Seongheon Kim

Concentration and size distribution of ultrafine particles near a major highway.

Abstract Motor vehicle emissions usually constitute the most significant source of ultrafine particles (diameter <0.1 μm) in an urban environment, yet little is known about the concentration and size distribution of ultrafine particles in the vicinity of major highways. In the present study, particle number concentration and size distribution in the size range from 6 to 220 nm were measured by a condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS), respectively. Measurements were taken 30, 60, 90, 150, and 300 m downwind, and 300 m upwind, from Interstate 405 at the Los Angeles National Cemetery. At each sampling location, concentrations of CO, black carbon (BC), and particle mass were also measured by a Dasibi CO monitor, an aethalometer, and a DataRam, respectively. The range of average concentration of CO, BC, total particle number, and mass concentration at 30 m was 1.7−2.2 ppm, 3.4−10.0 μg/m3, 1.3−2.0 × 105/cm3, and 30.2−64.6 μ/m3, respectively. For the conditions of these measurements, relative concentrations of CO, BC, and particle number tracked each other well as distance from the freeway increased. Particle number concentration (6–220 nm) decreased exponentially with downwind distance from the freeway. Data showed that both atmospheric dispersion and coagulation contributed to the rapid decrease in particle number concentration and change in particle size distribution with increasing distance from the freeway. Average traffic flow during the sampling periods was 13,900 vehicles/hr. Ninety-three percent of vehicles were gasoline-powered cars or light trucks. The measured number concentration tracked traffic flow well. Thirty meters downwind from the freeway, three distinct ultrafine modes were observed with geometric mean diameters of 13, 27, and 65 nm. The smallest mode, with a peak concentration of 1.6 × 105/cm3, disappeared at distances greater than 90 m from the freeway. Ultrafine particle number concentration measured 300 m downwind from the freeway was indistinguishable from upwind background concentration. These data may be used to estimate exposure to ultrafine particles in the vicinity of major highways.

Use of a stratified oxidative stress model to study the biological effects of ambient concentrated and diesel exhaust particulate matter.

Although several epidemiological studies have shown a positive relationship between exposure to ambient air particulate matter (PM) and adverse health effects in humans, there is still a fundamental lack of understanding of the most toxic particle components and the biological mechanisms through which they act. Since our studies on the biological effects of diesel exhaust particles (DEP) have highlighted the role of reactive oxygen species (ROS), catalyzed by organic chemical compounds, we set out to establish whether this constitutes an oxidative stress model that can be used to study the biological effects of ambient coarse and fine PM. We demonstrate that organic DEP extracts induce a stratified oxidative stress response, leading to heme oxygenase 1 (HO-1) expression at normal GSH/ GSSG ratios, proceed to Jun kinase activation and interleukin 8 (IL-8) production at intermediary oxidative stress levels, and culminate in cellular apoptosis in parallel with a sharp decline in GSH/GSSG ratios. We demonstrate that ambient concentrated air particulates, collected with a particle concentrator and a liquid impinger, mimic the effects of organic DEP extracts at lower oxidative stress levels. While fine PM consistently induced HO-1 expression in all most of the samples collected over a 9-mo survey period, coarse particulates were effective at inducing that effect during fall and winter. Moreover, HO-1 expression was positively correlated to the higher organic carbon (OC) and polyaromatic hydrocarbons (PAHs) content of fine versus coarse PM, as well as the rise in PAH content that occurs in coarse PM during the winter months. Although coarse and fine PM lead to a decrease in cellular glutathione (GSH)/GSSG ratios, oxidative stress did not increase to cytotoxic levels. Taken together, these data demonstrate that it is possible to use the stratified oxidative stress model developed for DEP to interpret the biological effects of coarse and fine PM. This work has important implications for the selection of relevant biological endpoints for in vivo studies.

Size distribution and diurnal and seasonal trends of ultrafine particles in source and receptor sites of the Los Angeles basin.

Abstract This paper presents results from a study conducted in two urban areas of southern California, Downey and Riverside, to examine the effect of different sources and formation mechanisms on the size distribution and temporal trends of ultrafine particles. Near-continuous data were collected for 5 months at each location. Our data clearly identified Downey as a source site, primarily affected by vehicular emissions from nearby freeways, and Riverside as a receptor site, where photochemical secondary reactions form a substantial fraction of particles, along with local vehicular emissions. In Downey, the diurnal trends of total particle number concentration and elemental carbon (EC) appear to be almost identical throughout the day and irrespective of season, thereby corroborating the role of primary emissions in the formation of these particles. This agreement between EC and particle number was not observed in Riverside during the warmer months of the year, while very similar trends to Downey were observed during the winter months in that area. Similarly, the size distribution of ultrafine particles in Downey was generally unimodal with a mode diameter of 30–40 nm and without significant monthly variations. The number-based particle size distributions obtained in Riverside were bimodal, with a significant increase in accumulation mode as the season progressed from winter to summer. During the warmer months, there was also an increase in sub-100-nm particles in the afternoon hours, between 2:00 p.m. and 4:00 p.m., that also increased with the temperature. The differences observed in the ultrafine particle distribution and temporal trends clearly demonstrated that mechanisms other than direct emissions play an important role in the formation of ultrafine particles in receptor sites of the Los Angeles Basin.

Versatile aerosol concentration enrichment system (VACES) for simultaneous in vivo and in vitro evaluation of toxic effects of ultrafine, fine and coarse ambient particles. Part I: Development and laboratory characterization

Abstract This study presents the development and bench-testing of a versatile aerosol concentration enrichment system (VACES) capable of simultaneously concentrating ambient particles of the coarse, fine and ultrafine size fractions for conducting in vivo and in vitro studies. The VACES consists of three parallel sampling lines (concentrators), each operating at an intake flow rate of 110 l min −1 . Coarse particles are concentrated using a single round nozzle virtual impactor. Concentration enrichment of PM2.5 and ultrafine particles is accomplished by first drawing air samples through two parallel lines, having 2.5 and 0. 18 μm cutpoint pre-impactors, respectively, to remove particles larger than these sizes from the air sample. Both of the smaller PM fractions are drawn through a saturation–condensation system that grows particles to 2– 3 μm droplets, which are subsequently concentrated by virtual impaction. A diffusion dryer is used in the fine and ultrafine concentrators to remove excess vapor and return the concentrated particles to their original size, prior to supplying them for in vivo exposures. The VACES can also provide highly concentrated liquid suspensions of particles of these three modes for in vitro toxicity studies. This is accomplished by connecting the concentrated output (minor) flows of each of the VACES parallel concentrators to a liquid impinger (BioSampler), used in a modified configuration, to collect particles under near-ambient pressure. Detailed laboratory characterization of the individual components of the VACES are presented in this paper, including evaluation of its ability to preserve particle mass, number, and chemical species during the concentration enrichment process. Our experimental results showed that concentration enrichment is accomplished with very high efficiency, minimal particle losses and without any significant dependence on particle size or chemical composition.

Versatile aerosol concentration enrichment system (VACES) for simultaneous in vivo and in vitro evaluation of toxic effects of ultrafine, fine and coarse ambient particles Part II: Field evaluation

Abstract This study presents results from a field evaluation of a mobile versatile aerosol concentration enrichment system (VACES), designed to enhance the ambient concentrations of ultrafine (less than 0.18 μm ), fine (0– 2.5 μm ), and coarse particles (2.5– 10 μm ) for in vivo and in vitro toxicity studies. The VACES may be coupled to an exposure chamber system to assess exposure-dose effects of any one, or all, of ambient aerosol on either human subjects and/or animals. Alternatively, concentrated ultrafine, fine and coarse particles can be directly collected by impaction onto a medium suitable for application to cell cultures for in vitro evaluation of their toxic effects. The enrichment and preservation of ambient ultrafine, fine and coarse particles by size and chemical composition was determined by comparisons made between the VACES and a co-located multistage MOUDI impactor, used as a reference sampler. Furthermore, preservation of the ultrafine fraction is measured by the enrichment based on ultrafine particle numbers, morphological characteristics as well as their elemental carbon (EC) content. The results suggest that the concentration enrichment process of the VACES does not differentially affect the particle size or chemical composition of ambient PM. The following fractions: (1) mass (coarse and fine PM); (2) number (ultrafine PM); (3) sulfate (fine PM); (4) nitrate (fine PM, after correcting for nitrate losses within the MOUDI); (5) EC (ultrafine PM); and (6) selected trace elements and metals (coarse and fine PM), are concentrated very close to the “ideal” enrichment value of 22—thereby indicating a near 100% concentration efficiency for the VACES. Furthermore, ultrafine particles are concentrated without substantial changes in their compactness or denseness, as measured by the fractal dimension analysis.

Reduction of nitrate losses from filter and impactor samplers by means of concentration enrichment

Abstract Sampling errors (artifacts) have greatly affected the precision of the quantitative analysis of volatile species, such as particulate ammonium nitrate. This work presents the effect of the enrichment in concentration of particulate nitrate in reducing volatilization losses in impactors and Teflon filter samplers. During the performance characterization of an ambient fine particle concentrator developed by Sioutas et al. (1995a, Environmental Health Perspectives 103, 172–177, 1995b, Inhalation Toxicology, 7, 633–644, 1977, Journal of Aerosol Science 28, 1057–1071) losses of ambient ammonium nitrate from denuded and undenuded Teflon filter samplers as well as the microorifice uniform deposit impactor (MOUDI) were evaluated in Los Angeles, CA, an area where ammonium nitrate constitutes a major component of ambient fine particulate matter. The field study data were compared to those predicted theoretically for a given set of gas and particulate nitrate concentrations, temperature and relative humidity. Both theoretical and experimental results indicated that the ratio of nitrate gas-to-particle concentration affects significantly the volatilization loss, with higher volatilization losses occurring at higher gas-to-particle concentration values. The concentration enrichment of particulate-phase nitrate resulted in reducing evaporation losses from the MOUDI from 20–50% to less than 10%. Losses of nitrate from denuded Teflon filters were reduced from 60–95% to less than 30%, and for undenuded Teflon filters from 30–80% to less than 5%. Our study concluded that nitrate losses from impactor, denuded and undenuded Teflon filter samplers could be virtually eliminated by placing the sampler downstream of a particle concentrator with a small cutpoint (i.e., 0.1xa0μm).

Field evaluation of a modified DataRAM MIE scattering monitor for real-time PM2.5 mass concentration measurements

Abstract In this paper, we investigated the feasibility of using a modified DataRAM nephelometer (RAM-1, MIE Inc., Billerica, MA) as a continuous PM 2.5 monitor to measure concentrations of ambient and concentrated aerosols in real time. The DataRAM operated with a diffusion dryer tube in its inlet in order to reduce the relative humidity of the sampled air to less than 50%. A total of 39 field tests were conducted in which the average dry DataRAM concentration was compared to the gravimetrically determined mass concentration, corrected for nitrate losses. Tests were conducted over one calendar year (from January to December 1999) in order to capture maximum seasonal variations in the levels of relative humidity, PM size distribution and chemical composition in the Los Angeles Basin. Our experimental results indicated that the aerosol mass median diameter (MMD) is the single, most important parameter in affecting the response of the DataRAM. As the MMD increases from 0.3 to 1.1xa0μm, the DataRAM-to-MOUDI ratio increases from approximately 0.7 to about 1.6. The DataRAM-to-MOUDI ratio subsequently decreases to about 1.0, as the MMD further increases to 1.5xa0μm. For MMD values in the range of 0.4–0.7xa0μm (i.e., the MMD size range that is most commonly associated with urban aerosols), the DataRAM and gravimetrically measured mass concentrations (corrected for nitrate losses) agree within ±20%. Based only on ambient data, the average DataRAM-to-gravimetric concentration ratio was 0.93 (±0.17), whereas the average DataRAM-to-gravimetric concentration ratio for concentrated PM 2.5 aerosols was 1.23 (±0.20). Our field evaluation also indicated that the effect of particle chemical composition on the DataRAM-to-gravimetric concentration ratio is much less important than that of particle size distribution.

A Methodology for Measuring Size-Dependent Chemical Composition of Ultrafine Particles

Ultrafine particulate matter (PM) consists of particles mostly emitted by combustion sources but also formed during gas-to-particle formation processes in the atmosphere. Various studies have shown these particles to be toxic. The very small mass of these particles has posed a great challenge in determining their size-dependent chemical composition using conventional aerosol sampling technologies. Implementing 2 technologies in series has made it possible to overcome these 2 problems. The first technology is the USC Ultrafine Concentrator, which concentrates ultrafine particles (i.e., 10-180 nm) by a factor of 20-22. Ultrafine particles are subsequently size fractionated and collected on suitable substrates using the NanoMOUDI, a recently developed cascade impactor that classifies particles in 5 size ranges from 10 to 180 nm. The entire system (concentrator + NanoMOUDI) was employed in the field at 2 different locations in the Los Angeles Basin in order to collect ultrafine particles in 3 consecutive 3 h time intervals (i.e., morning, midday, and afternoon). The results indicate a distinct mode in the 32-56 nm size range that is most pronounced in the morning and decreases throughout the day at Downey, CA (a source site), affected primarily by vehicular PM emissions. While the mass concentrations at the source site decrease with time, the levels measured at Riverside, CA (a receptor site), are highest in the afternoon with a minimum at midday. In Riverside, ultrafine EC (elemental carbon) and OC (organic carbon) concentrations were highly correlated only during the morning period, whereas these correlations collapsed later in the day. These results indicate that in this area, ultrafine PM is generated by primary emissions during the morning hours, whereas secondary aerosol formation processes become more important as the day progresses.

A high flow rate, very low pressure drop impactor for inertial separation of ultrafine from accumulation mode particles

Abstract This paper presents the development and evaluation of a high-volume, multiple rectangular (slit) geometry jet impactor. Operating with a preselective inlet that removes particles larger than 2.5 μm in aerodynamic size, the impactor has been designed to separate ultrafine ( μm ) from the accumulation mode range ( 0.15 p μm ). Particles are accelerated by passing through 10 parallel slits nozzles, each 12.5 cm long by 0.0125 cm wide. The average jet velocity in each rectangular jet is approximately 5800 cm s −1 . Following acceleration, particles larger than approximately 0.15 μm impact on quartz fiber strips, each 12.5×0.5 cm 2 , while the aerosol fraction smaller than 0.15 μm penetrates through the outlet of the impactor. The impactor operates at a flow rate 550 l min −1 and at a very low pressure drop of 0.020 kPa . The performance of the multi-slit impactor was validated in laboratory and the field tests. Laboratory experiments conducted with monodisperse PSL particles as well as polydisperse ammonium nitrate, sulfate and indoor aerosols corroborated the 50% cutpoint of the impactor at 0.15 μm . Field test comparisons between the high-volume multi-slit impactor and the Microorifice Uniform Deposit Impactor (MOUDI) showed that the accumulation and ultrafine mode concentrations of particulate nitrate, sulfate, elemental and organic carbon are in very good agreement (within 10% or less). This impactor has been developed primarily as a separator of ultrafine from accumulation mode particles for use in human exposure studies to concentrated ambient ultrafine aerosols. High-volume collection of size-fractionated particulate matter accomplished by this impactor further enables investigators in the field of environmental health to conduct toxicological studies using ambient accumulation and ultrafine mode particles in vitro as well as by means of intratracheal instillation.

Experimental studies on particle impaction and bounce: effects of substrate design and material

Abstract This paper presents an experimental investigation of the effects of impaction substrate designs and material in reducing particle bounce and reentrainment. Particle collection without coating by using combinations of different impaction substrate designs and surface materials was conducted using a personal particle sampler (PPS) developed by the University of Southern California. The PPS operates at flow rate of 4 lxa0min -1 with a 50% cutpoint of approximately 0.9xa0μm in aerodynamic diameter. The laboratory results showed that the PPS collection efficiency for particles larger than 50% cutpoint is strikingly low (e.g., less than 50%) when an uncoated open cavity made of aluminum was used as an impaction substrate. The collection efficiency gradually increased when Teflon tape, Nuclepore, and glass fiber filters were used as impaction surfaces, respectively. Conical or partially enclosed cavity substrate designs increased collection efficiency of particles of 9xa0μm up to 80–90%. A conical cavity with glass fiber filter used as impaction surface was identified as the optimum configuration, resulting in a collection efficiency of 92% at Stokes numbers as high as 15.4 (corresponding to 9xa0μm in aerodynamic diameter). Particle losses were low (less than 10%) and relatively independent of particle size in any design with glass fiber filter. Losses seemed to increase slightly with particle size in all other configurations. Finally, outdoor PM 1 concentrations obtained with the PPS (in its optimum configuration) and a modified micro-orifice uniform deposit impactor (MOUDI) with coated impaction stages were in excellent agreement. The mean ratio of the PPS-to-MOUDI concentration was 1.13(±0.17) with a correlation coefficient R 2 =0.95. Results from this investigation can be readily applied to design particle bounce-free impaction substrates without the use of coating. This is a very important feature of impactors, especially when chemical analysis of the collected particulate matter is desirable.