Michael D. Geller

Determination of Particle Effective Density in Urban Environments with a Differential Mobility Analyzer and Aerosol Particle Mass Analyzer

Effective densities of atmospheric aerosols in various locations of the Los Angeles Basin were determined by a DMA-APM technique. Effective density was calculated by comparing voltage distributions of sampled atmospheric aerosols with PSL particles of known density. The five sites chosen for field experiments were: (1) Interstate-710 Freeway, impacted by heavy-duty diesel vehicles; (2) State Route CA-110, open only to gasoline vehicles; (3) Riverside, a receptor site known for secondary particle formation; (4) University of Southern California, a typical urban and industrial environment; and (5) Coast for marine aerosol. The size range selected for this study was from 50 nm to 414 nm. While 50 nm particles exhibited a single effective density multiple effective densities were measured for each of the other particle sizes as significant fractions of these particles are transported from background sources. Regardless of location, 322–414 nm particle effective densities were considerably lower than unity. The lowest effective densities (∼ 0.1 g cm − 3 ) were reported for I-710, confirming that diesel combustion aerosols are rich in chain agglomerates with large void spaces. Riverside exhibited high effective densities (∼ 1.2–1.5 g cm − 3 ) for 50–202 nm particles, which we hypothesize is due to transformations that occur during advection from Los Angeles. Measurements of diurnal variation of effective density at Riverside support this hypothesis. Overall, our results suggest that effective density declines as the particle mobility diameter increases irrespective of location. Fractal dimensions calculated from average effective densities were lowest for I-710 ( D f = 2.41) and CA-110 (D f = 2.54) aerosols, presumably due to the influence of vehicular combustion emission on these sites. By contrast, average fractal dimensions at USC, Riverside and Coast were found to be 2.79, 2.83, and 2.92, respectively. High fractal dimensions at these sites may be the effects of aging, moisture absorption and/or organic vapor condensation on the particles, which fills void space and makes particles more spherical.

Altered heart-rate variability in asthmatic and healthy volunteers exposed to concentrated ambient coarse particles.

Twelve mildly asthmatic and four healthy adults were exposed to filtered air (FA) and concentrated ambient coarse particles (CCP) supplied to a whole-body exposure chamber via a coarse particle concentrator with 15 parallel virtual impactors. Exposures were conducted in a Los Angeles suburb with high levels of motor-vehicle pollution and lasted 2 h with intermittent exercise. Mean CCP concentration was 157 μ g/m 3 (range: 56–218 μ g/m3) measured by continuous monitoring with a tapered-element oscillating microbalance (TEOM). On average, 80% of mass was coarse (2.5–10 μ m aerodynamic diameter) and the rest < 2.5 μ m. Relative to FA, CCP exposure did not significantly alter respiratory symptoms, spirometry, arterial oxygen saturation, or airway inflammation according to exhaled nitric oxide and total and differential cell counts of induced sputum. After CCP exposure, Holter electrocardiograms showed small (p <. 05) increases in heart rate and decreases in heart-rate variability, which were larger in healthy than in asthmatic subjects. Cardiac ectopy did not increase. In conclusion, acute exposure to elevated concentrations of ambient coarse particles elicited no obvious pulmonary effects but appeared to alter the autonomic nervous system of the heart in adult volunteers.

Physical and Chemical Characteristics and Volatility of PM in the Proximity of a Light-Duty Vehicle Freeway

Abstract Volatility properties of ultrafine particles were analyzed next to State Route 110 (Pasadena freeway CA), a light-duty vehicle freeway where heavy-duty traffic is prohibited. In addition, mass concentration and chemical composition of particulate matter (PM) were measured in coarse, accumulation, and ultrafine modes. On weekdays from 17 May to 4 June 2004, measurements were performed in two locations, one very close to the freeway (within 2.5 m from the curb) and one at a distance of about 50 m from the freeway. For measurement of mass and chemical composition, the study employed in each location a micro-orifice uniform deposit impactor (MOUDI) and a modified high-volume sampler. Both instruments sampled with the same size cutpoints: a coarse mode from 2.5 to 10 μm, an accumulation mode from 0.18 to 2.5 μm, and an ultrafine mode of particles less than 0.18 μm in aerodynamic diameter. Alternately, a tandem differential mobility analyzer (TDMA) was used at the two sites. A heater between the two DMAs evaporated volatile material from the monodisperse aerosol, size selected by the first DMA. The second DMA analyzed the losses of volatile components. The ultrafine number concentrations next to the freeway were 46,000 cm−3 on average during the sampling period. The MOUDI ultrafine mass concentration, nitrate, and EC were higher next to the freeway than at the background site farther from the freeway. The other components analyzed in the ultrafine mode had similar concentrations next to the freeway and at the background site. Volatility ranged from about 65% volume losses of 120 nm particles heated to 110°C to 95% of 20 nm particles. The 20 nm aerosol was only internally mixed, whereas increasing nonvolatile fractions were found for 40 nm (6% next to the freeway), 80 nm (20%), and 120 nm (28%) aerosols.

Application of a Diffusion Charger for the Measurement of Particle Surface Concentration in Different Environments

Particle surface area has recently been considered as a possible metric in an attempt to correlate particle characteristics with health effects. In order to provide input to such studies, two Nanoparticle Surface Area Monitors (NSAMs, TSI, Inc.) were deployed in different urban sites within Los Angeles to measure the concentration levels and the diurnal profiles of the surface area of ambient particles. The NSAMs principle of operation is based on the unipolar diffusion charging of particles. Results show that the particle surface concentration decreases from ∼150 μ m2 cm−3 next to a freeway to ∼ 100 μ m2 cm−3 at 100 m downwind of the freeway, and levels decline to 50–70 μ m2 cm−3 at urban background sites. Up to 51% and 30% of the total surface area corresponded to particles < 40 nm next to the freeway and at an urban background site, respectively. The NSAM signal was well correlated with a reconstructed surface concentration based on the particle number size distribution measured with collocated Scanning Mobility Particle Sizers (SMPSs, TSI, Inc.). In addition, the mean surface diameter calculated by combination of the NSAM and the total particle number concentration measured by a Condensation Particle Counter (CPC, TSI, Inc.) was in reasonable agreement with the arithmetic mean SMPS diameter, especially at the urban site. This study corroborates earlier findings on the application of diffusion chargers for ambient particle monitoring by demonstrating that they can be effectively used to monitor the particle surface concentration, or combined with a CPC to derive the mean surface diameter with high temporal resolution.

Performance evaluation of a recently developed water-based condensation particle counter

This study provides an intercomparison of the performance of a newly developed water-based condensation particle counter (W-CPC) and a more widely used butanol-based CPC (TSI 3022A). Four test aerosols (ammonium nitrate, ammonium sulfate, adipic acid, and glutaric acid) were generated and tested in the laboratory before the instruments were deployed at four field locations (USC/downtown LA, I-710 Freeway, Pacific coast, and Los Angeles International Airport). Both instruments sampled the same incoming aerosol. Selected experiments utilized a differential mobility analyzer to select a particle size upstream of the CPCs. Evaluation of performance was based on the response of the instruments to varying particle composition, concentrations, and size. The results indicated good correlation between the two CPCs, with R2 values ranging from 0.74–0.99. Good agreement was found between the two instruments for particle concentrations between 0 and 40,000 particles/cm3, with W-CPC/TSI 3022A ratios between 0.8 and 1.2. Due to differences in the photometric mode calibration of these instruments, the ratio drops to 0.6–0.8 between 40,000–100,000 particles/cm3. However, the ratio rises again for lab aerosols above 100,000 particles/cm3 to 1.0–1.1. Results of this evaluation show that the W-CPC is a reliable particle– counting technology for particle concentrations encountered downstream of a DMA as well as in some ambient environments (< 40,000 particles/cm3).

Respiratory Responses to Exposures With Fine Particulates and Nitrogen Dioxide in the Elderly With and Without COPD

Elderly people, with and without chronic obstructive pulmonary disease (COPD), may be susceptible to particulate matter (PM) air pollution. However, the respiratory impacts of inhaled PM combined with copollutant(s) in controlled exposure studies are unclear and warrant investigation since exposures to PM–gas mixtures constitute realistic scenarios. Thus, we exposed 6 healthy subjects and 18 volunteers with COPD (mean age 71 yr) on separate days to (a) filtered air (FA); (b) 0.4 ppm NO2; (c) concentrated ambient particles (CAP), predominantly in the fine (PM2.5) size range, at concentrations near 200 μg/m3; and (d) CAP and NO2 together. Each 2-h exposure included exercise for 15 min every half hour. Most respiratory responses, including symptoms, spirometry, and total and differential counts of induced sputum cells, showed no statistically significant responses attributable to separate or combined effects of CAP and NO2. However, maximal mid-expiratory flow and arterial O2 saturation (measured by pulse oximetry) showed small but statistically significant decrements associated with CAP, greater in healthy than COPD subjects. CAP exposure was also associated with decreased percentages of columnar epithelial cells in sputum. The results suggest that the respiratory effect of the PM–NO2 mixture may be primarily PM driven since coexposure to NO2 did not significantly enhance the responses. In conclusion, older adults exposed to urban fine particles may experience acute small-airways dysfunction with impaired gas exchange. Healthy subjects appear more susceptible, suggesting that the respiratory effect may be related to efficient penetration and deposition of inhaled toxic particles in distal small airways. More clinical investigation of the elderly population is warranted.

Development and evaluation of a continuous coarse (PM10-PM2.5) particle monitor.

ABSTRACT In this paper, we describe the development and laboratory and field evaluation of a continuous coarse (2.5-10 um) particle mass (PM) monitor that can provide reliable measurements of the coarse mass (CM) concentrations in time intervals as short as 5-10 min. The operating principle of the monitor is based on enriching CM concentrations by a factor of ~25 by means of a 2.5-um cut point round nozzle virtual impactor while maintaining fine mass (FM)—that is, the mass of PM2 5 at ambient concentrations. The aerosol mixture is subsequently drawn through a standard tapered element oscillating microbalance (TEOM), the response of which is dominated by the contributions of the CM, due to concentration enrichment. Findings from the field study ascertain that a TEOM coupled with a PM10 inlet followed by a 2.5-um cut point round nozzle virtual impactor can be used successfully for continuous CM concentration measurements. The average concentration-enriched CM concentrations measured by the TEOM were 26-27 times higher than those measured by the time-integrated PM10 samplers [the micro-orifice uniform deposit

Observations of twelve USEPA priority polycyclic aromatic hydrocarbons in the Aitken size range (10-32 nm Dp)

Particle size distribution measurements of twelve USEPA priority pollutant polycyclic aromatic hydrocarbons (PAHs)—collected in Riverside, California, down to 10 nm aerodynamic diameter (Dp)—observed on integrated nocturnal samples (7:00 p.m.-6:30 a.m.) revealed that between 46 and 100% of the mass of particles in the Aitken size range was found in the 10–18 nm size bin. Particles in this size range have high alveolar deposition efficiency.

The Relationship between Real-Time and Time-Integrated Coarse (2.5–10 μm), Intermodal (1–2.5 μm), and Fine (<2.5 μm) Particulate Matter in the Los Angeles Basin

Abstract A periodic review of the National Ambient Air Quality Standards for Particulate Matter by the U.S. Environmental Protection Agency (EPA) will assess the standards with respect to levels, particle size, and averaging times. Some members of the scientific community in the United States and Europe have suggested the use of PM1 instead of PM2.5 as the fine particle measurement standard. This proposed standard is intended to reduce the influence of coarse particle sources on PM2.5, because some evidence suggests that PM1–2.5 is dominated by coarse particulate matter (PM) sources. In this study, coarse (PM2.5–10), intermodal (PM1–2.5), and fine (PM2.5) mass concentrations at four different sites are measured with continuous and time-integrated sampling devices. The main objective is to compare variations in these three size ranges while considering the effects of location, sources, weather, wind speed, and wind direction. Results show strong correlations between PM1 and intermodal PM in receptor sites. The contribution of PM1–2.5 to PM2.5 is highest in the summer months, most likely due to enhanced long-range transport. Coarse PM is poorly correlated with intermodal PM. Continuous data suggest that PM1 is growing into PM1–2.5 via complex processes involving stagnation of the aerosol during high relative humidity conditions, followed by advection during daytime hours

Development and Evaluation of a PM 10 Impactor-Inlet for a Continuous Coarse Particle Monitor

Conventional PM 10 inlets available operate at a flow rate of 16.7 l/min. The purpose of this study was to develop and test a PM 10 inlet designed to operate at 50 l/min to be used with a recently developed continuous coarse particle monitor (Misra et al.). Laboratory tests using polystyrene latex particles established the inlets 50% cutpoint at 9.5 w m. Further evaluation of PM 10 inlet was performed in a wind tunnel at wind speeds of 3, 8, and 24 km/h. Tests showed that the 50% efficiency cutpoint as well as the very sharp particle separation characteristics of the inlet were maintained at these wind speeds. Field evaluation of the PM 10 inlet was performed in Riverside and Rubidoux, CA. A 2.5 w m cutpoint round nozzle virtual impactor was attached downstream of the developed PM 10 inlet. The Dichotomous PM 10 Partisol Sampler, operating at a flow rate of 16.7 l/min was used as a reference sampler. The Dichotomous Partisol uses an FRM PM 10 inlet operating at 16.7 l/min to remove particles larger than 10 w m in aerodynamic diameter. Commercially available 4.7 cm Teflon filters were used in both the Partisol and the PM 10 inlet to collect particulate matter (PM). Results showed good agreement between coarse PM (2.5-10 w m) mass concentrations measured by means of the PM 10 inlet and Partisol. Chemical analyses showed excellent agreement between coarse PM concentrations of Al, K, Si, Ca, and Fe obtained by the two samplers. The agreement also persisted for nitrate and sulfate. Finally, the excellent agreement between coarse concentrations of the PM 10 inlet and Partisol persisted for wind speeds up to 19 km/h.