CAPS: 2005 Publications

Kinetic data for multiple OH-alkane reactions, including primary kinetic isotope data, can be fit simultaneously to extract constrained contributions from transition state vibrational activation, zero-point energy, and tunneling. We use data for single-pathway reactions: OH + methane, ethane, and cyclohexane, to obtain optimal 'intrinsic' parameters common to all reactions. This is possible because parameters specific to individual reactions, such as the pre-exponential term, can be accurately calculated with ease. Several intrinsic parameters - the barrier height, the tunneling temperature (imaginary frequency) and a transition state bending frequency (the radical attack angle) - scale together from reaction to reaction. This scaling is so precise that we can accurately fit data for OH + methane using intrinsic parameters derived for OH + ethane and OH + cyclohexane using only a single free parameter (the scaling factor). This strongly confirms our underlying hypothesis about the physics controlling the key transition state parameters and suggests that extrapolations in temperature and predictions for unmeasured reactions are potentially robust. (c) 2005 Elsevier B.V. All rights reserved. C1 Carnegie Mellon Univ, Dept Chem & Chem Engn, Pittsburgh, PA 15213 USA.

We report secondary organic aerosol (SOA) yields from the ozonolysis of alpha-pinene under both dark and UV-illuminated conditions. Exposure to UV light reduces SOA yield by 20-40%, with a maximum reduction in yield coinciding with a minimum in the amount of terpene consumed (15-30 ppb). The data are consistent with a constant absolute reduction in the yield of similar to 0.03. Gas chromatography mass spectrometry analysis of filter samples indicates that the major products found in alpha-pinene SOA include organic acids (e.g., pinic acid), keto acids (e.g., pinonic acid), and hydroxy keto acids (e.g., 10-hydroxypinonic acid), Analysis of filter-based results suggests that yield reduction is a result of the formation of a more volatile product distribution when experiments are conducted in the presence of UV light. These results imply that previous dark bag experiments may overestimate SOA generation from monoterpenes and also that SOA generation in the atmosphere may depend significantly on actinic flux. C1 Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.

We report secondary organic aerosol (SOA) yields from the ozonolysis of alpha-pinene in the presence of NO and NO2. Experimental conditions are characterized by the [VOC](0)/ [NOx](0) ratio (ppbC/ppb), which varies from similar to 1 to similar to 300. SOA yield is constant for [VOC](0)/[NOx](0) > similar to 15 and decreases dramatically (by more than a factor of 4) as [VOC](0)/[NOx](0) decreases. Aerosol production is completely suppressed in the presence of NO for [VOC](0)/[NOx](0) <= 4.5. Fourier transform IR analysis of filter samples reveals that nitrate-containing species contribute significantly to the total aerosol mass at low [VOC](0)/[NOx](0). Yield reduction is a result of the formation of a more volatile product distribution as [VOC](0)/[NOx](0) decreases; we propose that the change in the product distribution is driven by changes in the gas-phase chemistry as NOx concentration increases. We also present two-product model parameters to describe aerosol production from the alpha-pinene/O-3/NOx system under both highand low-NOx conditions. C1 Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.

A substantial fraction of the total ultrafine particulate mass is comprised of organic compounds. Of this fraction, a significant subfraction is secondary organic aerosol (SOA), meaning that the compounds are a by-product of chemistry in the atmosphere. However, our understanding of the kinetics and mechanisms leading to and following SOA formation is in its infancy. We lack a clear description of critical phenomena; we often don't know the key, rate limiting steps in SOA formation mechanisms. We know almost nothing about aerosol yields past the first generation of oxidation products. Most importantly, we know very little about the derivatives in these mechanisms; we do not understand how changing conditions, be they precursor levels, oxidant concentrations, co-reagent concentrations (i.e., the VOC/NOx ratio) or temperature will influence the yields of SOA. In this paper we explore the connections between fundamental details of physical chemistry and the multitude of steps associated with SOA formation, including the initial gas-phase reaction mechanisms leading to condensible products, the phase partitioning itself, and the continued oxidation of the condensed-phase organic products. We show that SOA yields in the alpha-pinene + ozone are highly sensitive to NOx, and that SOA yields from beta-caryophylene + ozone appear to increase with continued ozone exposure, even as aerosol hygroscopicity increases as well. We suggest that SOA yields are likely to increase substantially through several generations of oxidative processing of the semi-volatile products. C1 Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Univ Iowa, Dept Chem Engn, Iowa City, IA 52242 USA. Univ Copenhagen, Dept Chem, DK-2100 Copenhagen, Denmark. Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Univ Patras, Dept Chem Engn, GR-26500 Patras, Greece.

We develop relative kinetics for heterogeneous oxidation of multi-component organic aerosols. Common accommodation, diffusion, and deposition terms cancel in this formulation, and rate constants may be determined for many compounds simultaneously within an aerosol with a realistic composition. Finally, cross-phase relative rate constants with a gas-phase reference compound and a condensed-phase target compound provide effective rate constants for use in atmospheric models. C1 Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA.

The ability of biogenic secondary organic aerosol (SOA) to contribute to the concentration of cloud condensation nuclei (CCN) in the atmosphere is examined. Aerosol is generated by the ozonolysis reaction of monoterpenes (alpha-pinene, beta-pinene, 3-carene, and limonene) and sesquiterpenes (beta-caryophyllene, alpha-humulene, and alpha-cedrene) in a 10 m(3) temperature-controlled Teflon smog chamber. In some cases, a self-seeding technique is used, which enables high particle concentrations with the desired diameters without compromising particle composition and purity. The monoterpene SOA is excellent CCN material, and it activates similarly (average activation diameter equals 48 +/- 8 nm at 1% supersaturation for the species used in this work) to highly water-soluble organic species. Its effective solubility in water was estimated to be in the range of 0.07-0.40 g solute/g H2O. CCN measurements for sesquiterpene SOA (average activation diameter equals 120 +/- 20 nm at 1% supersaturation for the species used in this work) show that it is less CCN active than monoterpene SOA. The initial terpene mixing ratio (between 3 and 100 ppb) does not affect the CCN activation for freshly generated SOA. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Univ Copenhagen, Dept Chem, DK-2100 Copenhagen, Denmark. Bucknell Univ, Dept Chem Engn, Lewisburg, PA 17837 USA. Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Univ Patras, Dept Chem Engn, GR-26110 Patras, Greece.

[1] Primary and secondary contributions to ambient levels of volatile organic compounds (VOCs) and aerosol organic carbon (OC) are determined using measurements at the Pittsburgh Air Quality Study (PAQS) during January - February and July - August 2002. Primary emission ratios for gas and aerosol species are defined by correlation with species of known origin, and contributions from primary and secondary/biogenic sources and from the regional background are then determined. Primary anthropogenic contributions to ambient levels of acetone, methylethylketone, and acetaldehyde were found to be 12 - 23% in winter and 2 - 10% in summer. Secondary production plus biogenic emissions accounted for 12 - 27% of the total mixing ratios for these compounds in winter and 26 - 34% in summer, with background concentrations accounting for the remainder. Using the same method, we determined that on average 16% of aerosol OC was secondary in origin during winter versus 37% during summer. Factor analysis of the VOC and aerosol data is used to define the dominant source types in the region for both seasons. Local automotive emissions were the strongest contributor to changes in atmospheric VOC concentrations; however, they did not significantly impact the aerosol species included in the factor analysis. We conclude that longer-range transport and industrial emissions were more important sources of aerosol during the study period. The VOC data are also used to characterize the photochemical state of the atmosphere in the region. The total measured OH loss rate was dominated by nonmethane hydrocarbons and CO (76% of the total) in winter and by isoprene, its oxidation products, and oxygenated VOCs (79% of the total) in summer, when production of secondary organic aerosol was highest. C1 Univ Calif Berkeley, Dept ESPM Ecosyst Sci, Div Ecosyst Sci, Berkeley, CA 94720 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Rutgers State Univ, Dept Environm Sci, New Brunswick, NJ 08901 USA.

The effects of size-dependent fog chemistry and physics on the pre-fog aerosol size/composition distribution are examined for a San Joaquin Valley fog. In this paper, we compare the results of a size-resolved fog model with measurements from Colorado State University's five-stage and bulk cloud collectors. The model reproduces the amounts and trends of the observed bulk fog water concentrations and size-dependent composition of the major species (sulfate, ammonium, nitrate, sodium, chloride, calcium). We examine the size-dependent evolution of the measured species and compare sulfate concentrations predicted by the highly size-resolved fog model with the variable size resolution model (VSRM) [Fahey and Pandis, 2001. Atmospheric Environment 35, 4471-4478]. It is shown that for lengthy fog events in relatively clean environments deposition of fog droplets is the most important process for the evolution of the size/composition distribution of aerosols over the course of fog processing. The results indicate a need for a larger number of measurements of deposition fluxes for individual species and the need for aqueous-phase concentration measurements from the early formation stage of fogs. (c) 2005 Elsevier Ltd. All rights reserved. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Colorado State Univ, Dept Atmospher Sci, Ft Collins, CO 80523 USA.

The effect of concentrating semi-volatile aerosols using a water-condensation technology was investigated using the Versatile Aerosol Concentration Enrichment System (VACES) and the Aerodyne Aerosol Mass Spectrometer (AMS) during measurements of ambient aerosol in Pittsburgh, PA. It was found that the shape of the sulfate mass-weighed size distribution was approximately preserved during passage through the concentrator for all the experiments performed, with a mass enhancement factor of about 10-20 depending on the experiment. The size distributions of organics, ammonium and nitrate were preserved on a relatively clean day (sulfate concentration around 7 mu g/m(3)), while during more polluted conditions the concentration of these compounds, especially nitrate, was increased at small sizes after passage through the concentrator. The amount of the extra material, however, is rather small in these experiments: between 2.4% and 7.5% of the final concentrated PM mass is due to artifact condensation. An analysis of thermodynamic processes in the concentrator indicates that the extra particle material detected can be explained by redistribution of gas-phase material to the aerosol phase in the concentrator. The analysis shows that the condensation of extra material is expected to be larger for water-soluble semi-volatile material, such as nitrate, which agrees with the observations. The analysis also shows that artifact formation of nitrate will be more pronounced in ammonia-limited conditions and virtually undetectable in ammonia-rich conditions. (c) 2004 Elsevier Ltd. All rights reserved. C1 Duke Univ, Dept Civil & Environm Engn, Durham, NC 27708 USA. Univ Colorado, Dept Chem, Boulder, CO 80309 USA. Univ Colorado, CIRES, Boulder, CO 80309 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Aerodyne Res Inc, Ctr Aerosol & Cloud Chem, Billerica, MA 01821 USA. Univ So Calif, Dept Civil & Environm Engn, Los Angeles, CA 90089 USA.

The present paper reviews existing knowledge with regard to Organic Aerosol ( OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol ( SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The upto- date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies. C1 Univ Crete, Dept Chem, Environm Chem Proc Lab, Iraklion 71409, Greece. CALTECH, Pasadena, CA 91125 USA. Univ Patras, Dept Chem Engn, GR-26110 Patras, Greece. Berg Univ Wuppertal, Phys Chem FB C, D-42119 Wuppertal, Germany. JRC, Climate Change Unit, Inst Environm & Sustainabil, Ispra, Italy. CNR, Ist Sci Atmosfera & Clima, I-00185 Rome, Italy. Colorado State Univ, Cooperat Inst Res Atmosphere, Ft Collins, CO 80523 USA. Georgia Inst Technol, Sch Earth & Atmospher Sci, Atlanta, GA 30332 USA. Georgia Inst Technol, Sch Chem & Biomol Engn, Atlanta, GA 30332 USA. Univ Oslo, Dept Chem, Oslo, Norway. Lund Univ, Dept Phys, Div Nucl Phys, Lund, Sweden. CEA, CNRS, LSCE, F-91198 Gif Sur Yvette, France. Max Planck Inst Chem, Div Atmospher Chem, D-6500 Mainz, Germany.

[1] Airborne particulate size distribution data acquired in Pittsburgh from July 2001 to June 2002 were analyzed as a bilinear receptor model solved by positive matrix factorization (PMF). The data were obtained from two scanning mobility particle spectrometers and an aerodynamic particle sampler with a temporal resolution of 15 min. Each sample contained 165 size bins from 0.003 to 2.5 mm. Particle growth periods in nucleation events were identified, and the data in these intervals were excluded from this study so that the size distribution profiles associated with the factors could be regarded as sufficiently constant to satisfy the assumptions of the receptor model. The values for each set of five consecutive size bins were averaged to produce 33 new size intervals. Analyses were made on monthly data sets to ensure that the changes in the size distributions from the source to the receptor site could be regarded as constant. The factors from PMF could be assigned to particle sources by examination of the number size distributions associated with the factors, the time frequency properties of the contribution of each source ( Fourier analysis of source contribution values), and the correlations of the contribution values with simultaneous gas phase measurements (O-3, NO, NO2, SO2, CO) and particle composition data ( sulfate, nitrate, organic carbon/elemental carbon). Seasonal trends and weekday/weekend effects were investigated. Conditional probability function analyses were performed for each source to ascertain the likely directions in which the sources were located. Five factors were separated. Two factors, local traffic and nucleation, are clear sources, but each of the other factors appears to be a mixture of several sources that cannot be further separated. C1 Clarkson Univ, Ctr Air Resources Engn & Sci, Potsdam, NY 13699 USA. Clarkson Univ, Dept Chem Engn, Potsdam, NY 13699 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Providence Engn & Environm Grp LLC, Baton Rouge, LA 70808 USA.

In the eastern United States, inorganic species account for approximately half of the PM2.5 mass, with sulfate salts comprising the largest fraction. Current strategies for reducing PM2.5 mass concentrations target reducing SO2 to reduce sulfate, but in such a case more ammonium nitrate may form when nitric acid is present. Large-scale chemical transport models suffer from uncertainties associated with emission inventories. To examine how the inorganic PM2.5 concentration responds to changes in emissions, we introduce an observation-based box model, the thermodynamic model with removal (TMR), to estimate responses of PM2.5 to precursor concentrations. TMR assumes that particles are in equilibrium with the gas phase, but the removal rate of total (PM2.5 + gas) nitric acid from the system depends on the gas/aerosol partitioning of this species. The model is used to investigate sulfate, total ammonia, and total nitric acid control strategies for western Pennsylvania during the winter using measurements obtained in the Pittsburgh Air Quality Study. Predictions from TMR are compared with observations and predictions of a chemical equilibrium model (GFEMN), where the perturbation of sulfate or total ammonia does not affect the total nitric acid availability. Results show that TMR predicts more aerosol nitrate to form than GFEMN in scenarios where the total ammonia to sulfate ratio is increased, but model results are similar under ammonia-limited conditions. When sulfate is reduced by 50% during the winter, GFEMN predicts that inorganic PM2.5 mass concentrations will be reduced by 23%, while TMR predicts that there will only be an 8% reduction. For a 50% reduction in ammonia availability, inorganic PM2.5 was reduced by 29%, while for a 50% reduction in total nitric acid a 17% reduction in inorganic PM2.5 was predicted. The analysis suggests the importance of the phase state of the aerosol for the effectiveness of the emission control strategies. C1 Univ Ioannina, Dept Environm & Nat Resources Management, GR-30100 Agrinion, Greece. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.

Two multivariate data analysis methods, partial least square ( PLS) and positive matrix factorization ( PMF), were used to analyze aerosol size distribution data and composition data. The relationships between the size distribution data and composition data were investigated by PLS. Three latent variables summarized chemical composition data and most variations in size distribution data especially for large particles and proved the existence of the linearity between the two data sets. The three latent variables were associated with traffic and local combustion sources, secondary aerosol, and coalfired power plants. The size distribution, particle composition, and gas composition data were combined and analyzed by PMF. Source information was obtained for each source using size distribution and chemical composition simultaneously. Eleven sources were identified: secondary nitrate 1 and 2, remote traffic, secondary sulfate, lead, diesel traffic, coal- fired power plant, steel mill, nucleation, local traffic, and coke plant. C1 Clarkson Univ, Dept Chem Engn, Ctr Air Resources Engn & Sci, Potsdam, NY 13699 USA. Univ Maryland, Dept Chem & Biochem, College Pk, MD 20742 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Univ Iowa, Dept Chem & Biochem Engn, Iowa City, IA 52242 USA. Providence Engn & Environm Grp LLC, Baton Rouge, LA 70808 USA.

The aerosol water content and volumetric growth factors of fine particulate matter were measured during July-August 2001 and January-June 2002 in an urban park about 6 km from downtown Pittsburgh, Pennsylvania. Most of the aerosol during the study was transported to the region from other areas, and its composition and concentration were characteristic of the regional particulate matter in the northeastern United States. During the summer months the ambient aerosol practically always contained water even when the relative humidity ( RH) was as low as 30%. In contrast, during the winter the aerosol was dry below 60% RH. The spring months were characterized by a transitional behavior between these two states. The observed seasonal behavior can be explained by the aerosol acidity. The summer aerosol was acidic and retained water at low RH. The winter aerosol was neutral and became wet when the relative humidity reached the deliquescence point of ammonium nitrate. The observations during July 2001 were compared with the predictions of the thermodynamic Gibbs Free Energy Minimization (GFEMN) model and the aerosol inorganics model ( AIM), neglecting the organic aerosol contribution to water absorption. The models under-predicted water concentrations by about 35%, but no clear correlation between organic mass and the excess water was observed. On average, the contribution of the organics to water absorption appeared to be higher during the afternoon hours and when the aerosol was presumably more oxidized. C1 Duke Univ, Dept Civil & Environm Engn, Durham, NC 27708 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.

The creation of new atmospheric particles from in situ nucleation influences climate through cloud-aerosol interactions and may negatively impact human health. Although recent observations show that nucleation is widespread in the eastern United States, the corresponding pathways remain uncertain. Combining extensive field measurements in Pittsburgh, Pennsylvania, with an aerosol dynamics and chemistry model assuming ternary NH3-H2SO4-H2O nuclei formation, we show excellent model-measurement agreement and predictive capability. The ternary NH3-H2SO4-H2O nucleation model is successful in predicting the presence or lack of nucleation on 19 out of 19 days with complete data sets in July 2001 and on 25 out of 29 days in January 2002. Reductions of ammonia emissions are predicted to decrease the frequency of nucleation events during both summer and winter, with a more dramatic effect during the summer. The response to changes in emissions of sulfur dioxide during the summer is counterintuitive. Reductions of sulfur dioxide and the resulting sulfate by up to 40% actually increase the frequency of the summer nucleation events. Modeling predicts the opposite effect in winter, with reductions of sulfur dioxide leading to fewer nucleation events. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA.

This paper presents a fine particle emission profile for a large metallurgical coke production facility. The profile is developed from highly time-resolved, ambient air quality measurements made at a fence line site adjacent to the plant. A fence line approach was employed because the coke plant has hundreds of stacks and other emission points, making it difficult to develop an integrated, facility-wide emission profile using stack sampling techniques. Continuous or semi-continuous measurements of PM2.5 mass, PM10 mass, SO2, NOx, organic and elemental carbon (OC and EC), particle size and number, I I trace metals, wind direction and wind speed were made. Background pollutant levels were also measured. A combination of highly time-resolved meteorology and air quality data were used to determine when the coke facility emissions influenced the sampling site. Concentrations for most pollutants at the fence line site were one to two orders of magnitude higher than background levels when the facility plume heavily influenced the fence line site. Highly time-resolved measurements are essential to resolve these relatively short-duration, large spikes in pollutant concentrations. Simply measuring wind direction is insufficient. From these highly time-resolved measurements an average PM2.5 emission profile for the coke facility was developed. The profile is dominated by OC (40% +/- 9% of PM2.5 mass emissions) and EC (25% +/- 5% of PM2.5 mass emissions). Significant contributions of certain trace metals were also observed, including As, Zn, Se, and Pb. The particle emissions are dominated by the fine fraction, with PM2.5 estimated to contribute 84% +/- 14% of the PM10 mass. (c) 2005 Elsevier Ltd. All rights reserved. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Univ Maryland, Dept Chem & Biochem, College Pk, MD 20742 USA. Rutgers State Univ, Dept Environm Sci, New Brunswick, NJ 08903 USA.

The size and complexity of current dilution samplers is a major barrier to more widespread application of these systems for source characterization. A new, more portable dilution sampler has been designed to provide measurements consistent with the widely cited Caltech dilution sampler. Intercomparison experiments were performed using a diesel engine and wood stove to evaluate the comparability of the new design with a sampler based on the Caltech design. These experiments involved simultaneous operation of multiple dilution samplers from the same source. Filter based measurements included PM2.5 mass, organic carbon, and elemental carbon emissions. Particle size distributions in the range from 10 - 480 nm were measured using a scanning mobility particle sizer. The filterbased and integrated-total volume measurements made with the two designs are in good agreement. For example, the average relative bias between the two samplers of PM2.5 mass emission rate measured with Teflon filters is 1%. Nucleation was intermittently observed in the sampler based on the Caltech design, but rarely observed in the new design. Significant discrepancies in total number emissions between the two samplers occurred during periods of nucleation. Experiments were also conducted to examine the effects of residence time on the diluted emissions. No changes in the filterbased or integrated volume measurements were observed with an additional 40-s residence time, indicating that phase equilibrium is established in the 2.5 s of residence time provided by the dilution tunnel. This conclusion is consistent with theoretical analysis. These results provide new insight into the effects of dilution sampling on measurements of fine particle emissions, providing important data for the ongoing effort of the EPA and ASTM to define a standardized dilution sampling methodology for characterizing emissions from stationary combustion sources. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA.

The inputs and outputs of airborne lead in the South Coast Air Basin of California (SOCAB) are quantified according to standard mass balance calculations. Results for 2001 show that approximately 49 000 kg of lead exit the Basin each year, but traditional sources contribute only about 6500 kg of lead each year. We resolve this discrepancy through a simple computer model that quantifies the resuspension of lead-containing particles. Our results suggest that these lead particles were deposited during the years of leaded gasoline use and that resuspension is responsible for generating an additional 54 000 kg of airborne lead each year. This agrees roughly with estimated outputs. Thus, we conclude that resuspension, although an insignificant source of airborne lead during the era of leaded fuel, became a principal source in the SOCAB as lead emissions from vehicles declined. The results of the resuspension model further suggest that soil lead levels will remain elevated for many decades, in which case resuspension will remain a major source well into the future. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA.

Results of recent research show that particulate matter ( PM) composition and size vary widely with both space and time. Despite the variability in PM characteristics, which are believed to influence human health risks, the observed relative health risk estimates per unit PM mass falls within a narrow range of values. Furthermore, no single chemical species appears to dominate health effects; rather the effects appear to be due to a combination of species. Non-PM factors such as socioeconomic status and lifestyle are also believed to affect the health risk, although accounting for these confounding factors is challenging. Airborne PM is also responsible for a number of effects aside from human health, such as alterations in visibility and climate. Because the PM problem is associated with a range of societal issues such as energy production and economic development, making progress on reducing the effects of PM will require integrated strategies that bring together scientists and decision makers from different disciplines to consider tradeoffs holistically. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn & Publ Policy, Pittsburgh, PA 15213 USA. Univ Calif Irvine, Dept Community & Environm Med, Irvine, CA 92717 USA. US EPA, Las Vegas, NV 89193 USA.

A microwave-assisted digestion procedure using HNO3, HF, and H2O2 has been developed for analysis of elements in ambient particulate matter (PM). The samples are collected on cellulose filters and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS is calibrated with external standards, and recovery of analytes is tested with NIST SRM 1648 Urban Dust. This method has been used to quantify the airborne concentrations of a large number of elements, including Ag, As, Ba, Be, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, K, Li, Mg, Mn, Mo, Ni, Pb, Rb, Se, Sb, Sr, Ti, Tl, V, and Zn. For the majority of these elements, recovery of the NIST SRM is within 15% of the certified values. (c) 2005 Elsevier B.V. All rights reserved. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA.