale processes with typical time-scales >4h. Spatially heterogeneous (i.e. local) features in the observed PNC, evident at smaller scales with typical time scales <4h, had no clear long-time pattern. The variability across the neighborhood materialized mainly in the upper percentiles of the PNC distribution rather than in its central measures, revealing a prominent right tail (skewness >1). Wavelet resolved temporal scales of the PNC and wind measurements showed similar spatial patterns, with the correlation between the wavelet coefficients of the two signals mirroring typical temporal and spatial dispersion characteristics at the corresponding scales.

Explaining the spatiotemporal variation of fine particle number concentrations over Beijing and surrounding areas in an air quality model with aerosol microphysics

In this study, a three-dimensional air quality model with detailed aerosol microphysics (NAQPMS + APM) was applied to simulate the fine particle number size distribution and to explain the spatiotemporal variation of fine particle number concentrations in different size ranges over Beijing and surrounding areas in the haze season (Jan 15 to Feb 13 in 2006). Comparison between observations and the simulation indicates that the model is able to reproduce the main features of the particle number size distribution. The high number concentration of total particles, up to 26600 cm−3 in observations and 39800 cm−3 in the simulation, indicates the severity of pollution in Beijing. We find that primary particles with secondary species coating and secondary particles together control the particle number size distribution. Secondary particles dominate particle number concentration in the nucleation mode. Primary and secondary particles together determine the temporal evolution and spatial pattern of particle number concentration in the Aitken mode. Primary particles dominate particle number concentration in the accumulation mode. Over Beijing and surrounding areas, secondary particles contribute at least 80% of particle number concentration in the nucleation mode but only 10–20% in the accumulation mode. Nucleation mode particles and accumulation mode particles are anti-phased with each other. Nucleation or primary emissions alone could not explain the formation of the particle number size distribution in Beijing. Nucleation has larger effects on ultrafine particles while primary particles emissions are efficient in producing large particles in the accumulation mode. Reduction in primary particle emissions does not always lead to a decrease in the number concentration of ultrafine particles. Measures to reduce fine particle pollution in terms of particle number concentration may be different from those addressing particle mass concentration.

Investigation on the relationship between the fine particle emission and crystallization characteristics of gypsum during wet flue gas desulfurization process

The relationship between the fine particles emitted after desulfurization and gypsum crystals in the desulfurization slurry was investigated, and the crystallization characteristics varying with the operation parameters and compositions of the desulfurization slurry were discussed. The results showed that the fine particles generated during the desulfurization process were closely related to the crystal characteristics in the desulfurization slurry by comparison of their morphology and elements. With the higher proportion of fine crystals in the desulfurization slurry, the number concentration of fine particles after desulfurization was increased and their particle sizes were smaller, indicating that the optimization of gypsum crystallization was beneficial for the reduction of the fine particle emission. The lower pH value and an optimal temperature of the desulfurization slurry were beneficial to restrain the generation of fine crystals in the desulfurization slurry. In addition, the higher concentrations of the Fe3+ ions and the F− ions in the desulfurization slurry both promoted the generation of fine crystals with corresponding change of the morphology and the effect of the Fe3+ ions was more obvious. With the application of the desulfurization synergist additive, it was beneficial for the inhibition of fine crystals while the thinner crystals were generated.

Formation and decomposition of NH4HSO4 during selective catalytic reduction of NO with NH3 over V2O5-WO3/TiO2 catalysts

Based on commercial V2O5-WO3/TiO2 catalysts, the formations of ammonium bisulfate (ABS) and ammonium sulfate were detected from the reactions among SO3, NH3 and H2O in the flue gas during the process of selective catalytic reduction (SCR) of NO with NH3, leading to the deactivation of the catalyst and the increased number concentration of fine particles. The mechanism of formation and decomposition of ABS during SCR of NO with NH3 was investigated through the In Situ Diffuse Reflectance Infrared Spectroscopy (DRIFTS) and the Thermo Gravimetric analyzer coupled with Fourier Transform Infrared analyzer (TG-FTIR). The results of the in situ DRIFTS showed that ABS deposited on the surface of the catalysts could be generated from the adsorption activation of NH3 with SO2 in presence of O2. It also could be produced by the direct reaction between NH3 and the intermediate metal sulfates on the surface of the catalysts. In addition, it suggested that the reaction between NO and NH4+ in ABS promoted ABS decomposition. TG-FTIR demonstrated that the process of ABS decomposition on the catalysts was composed of two steps. Moreover, the temperature window of the complete pyrolysis of ABS was delayed by catalysts.

Occupational Exposure to Cobalt and Tungsten in the Swedish Hard Metal Industry: Air Concentrations of Particle Mass, Number, and Surface Area.

Exposure to cobalt in the hard metal industry entails severe adverse health effects, including lung cancer and hard metal fibrosis. The main aim of this study was to determine exposure air concentration levels of cobalt and tungsten for risk assessment and dose–response analysis in our medical investigations in a Swedish hard metal plant. We also present mass-based, particle surface area, and particle number air concentrations from stationary sampling and investigate the possibility of using these data as proxies for exposure measures in our study. Personal exposure full-shift measurements were performed for inhalable and total dust, cobalt, and tungsten, including personal real-time continuous monitoring of dust. Stationary measurements of inhalable and total dust, PM2.5, and PM10 was also performed and cobalt and tungsten levels were determined, as were air concentration of particle number and particle surface area of fine particles. The personal exposure levels of inhalable dust were consistently low (AM 0.15mg m−3, range <0.023–3.0mg m−3) and below the present Swedish occupational exposure limit (OEL) of 10mg m−3. The cobalt levels were low as well (AM 0.0030mg m−3, range 0.000028–0.056mg m−3) and only 6% of the samples exceeded the Swedish OEL of 0.02mg m−3. For continuous personal monitoring of dust exposure, the peaks ranged from 0.001 to 83mg m−3 by work task. Stationary measurements showed lower average levels both for inhalable and total dust and cobalt. The particle number concentration of fine particles (AM 3000 p·cm−3) showed the highest levels at the departments of powder production, pressing and storage, and for the particle surface area concentrations (AM 7.6 µm2·cm−3) similar results were found. Correlating cobalt mass-based exposure measurements to cobalt stationary mass-based, particle area, and particle number concentrations by rank and department showed significant correlations for all measures except for particle number. Linear regression analysis of the same data showed statistically significant regression coefficients only for the mass-based aerosol measures. Similar results were seen for rank correlation in the stationary rig, and linear regression analysis implied significant correlation for mass-based and particle surface area measures. The mass-based air concentration levels of cobalt and tungsten in the hard metal plant in our study were low compared to Swedish OELs. Particle number and particle surface area concentrations were in the same order of magnitude as for other industrial settings. Regression analysis implied the use of stationary determined mass-based and particle surface area aerosol concentration as proxies for various exposure measures in our study.

Crystallisation of tricalcium aluminate from sodium aluminate solution using slaked lime

Crystallisation of tricalcium aluminate (TCA) hydrate was investigated by reacting slaked lime with sodium aluminate solution at 368K in an agitated baffled batch and continuous reactors. Using an x-ray diffraction calibration established by the intensity ratio of characteristic peaks of lime-TCA admixtures; it was determined that >90% of the slaked lime was converted to TCA within 5min in the batch reactor. From particle counting measurements, TCA nucleation and growth was observed within the first 30s by an increase in 2–5μm particles, whereas finer particle counts decreased due to lime dissolution. The mean particle size based on particle counting increased up to 10μm due to growth dominated by agglomeration of sub-particles over the course of 2h. The TCA particle morphology initiated as hexagonal platelets which became arranged as “rosettes” then filled in to become spherical. Reaction seeding with 10wt.% of the total final solid TCA mass resulted in a narrower particle size distribution. Seed loading did not significantly influence the particle morphology, however slight growth of TCA sub particles was evident from the micrographs. The effect of the key operating parameters, residence time and agitation intensity, were then assessed in the context of Bayer liquor filter aid production in an agitated continuous reactor. As the residence time was increased, the fine particle number concentration decreased and particle growth increased which was dominated by agglomeration. With a longer residence times, the particles become highly agglomerated leaving little void space which is undesirable in terms of filter aid quality. An agitation intensity of 600RPM which exerts a maximum Reynolds number of 9200 on the fluid phase based on tip speed and residence time of 30min generated the best filter aid in terms of minimising the fine particle fraction and minimising large agglomerates.

Oil Sorbents based on Methacrylic Acid - Grafted Polypropylene Fibers: Synthesis and Characterization

People are exposed to polycyclic aromatic hydrocarbons (PAHs) outdoors and indoors. Although there is a fair amount of literature review concerning exposure to settled dust, and in particular, to PAHs indoors, no attempts have been made to report contamination in household settled floor dust in Jordan. In this study we aimed at identifying the source origin of the PAHs as indoors or outdoors inside eight selected dwellings in Amman, Jordan. We also aimed at investigating the spatial variation of the analyzed PAHs concentrations within Amman. The floor dust samples were collected from the entrance and living room areas. The total PAHs concentrations at the living room area ranged from 65422 ng/g to about 641 ng/g. At the entrance area, the highest total PAHs concentration was about 9266 ng/g and the lowest was about 241 ng/g. The differences among dwellings for the total and individual PAHs concentrations confirms that each dwelling has its own environmental conditions and we cannot make a general conclusion with respect to the source origin as indoors or outdoors. The spatial variation of the PAHs concentrations showed that the north-eastern part of Amman had lower PAHs concentrations than that observed in the south-western part. This agrees well with a previous study about the spatial variation of fine aerosol particle number concentrations measured within the city during the same period by Hussein et al. who reported that fine particle number concentrations in the north eastern part of the city is lower than that in the south western part.

Using a Mobile Measurement to Characterize Number, Surface Area, and Mass Concentrations of Ambient Fine Particles with Spatial Variability during and after a PM Episode

Fine particles play a key role in regional air quality deterioration. Commonly used central-site monitoring data, which offer rough determinations of spatial particulate matter (PM) distributions, is insufficient to estimate potential local emissions or population exposure levels. This study characterizes the spatial variability of fine particles in suburban and rural regions during and after a winter episode of elevated PM (PM episode). Commercial instruments of high time resolution in a mobile laboratory platform were deployed to measure the distribution, number, surface area, and mass concentrations of fine particles. Spatial variations of those particle properties were mainly affected by regional feature, PM episode, local primary source and wind speed. Particle concentrations and size distributions were found to differ considerably during and after PM episode. The PM episode was found to exhibit a lower degree of spatial concentration contrast with respect to particle number, surface area and mass, where similar particle size patterns were distributed across all study regions with decreased particle number under nucleation and Aitken modes and increased number under the accumulation mode. The mobile measurement may supplement information on spatial particle distributions for estimating levels of population exposure and for characterizing detailed physical properties of short-term, high-exposed scenarios.

Source appointment of fine particle number and volume concentration during severe haze pollution in Beijing in January 2013.

Extreme haze episodes repeatedly shrouded Beijing during the winter of 2012-2013, causing major environmental and health problems. To better understand these extreme events, particle number size distribution (PNSD) and particle chemical composition (PCC) data collected in an intensive winter campaign in an urban site of Beijing were used to investigate the sources of ambient fine particles. Positive matrix factorization (PMF) analysis resolved a total of eight factors: two traffic factors, combustion factors, secondary aerosol, two accumulation mode aerosol factors, road dust, and long-range transported (LRT) dust. Traffic emissions (54%) and combustion aerosol (27%) were found to be the most important sources for particle number concentration, whereas combustion aerosol (33%) and accumulation mode aerosol (37%) dominated particle volume concentrations. Chemical compositions and sources of fine particles changed dynamically in the haze episodes. An enhanced role of secondary inorganic species was observed in the formation of haze pollution. Regional transport played an important role for high particles, contribution of which was on average up to 24-49% during the haze episodes. Secondary aerosols from urban background presented the largest contributions (45%) for the rapid increase of fine particles in the severest haze episode. In addition, the invasion of LRT dust aerosols further elevated the fine particles during the extreme haze episode. Our results showed a clear impact of regional transport on the local air pollution, suggesting the importance of regional-scale emission control measures in the local air quality management of Beijing.

Origin of high particle number concentrations reaching the St. Louis, Midwest Supersite

Ultrafine particles are associated with adverse health effects. Total Particle Number Concentration (TNC) of fine particles were measured during 2002 at the St. Louis — Midwest supersite. The time series showed overall low level with frequent large peaks. The time series was analyzed alongside criteria pollutant measurements and meteorological observations. Multiple regression analysis was used to identify further contributing factors and to determine the association of different pollutants with TNC levels. This showed the strong contribution of sulfur dioxide (SO2) and nitrogen oxides (NOx) to high TNC levels. The analysis also suggested that increased dispersion resulting from faster winds and higher mixing heights led to higher TNC levels. Overall, the results show that there were intense particle nucleation events in a SO2 rich plume reaching the site which contributed around 29% of TNC. A further 40% was associated with primary emissions from mobile sources. By separating the remaining TNC by time of day and clear sky conditions, we suggest that most likely 8% of TNC are due to regional nucleation events and 23% are associated with the general urban background.

Source apportionment of urban fine particle number concentration during summertime in Beijing

Continuous particle number size distributions (15 nm–2.5 μm), particle chemical compositions, gaseous species and meteorological variables were collected at an urban site in Beijing to investigate the source apportionment of ambient fine particle number concentrations. Hourly data sets were analyzed using the positive matrix factorisation (PMF) which identified a total of eight factors: two traffic factors, two combustion factors, secondary nitrate factors, secondary sulfate + secondary organic aerosol (SOA), fugitive dust and regionally transported aerosol. Traffic (47.9%) and combustion (29.7%) aerosol were found to dominate the particle number concentrations, whereas the most important sources for particle volume concentrations were found to be regionally transported aerosol (30.9%) and combustions (30.1%). Although the diurnal pattern of each of the two traffic factors closely followed traffic rush hour for Beijing, their size modes were different suggesting that these factors might represent local and remote emissions. Biomass burning and coal-fired power plant aerosol were distinguished according to their size modes and chemical species associated with them. Secondary compounds showed similar bimodal particle number size distribution, the distinct diurnal pattern distinguished these factors as secondary nitrate and mixed source of secondary sulfate and SOA. Regionally transported material was characterized by accumulation mode particles. Overall, the introduction of combinations of particle number size distributions and chemical composition data in PMF model is successful at separating the components and quantifying relative contributions to the particle number and volume size distributions in the complex urban atmosphere.

Near-Surface Vertical Profiles of Urban Roadside NOx and Fine Particles

This paper presents daytime vertical profiles of the NOx concentration, and the number concentration and size distribution of fine particles near a major road in urban Tokyo during spring 2011. No significant height dependence was observed in the NOx concentration, presumably due to rapid diffusion. In contrast, the number concentration of particles under 0.5 µm diameter demonstrated an exponential decrease with increasing height above ground level. Vertical profiles derived from this study differ from those presented in previous studies, however, these differences may potentially be explained by the different tailpipe positions of Japanese and US heavy vehicles, as well as the meteorological conditions. This study demonstrates that in Tokyo, the fine particle concentration at 0.5 m above ground level was about 2.9 times higher than that at 2.0 m. The higher fine particle concentration immediately above ground level implies that children may be at greater risk of experiencing pollutant-related respiratory symptoms than adults.

Air conditioning impact on the dynamics of radon and its daughters concentration

Radon and its decay products are harmful pollutants present in indoor air and are responsible for the majority of the effective dose due to ionising radiation that people are naturally exposed to. The paper presents the results of the series of measurements of radon and its progeny (in unattached and attached fractions) as well as indoor air parameters: temperature, relative humidity, number and mass concentrations of fine aerosol particles. The measurements were carried out in the auditorium (lecture hall), which is an indoor air quality laboratory, in controlled conditions during two periods of time: when air conditioning (AC)was switched off (unoccupied auditorium) and when it was switched on (auditorium in normal use). The significant influence of AC and of students' presence on the dynamics of radon and its progeny was confirmed. A decrease in the mean value of radon and its attached progeny was found when AC was working. The mean value of radon equilibrium factor F was also lower when AC was working (0.49) than when it was off (0.61). The linear correlations were found between attached radon progeny concentration and particle number and mass concentration only when the AC was switched off. This research is being conducted with the aim to study the variability of radon equilibrium factor F which is essential to determine the effective dose due to radon and its progeny inhalation.

Measurement of particle number and related pollutant concentrations in an urban area in South Brazil

The purpose of the present study was to analyze atmospheric particle number concentration at Sapucaia do Sul, in the Metropolitan Area of Porto Alegre, and associate it with the pollutants NO, NO2, and O3. Measurements were performed in two periods: August to October, in 2010 and 2011. We used the following equipment: the continuous particulate monitor (CPM), the chemiluminescent nitrogen oxide analyzer (AC32M), and the UV photometric ozone analyzer (O342M). Daily and hourly particle number concentrations in fractions PR1.0 (0.3–1.0 μm), PR2.5 (1.0–2.5 μm), and PR10 (2.5–10 μm), and concentrations of pollutants NO, NO2, NOx, and O3 were measured. These data were correlated with meteorological parameters such as wind speed, temperature, relative humidity, and solar radiation. The daily variation of OX (NO2 + O3) and its relation with NO2 were also established. The results obtained for daily particle number concentration (particles L−1) showed that the area of study had higher particle number of PR2.5 and PR1.0 size ranges, with values of 19.5 and 28.51 particles L−1, respectively. Differences in particle number concentrations in PR1 and PR2.5 size ranges were found between weekdays and weekends. The daily variation per hour of concentrations of particle number, NO, and NOx showed peaks during increased traffic flow in the morning and in the evening. NO2 showed peaks at different times, with the first peak (morning) 2 h after the peak of NO, and a second peak in the evening (19:00). This is due to the oxidation of NO and to the photolysis of NO3 formed overnight. Correlation analysis suggests that there may be a relationship between the fine and ultrafine particles and NO, probably indicating that they have similar sources, such as vehicular emissions. In addition, a possible relationship of solar radiation with fine particle number concentrations, as well as with O3 was also observed. The results, too, show an inverse relationship between particle number concentration and relative humidity.

A new algorithm to solve condensation/evaporation for ultra fine, fine, and coarse particles

A new algorithm for condensation/evaporation has been developed that is accurate for both mass and number concentrations over the full size range of ultra fine, fine, and coarse particles. This new algorithm is compared to several standard sectional and modal algorithms for two case studies. In this algorithm, we use the Euler scheme for the number concentration of ultra fine particles and the Euler scheme for the mass concentration of fine and coarse particles. The results of this study provide useful information to select algorithms in order to correctly simulate aerosol dynamics in air quality models over a wide range of particle sizes.

Size distribution of atmospheric aerosols at Maitri, Antarctica

Abstract Measurements of the concentration and size distribution of the atmospheric aerosol particles in the size range of 0.003–20 μm diameter have been made at Maitri (70°45′52″S, 11°44′03″E) during January–February, 2005. The measured particle size ranges extended from 0.5 to 20 μm throughout the period, from 0.016 to 0.7 μm in January and 0.01 to 0.4 μm in February. For short intervals of time, comprising a total period of 210 h, the measurements were made for particles in the size range of 0.003–0.16 μm. Total particle number concentrations of coarse and fine particles vary from 0.1 to 0.8 and from 100 to 2000 particles cm −3 , respectively. The fine particle concentration undergoes a diurnal variation with values remaining low (300–400 cm −3 ) during low sun periods and increasing up to ∼750 cm −3 at noontime. The monthly-averaged number size distributions show maxima in accumulation mode at 0.772 ± 0.023 μm, in Aitken mode at 0.089 ± 0.005 μm in January which shifts to 0.03 ± 0.003 μm in February, and in nucleation mode at 0.018 ± 0.002 μm. The hourly-averaged curves can have one mode each in coarse, accumulation, and nucleation size ranges, and two modes in Aitken size range of particles. Total number concentration of particles in coarse mode is higher in oceanic than in continental air masses. Further, while the oceanic air masses have nucleation mode at 0.01 μm and Aitken mode at 0.024 μm, continental air masses have nucleation mode at 0.017 μm. Intermixing of the two air masses at coastal site results in multi-modal size distributions. It is inferred that while in continental air masses the nucleation mode particles are aged, in oceanic air masses these are likely to be transported from the upper troposphere under subsidence of cyclonic storms revolving around the continent of Antarctica.

Seasonal variations and vertical features of aerosol particles in the Antarctic troposphere

Abstract. Tethered balloon-borne aerosol measurements were conducted at Syowa Station, Antarctica during the 46th Japanese Antarctic expedition (2005–2006). The CN concentration reached a maximum in the summer, although the number concentrations of fine particles (Dp&gt;0.3 μm) and coarse particles (Dp&gt;2.0 μm) increased during the winter–spring. The CN concentration was 30–2200 cm−3 near the surface (surface – 500 m) and 7–7250 cm−3 in the lower free troposphere (&gt;1500 m). During the austral summer, higher CN concentration was often observed in the lower free troposphere, where the number concentrations in fine and coarse modes were remarkably lower. The frequent appearance of higher CN concentrations in the free troposphere relative to continuous aerosol measurements at the ground strongly suggests that new particle formation is more likely to occur in the lower free troposphere in Antarctic regions. Seasonal variations of size distribution of fine-coarse particles show that the contribution of the coarse mode was greater in the winter–spring than in summer because of the dominance of sea-salt particles in the winter–spring. The number concentrations of fine and coarse particles were high in air masses from the ocean and mid-latitudes. Particularly, aerosol enhancement was observed not only in the boundary layer, but also in the lower free troposphere during and immediately after Antarctic haze events occurring in May, July and September.

Exposure to fine particle mass and number concentrations in urban transportation environments of New York City

Travelers’ real-time exposure to fine particles is assessed in terms of particle mass and number concentrations across various transportation-related micro-environments in New York City. Substantial spatial/temporal variations were observed in both the mass and number metrics of fine particles. Comparisons of exposure levels to fine particles across location categories reveals significant differences between particle mass and number concentration measurements; while the highest particle number concentration is on urban street sides, subway trains, with the lowest fine particle number concentration, has the second highest mass. Statistical analysis confirms this disparity.

Use of a Condensation Particle Counter and an Optical Particle Counter to Assess the Number Concentration of Engineered Nanoparticles

There is a need to evaluate nanoparticle (< 100 nm) exposures in occupational settings. However, portable instruments do not size segregate particles in that size range. A proxy method for determining nanoparticle count concentrations involves subtracting counts made with a condensation particle counter (CPC) from those of an optical particle counter/sizer (OPC), resulting in an estimation of “very fine” particles < 300 nm, where 300 nm is the OPC lower detection limit. However, to determine size distributions from which particles < 100 nm may be estimated, the resulting count of particles < 300 nm can be used as an additional channel of count data in addition to those obtained from the OPC. To test these methods, the very fine number concentrations determined using a CPC and OPC were compared with those from SMPS measurements and were used to verify the accuracy of a very fine particle number concentration determined by an OPC and CPC. Two “size-distribution” methods, weighted-average and log-probit, were applied to reproduce particle size distributions from OPC and CPC data and were then evaluated relative to their ability to accurately estimate the nanoparticle number concentrations. Various engineered nanoparticles were used to create test aerosols, including titanium dioxide (TiO 2 ), silicon dioxide (SiO 2 ), and iron oxide (Fe 2 O 3 ). These materials were chosen because of their different refractive indices and therefore may be measured differently by the OPC. The count-difference method was able to estimate very fine particle number concentrations with an error between 10.9 to 58.4%. In estimating nanoparticle number concentrations using the size-distribution methods, the log-probit method resulted in the lowest percent errors that ranged from –42% to 1023%. Percent error was lower than the instrument manufacturer's indicated level of accuracy when the test aerosol refractive index was similar to that used for OPC calibration standards. Accuracy could be increased if there was an increase in the size resolution for number concentrations measured by the CPC of very fine particles and mitigation of optical effects.