CAPS: 2006 Publications

Despite the success of the CRESU (Cinetique de Reaction en Ecoulement Supersonique Uniforme) method in measuring rate coefficients for neutral- neutral reactions of radicals down close to the very low temperatures prevalent in dense interstellar clouds (ISCs), there are still many reactions of potential importance in the chemistry of these objects for which there have been no measurements of low temperature rate coefficients. One important class of reactions is that between atomic and molecular free radicals and unsaturated hydrocarbons; that is, alkynes and alkenes. Based on semi-empirical arguments and correlations of `room temperature' rate coefficients, k(298 K), for reactions of this type with the difference between the ionisation energy of the alkyne/alkene and the electron affinity of the radical, we suggest which reactions between the radicals, C(3P), O(3P), N(4S), CH, C2H and CN, and carbon chain molecules (Cn) and cyanopolyynes (HC2nCN and NCC2nCN) are likely to be fast at the temperature of dense ISCs. These reactions and rate coefficients have been incorporated into a purely gas-phase model (osu2005) of ISC chemistry. The results of these calculations are presented and discussed.

We present estimates of the vehicular contribution to ambient organic carbon (OC) and fine particle mass (PM) in Pittsburgh, PA using the chemical mass balance (CMB) model and a large dataset of ambient molecular marker concentrations. Source profiles for CMB analysis are selected using a method of comparing the ambient ratios of marker species with published profiles for gasoline and diesel vehicle emissions. The ambient wintertime data cluster on a hopanes/EC ratio-ratio plot, and therefore can be explained by a large number of different source profile combinations. In contrast, the widely varying summer ambient ratios can be explained by a more limited number of source profile combinations. We present results for a number of different CMB scenarios, all of which perform well on the different statistical tests used to establish the quality of a CMB solution. The results illustrate how CMB estimates depend critically on the marker-to-OC and marker-to-PM ratios of the source profiles. The vehicular contribution in the winter is bounded between 13% and 20% of the ambient OC (274 +/- 56-416 +/- 72 ng-cm(-3)). However, variability in the diesel profiles creates uncertainty in the gasoline-diesel split. On an OC basis, one set of scenarios suggests gasoline dominance, while a second set indicates a more even split. On a PM basis, all solutions indicate a diesel-dominated split. The summer CMB solutions do not present a consistent picture given the seasonal shift and wide variation in the ambient hopanes-to-EC ratios relative to the source profiles. If one set of source profiles is applied to the entire dataset, gasoline vehicles dominate vehicular OC in the winter but diesel dominates in the summer. The seasonal pattern in the ambient hopanes-to-EC ratios may be caused by photochemical decay of hopanes in the summer or by seasonal changes in vehicle emission profiles. (c) 2006 Elsevier Ltd. All rights reserved. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Florida Int Univ, Dept Civil & Environm Engn, Miami, FL 33199 USA.

Individual organic compounds often referred to as molecular markers are used in conjunction with the chemical mass balance (CMB) model to apportion sources of primary organic aerosol. This paper presents a methodology to visualize molecular marker data; it allows comparison of ambient data and source profiles and allows assessment of chemical stability and aging. The method is intended to complement traditional quantitative source apportionment analysis. The core of the technique involves construction of plots of ratios of species concentrations (ratio-ratio plots) in which source profiles appear as points connected by linear mixing lines. The approach is illustrated using data collected over a 1-year period in Pittsburgh, Pennsylvania. The analysis considers for elemental carbon and a number of high molecular weight polycyclic aromatic hydrocarbons (PAHs) commonly used as molecular markers in CMB: benzo(b+j+k)fluoranthene, benzo(e) pyrene, benzo[ g, h, i] perylene, coronene, and indeno(1,2,3-cd) pyrene. In Pittsburgh, the ambient concentrations of these PAHs are higher than in other cities in the United States; they are also strongly correlated consistent with a single, dominant source. Both ratio-ratio plots and CMB analysis indicate that this source is metallurgical coke production. Although emissions from coke production dominate ambient PAH concentrations, on most study days they contributed little fine particle mass. Ratio-ratio plots are then used to investigate the feasibility of using PAHs to help differentiate between gasoline and diesel vehicle emissions. Ambient concentrations of these large PAHs provide little information on the gasoline-diesel split because of the strong influence of local emissions from coke production combined with evidence of photochemical decay of PAHs in the regional air mass. Decay of PAHs will bias estimates of the gasoline-diesel split toward diesel emissions. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Florida Int Univ, Dept Divil & Environm Engn, Miami, FL 33199 USA. Florida Int Univ, Dept Civil & Environm Engn, Miami, FL 33199 USA.

Chemical mass balance analysis was performed using a large dataset of molecular marker concentrations to estimate the contribution of biomass smoke to ambient organic carbon (OC) and fine particle mass in Pittsburgh, Pennsylvania. Source profiles were selected based on detailed comparisons between the ambient data and a large number of published profiles. The fall and winter data were analyzed with fireplace and woodstove source profiles, and open burning profiles were used to analyze the spring and summer data. At the upper limit, biomass smoke is estimated to contribute on average 520 +/- 140 ng-C m(-3) or 14.5% of the ambient OC in the fall, 210 +/- 85 ng-C m(-3) or 10% of the ambient OC in the winter, and 60 +/- 21 ng-C/m(-3) or 2% of the ambient OC in the spring and summer. In the fall and winter, there is large day-to-day variability in the amount of OC apportioned to biomass smoke. The levels of biomass smoke in Pittsburgh are much lower than in some other areas of the United States, indicating significant regional variability in the importance of biomass combustion as a source of fine particulate matter. The calculations face two major sources of uncertainty. First, the ambient ratios of levoglucosan, resin acids, and syringhaldehyde concentrations are highly variable implying that numerous sources with distinct source profiles contribute to ambient marker concentrations. Therefore, in contrast to previous CMB analyses, we find that at least three distinct biomass smoke source profiles must be included in the CMB model to explain this variability. Second, the marker-to-OC ratios of available biomass smoke profiles are highly variable. This variability introduces uncertainty of more than a factor of 2 in the amount of ambient OC apportioned to biomass smoke by different statistically acceptable CMB solutions. The marker-to-OC ratios of source profiles are critical parameters to consider when evaluating CMB solutions. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Florida Int Univ, Dept Civil & Environm Engn, Miami, FL 33199 USA.

The chemical mass balance model is applied to a large dataset of organic molecular marker concentrations to apportion ambient organic aerosol to food cooking emissions in Pittsburgh, Pennsylvania. Ambient concentrations of key cooking markers such as palmitoleic acid, oleic acid, and cholesterol are well correlated, which implies the existence of well-defined source profiles. However, significant inconsistencies exist between the ambient data and published source profiles. Most notably, the ambient ratio of palmitoleic-acid-to-oleic-acid is more than a factor of 10 greater than essentially all published source profiles. This problem is not unique to Pittsburgh. The reason for this discrepancy is not known but it means that both acids cannot be fit simultaneously by CMB. CMB analysis is performed using three different combinations of food cooking source profiles and molecular markers. Although all three solutions have high statistical quality, the amount of OC apportioned to food cooking emissions varies by a factor of 9. Differences in fitting species and source profile marker-to-organic-carbon ratios cause most of the large systematic biases between the different solutions. The best CMB model includes two alkanoic acids as fitting species in addition to other cooking markers, which helps constrain the source contribution estimates. It also includes two meat cooking source profiles to account for the variability in the ambient data. This model apportions 320 +/- 140 ng-C m(-3) or 10% of the study average ambient organic carbon to food cooking emissions. Although these results illustrate the significant challenges created by source profile variability, the strong correlations in the ambient dataset underscore the significant promise that molecular markers hold for source apportionment analysis. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Florida Int Univ, Dept Civil & Environm Engn, Miami, FL 33199 USA.

Limonene has a high emission rate both from biogenic sources and from household solvents. Here we examine the limonene + ozone reaction as a source for secondary organic aerosol (SOA). Our data show that limonene has very high potential to form SOA and that NOx levels, O-3 levels, and UV radiation all influence SOA formation. High SOA formation is observed under conditions where both double bonds in limonene are oxidized, but those conditions depend strongly on NOx. At low NOx, heterogeneous oxidation of the terminal double bond follows the initial limonene ozonolysis (at the endocyclic double bond) almost immediately, making the initial reaction rate limiting. This requires a high uptake coefficient between ozone and the first-generation, unsaturated organic particles. However, at high NOx, this heterogeneous processing is inhibited and gas-phase oxidation of the terminal double bond dominates. Although this chemistry is slower, it also yields products with low volatility. UV light suppresses production of the lowest volatility products, as we have shown in earlier studies of the R-pinene + ozone reaction. C1 Carnegie Mellon Univ, Ctr Atmospher Particle Studies, Pittsburgh, PA 15213 USA.

Several recent experimental studies have provided substantial new constraints for the mechanisms on the HNO3 potential energy surface. These include observations of biexponential OH decay over short time scales from OH + NO2, which constrain key properties of the short-lived HOONO intermediate, observations of both conformers of the HOONO intermediate itself, isotopic scrambling data for (OH)-O-18 + NO2, and observations of HONO2 production from the HO2 + NO reaction. We combine all of these recent data in a master-equation simulation of the system. This simulation is initialized with computational values for both stable species (wells) and transition states, but parameters are then adjusted to fit the observations. All parameters are kept within limits defined by experimental and theoretical uncertainty, and all converge away from their bounds. The primary fitting is carried out on the OH kinetic datas-we first fit the biexponential kinetics, then address the isotopic scrambling. Isotopic scrambling is shown to be rapid but not complete at low pressure, while at least two parameter sets are shown to be consistent with the biexponential data. Of these two parameter sets, one is far more consistent with recent observations of trans-HOONO decay, isotopic scrambling, and HONO2 production from HO2 + NO. This we regard as the most probable potential energy surface for the reaction. On this PES, cis-trans isomerization for HOONO is slow but isomerization of trans-HOONO to HONO2 is rapid. This has significant implications for observed HOONO behavior and also HONO2 formation in the atmosphere from both HO2 + NO and OH + NO2. C1 Carnegie Mellon Univ, Dept Chem & Chem Engn, Pittsburgh, PA 15213 USA.

We present a method for measuring secondary organic aerosol (SOA) production at low total organic mass concentration (C-OA) using proton-transfer reaction mass spectrometry (PTR-MS). PTR-MS provides high time resolution measurements of gas-phase organic species and, coupled with particle measurements, allows for the determination of aerosol yield in real time. This approach facilitates the measurement of aerosol production at low C-OA; in fact aerosol mass fractions can be measured during alpha-pinene consumption as opposed to only at the completion of gas-phase chemistry. The high time resolution data are consistent with both the partitioning theory of Pankow (Atmos. Environ. 1994, 28, 185 and 189) and the previous experimental measurements. Experiments including the effect of UV illumination and NOx reveal additional features of alpha-pinene + ozone product photochemistry and volatility. The high time resolution data also elucidate aerosol production from alpha-pinene ozonolysis at C-OA < 10 mu g m(-3) and show that extrapolations of current partitioning models to conditions of low C-OA significantly underestimate SOA production under dark, low-NOx conditions. However, extrapolations of current models overestimate SOA production under illuminated, higher-NOx conditions typical of polluted regional air masses. C1 Carnegie Mellon Univ, Ctr Atmospher Particle Studies, Pittsburgh, PA 15213 USA.

A unified framework of semi-volatile partitioning permits models to efficiently treat both semi-volatile primary emissions and secondary organic aerosol production (SOA), and then to treat the chemical evolution (aging) of the aggregate distribution of semi-volatile material. This framework also reveals critical deficiencies in current emissions and SOA formation measurements. The key feature of this treatment is a uniform basis set of saturation vapor pressures spanning the range of ambient organic saturation concentrations, from effectively nonvolatile material at 0.01 mu g m(-3) to vapor-phase effluents at 100 mg m(-3). Chemical evolution can be treated by a transformation matrix coupling the various basis vectors. Using this framework, we show that semi-volatile partitioning can be described in a self-consistent way, with realistic behavior with respect to temperature and varying organic aerosol loading. The time evolution strongly suggests that neglected oxidation of numerous intermediate volatility vapors (IVOCs, with saturation concentrations above similar to 1 mg m(-3)) may contribute significantly to ambient SOA formation. C1 Carnegie Mellon Univ, Ctr Atmospher Particle Studies, Pittsburgh, PA 15213 USA. Univ Iowa, Dept Chem Engn, Iowa City, IA 52242 USA.

The cloud condensation nuclei (CCN) activation of 19 organic species with water solubilities (C-sat) ranging from 10(-4) to 10(2) g solute 100g(-1) H2O was measured. The organic particles were generated by nebulization of an aqueous or an alcohol solution. Use of alcohols as solvents enables the measurement of low solubility, non-volatile organic CCN activity and reduces the likelihood of residual water in the aerosol. The activation diameter of organic species with very low solubility in water (C-sat < 0.3 g 100 g(-1) H2O) is in agreement with Kohler theory using the bulk solubility (limited solubility case) of the organic in water. Many species, including 2-acetylbenzoic acid, aspartic acid, azelaic acid, glutamic acid, homophthalic acid, phthalic acid, cis-pinonic acid, and salicylic acid are highly CCN active in spite of their low solubility (0.3 g 100 g(-1) H2O < C-sat < 1 g 100 g(-1) H2O), and activate almost as if completely water soluble. The CCN activity of most species is reduced, if the particles are produced using non-aqueous solvents. The existence of the particles in a metastable state at low RH can explain the observed enhancement in CCN activity beyond the levels suggested by their solubility. (c) 2005 Elsevier Ltd. All rights reserved. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Hong Kong Univ Sci & Technol, Sch Engn, Enviornm Engn Program, Kowloon, Hong Kong, Peoples R China. Hong Kong Univ Sci & Technol, Dept Chem Engn, Kowloon, Hong Kong, Peoples R China. Univ Patras, Dept Chem Engn, Patras 26504, Greece.

[1] This paper presents evidence that condensed-phase organic compounds are significantly oxidized in regional air masses and in locations affected by regional transport, especially during the summer. The core of the paper examines a large data set of ambient organic aerosol concentrations for removal of reactive compounds relative to less-reactive compounds. The approach allows visualization of both photochemistry and mixing of emissions from multiple sources in order to differentiate between the two phenomena. The focus is on hopanes and alkenoic acids, important markers for motor vehicle and cooking emissions. Ambient data from Pittsburgh, PA and the Southeastern United States contain evidence for significant photochemical oxidation of these compounds in the summertime. There is a strong seasonal pattern in the ratio of different hopanes to elemental carbon consistent with oxidation. In addition, measurements at rural sites indicate that hopanes are severely depleted in the regional air mass during the summer. Alkenoic acids also appear to be photochemically oxidized during the summertime; however, the oxidation rate appears to be much slower than that inferred from laboratory experiments. The significance of photochemistry is supported by rudimentary calculations which indicate substantial oxidation by OH radicals and ozone on a time scale of a few days or so, comparable to time scales for regional transport. Oxidation is non-linear; therefore it represents a very substantial complication to linear source apportionment techniques such as the Chemical Mass Balance model. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem, Pittsburgh, PA 15213 USA. Florida Int Univ, Dept Civil & Environm Engn, Miami, FL 33199 USA.

[ 1] We evaluate the suitability of a three-dimensional chemical transport model ( CTM) as a tool for assessing ammonia emission inventories, calculate the improvement in CTM performance owing to recent advances in temporally varying ammonia emission estimates, and identify the observational data necessary to improve future ammonia emission estimates. We evaluate two advanced approaches to estimating the temporal variation in ammonia emissions: a process-based approach and an inverse-modeled approach. These inventories are used as inputs to a three-dimensional CTM, PMCAM(x). The model predictions of aerosol NH4+ concentration, NHx ( NHx equivalent to NH3 + NH4+) concentration, wet-deposited NH4+ mass flux, and NH4+ precipitation concentration are compared with observations. However, it should be cautioned that errors in model inputs other than the ammonia emissions may bias such comparisons. We estimate the robustness of each of these amodel-measurement comparisons as the ratio of the sensitivity to changes in emissions over the sensitivity to errors in the CTM inputs other than the ammonia emission inventory. We find the NHx concentration to be the only indicator that is sufficiently robust during all time periods. Using this as an indicator, the ammonia emission inventories with diurnal and seasonal variation improve the PMCAMx predictions in the summer and winter. In the United States, future efforts to improve the spatial and temporal accuracy of ammonia emission inventories are limited by a lack of a long-term, widespread network of highly time-resolved NHx measurements. C1 Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15217 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15217 USA. Univ Patras, Dept Chem Engn, Patras 26500, Greece. NOAA, Atmospher Sci Modeling Div, Air Resources Lab, Res Triangle Pk, NC 27711 USA. US EPA, Natl Exposure Res Lab, Res Triangle Pk, NC 27711 USA.

During the Pittsburgh Air Quality Study (PAQS) an automated semi-continuous thermal-optical transmittance (TOT) carbon analyzer was used to measure 2-4 h average particulate organic (OC) and elemental carbon (EC) concentrations from July 1, 2001 to August 13,2002. To minimize the adsorption of vapor-phase organics, the sample air was drawn through a multi-channel parallel-plate diffusion denuder placed upstream of the carbon analyzer. Particulate OC and EC in the sample air were then collected on a quartz fiber filter (QFF) mounted inside the carbon analyzer, and analyzed immediately after collection. To account for any remaining organic vapors not retained by the denuder and collected on the sampling filter (positive artifact) a dynamic blank was run every two weeks. An upper-bound estimate of volatilization induced by the presence of the denuder upstream of the sampling filter (negative artifact) was also made. A detailed description of the operating protocol and quality assurance measurements is provided. The contributions of primary and secondary organic aerosol (SOA) to particulate OC were calculated using an EC tracer method, which is codified herein. Annual average SOA accounted for 33% of particulate OC. SOA accounted for 30-40% of monthly average OC from June to November in Pittsburgh, similar to previous summertime estimates for Atlanta (Lim and Turpin 2002) and much larger than previous estimates of SOA in the Los Angeles Basin (Turpin and Huntzicke 1995). Examination of concentration dynamics suggests that multi-day formation and regional transport is an important contributor to the higher SOA contributions to OC in Pittsburgh and suggests that SOA is likely to be a particularly important contributor to particulate OC in locations that are recipients of long distance transport, such as the eastern United States. C1 Rutgers State Univ, Dept Environm Sci, New Brunswick, NJ 08901 USA. Rutgers Cooperat Extens, New Brunswick, NJ USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA.

Laboratory evidence suggests that inorganic acid seed particles may increase secondary organic aerosol yields secondary organic aerosol (SOA) through heterogeneous chemistry. Additional laboratory studies, however, report that organic acidity generated in the same photochemical process by which SOA is formed may be sufficient to catalyze these heterogeneous reactions. Understanding the interaction between inorganic acidity and SOA mass is important when evaluating emission controls to meet PM2.5 regulations. We examine semicontinuous measurements of organic carbon (OC), elemental carbon (EC), and inorganic species from the Pittsburgh Air Quality Study to determine if we can detect coupling in the variations of inorganic acidity and OC. We were not able to detect significant enhancements of SOA production due to inorganic acidity in Western Pennsylvania most of the time, but its signal might have been lost in the noise. If we assume a causal relationship between inorganic acidity and OC, reductions in OC for Western Pennsylvania that might result from drastic reductions in inorganic acidity were estimated to be 2 +/- 4% by a regression technique, and an upper bound for this geographic area was estimated to be 5 +/- 8% based on calculations from laboratory measurements. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA.

We describe the development and evaluation of a computationally efficient new multicomponent aerosol dynamics model that simulates the full aerosol size distribution and composition starting at a diameter of 0.8 nm. The model uses a recently developed ternary (sulfuric acid-ammonia-water) nucleation parameterization and a two-moment sectional algorithm, simulating both the aerosol number and mass distributions. Three chemical components, sulfate, ammonium, and non-volatile organics are simulated. The model is evaluated first against analytical solutions of the coagulation and condensation equations and then against ambient measurements from the Pittsburgh Air Quality Study. The model is able to reproduce nucleation events from their start to completion. The simulations suggest that ammonia availability controls the nucleation bursts in the northeastern US. The first stage of the nucleation event in that area is the nucleation burst with growth of neutral ultrafine particles. In a second stage, the gas phase ammonia concentration approaches zero, the nucleation burst stops and the ultrafine particles become acidic growing by condensation of sulfuric acid. The present model is thirty times faster than comparable high-resolution models of aerosol dynamics and nucleation. (c) 2005 Elsevier Ltd. All rights reserved. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Univ Patras, Dept Chem Engn, GR-26110 Patras, Greece.

In-use, fuel-based motor vehicle emission factors were determined using measurements made in a highway tunnel in Pittsburgh, Pennsylvania. Concentrations Of PM2.5 mass, CO, CO2, and NO, were measured continuously. Filter-based measurements included PM2.5 mass, organic and elemental carbon (OC and EQ, inorganic ions and metals. Fuel-based emission factors for each pollutant were calculated using a fuel-carbon balance. The weekday traffic volume and fleet composition varied in a consistent diurnal pattern with the estimated fraction of fuel consumed by heavy-duty diesel ve ' hicle (HDDV) traffic ranging from 11% to 36%. The emission rate of most species showed a significant dependence on sample period. NOx, PM2.5, EC and OC emission factors were significantly larger during the early morning, truckdominated period. Emissions of particulate metals associated with brake wear (Cu, Sb, Ba and potentially Ga) were emitted at higher rates during the rush-hour period, which is characterized by slower, stop-and-go traffic. Emission rates of crustal elements (Fe, Ca, Mg, Li), Zn and Mn were highest during the early-morning period when there was more heavytruck traffic. A seasonal shift in average OC/EC ratio for the rush-hour period was observed; fall and summer OC/EC ratios are 1.0+0.6 and 0.26+0.06, respectively. Potential causes for this shift are increased partitioning of semi-volatile organic compounds into the gas phase during the summer months and/or effects of seasonal changes in fuel formulation. Emission factors for HDDV and light-duty vehicles (LDV) classes were estimated using a linear regression of emission factor as a function of fleet composition. The extrapolated emission factors generally agree with previously published measurements, though a substantial range in published values is noted. (c) 2006 Elsevier Ltd. All rights reserved. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Dept Engn & Publ Policy, Dept Chem Engn, Pittsburgh, PA 15213 USA.

Thermal-optical analysis is a conventional method for classifying carbonaceous aerosols as organic carbon (OC) and elemental carbon (EC). This article examines the effects of three different temperature protocols on the measured EC. For analyses of parallel punches from the same ambient sample, the protocol with the highest peak helium-mode temperature (870 degrees C) gives the smallest amount of EC, while the protocol with the lowest peak helium-mode temperature (550 degrees C) gives the largest amount of EC. These differences are observed when either sample transmission or reflectance is used to define the OC/EC split. An important issue is the effect of the peak helium-mode temperature on the relative rate at which different types of carbon with different optical properties evolve from the filter. Analyses of solvent-extracted samples are used to demonstrate that high temperatures (870 degrees C) lead to premature EC evolution in the helium-mode. For samples collected in Pittsburgh, this causes the measured EC to be biased low because the attenuation coefficient of pyrolyzed carbon is consistently higher than that of EC. While this problem can be avoided by lowering the peak helium-mode temperature, analyses of wood smoke dominated ambient samples and levoglucosan-spiked filters indicate that too low helium-mode peak temperatures (550 degrees C) allow non-light absorbing carbon to slip into the oxidizing mode of the analysis. If this carbon evolves after the OC/EC split, it biases the EC measurements high. Given the complexity of ambient aerosols, there is unlikely to be a single peak helium-mode temperature at which both of these biases can be avoided. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Duke Univ, Dept Civil & Environm Engn, Durham, NC 27706 USA.

Experimental measurements of gas-particle partitioning and organic aerosol mass in diluted diesel and wood combustion exhaust are interpreted using a two-component absorptive-partitioning model. The model parameters are determined by fitting the experimental data. The changes in partitioning with dilution of both wood smoke and diesel exhaust can be described by two lumped compounds in roughly equal abundance with effective saturation concentrations of similar to 1600 mu g m(-3) and similar to 20 mu g m(-3). The model is used to investigate gas-particle partitioning of emissions across a wide range of atmospheric conditions. Under the highly dilute conditions found in the atmosphere, the partitioning of the emissions is strongly influenced by the ambient temperature and the background organic aerosol concentration. The model predicts large changes in primary organic aerosol mass with varying atmospheric conditions, indicating that it is not possible to specify a single value for the organic aerosol emissions. Since atmospheric conditions vary in both space and time, air quality models need to treat primary organic aerosol emissions as semivolatile. Dilution samplers provide useful information about organic aerosol emissions; however, the measurements can be biased relative to atmospheric conditions and constraining predictions of absorptive-partitioning models requires emissions data across the entire range of atmospherically relevant concentrations. C1 Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Univ Iowa, Dept Chem & Biochem Engn, Iowa City, IA 52242 USA.

Experiments were conducted to examine the effects of dilution on fine particle mass emissions from a diesel engine and wood stove. Filter measurements were made simultaneously using three dilution sampling systems operating at dilution ratios ranging from 20:1 to 510:1. Denuders and backup filters were used to quantify organic sampling artifacts. For the diesel engine operating at low load and wood combustion, large decreases in fine particle mass emissions were observed with increases in dilution. For example, the PM2.5 mass emission rate from a diesel engine operating at low load decreased by 50% when the dilution ratio was increased from 20:1 to 350:1. Measurements of organic and elemental carbon indicate that the changes in fine particle mass with dilution are caused by changes in partitioning of semivolatile organic compounds. At low levels of dilution semivolatile species largely occur in the particle phase, but increasing dilution reduces the concentration of semivolatile species, shifting this material to the gas phase in order to maintain phase equilibrium. Emissions of elemental carbon do not vary with dilution. Organic sampling artifacts are shown to vary with dilution because of the combination of changes in partitioning coupled with adsorption of gas-phase organics by quartz filters. The fine particle mass emissions from the diesel engine operating at medium load did not vary with dilution because of the lower emissions of semivolatile material and higher emissions of elemental carbon. To measure partitioning of semivolatile materials under atmospheric conditions, partitioning theory indicates that dilution samplers need to be operated such that the diluted exhaust achieves atmospheric levels of dilution. Too little dilution can potentially overestimate the fine particle mass emissions, and too much dilution (with clean air) can underestimate them. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA.

[1] An integrated global model of climate, tropospheric gas phase chemistry, and aerosols has been used to investigate the sensitivity of global ozone and fine particulate matter concentrations to climate change. Two simulations corresponding to present (1990s) and future ( 2050s) climates have been performed and compared. A future climate has been imposed using ocean boundary conditions corresponding to the Intergovernmental Panel on Climate Change SRES A2 scenario for the 2050s decade, resulting in an increase in the global annual average values of the surface air temperature by 1.7 degrees C, the lower tropospheric specific humidity by 0.9 g H2O/kg air, and the precipitation by 0.15 mm d(-1). Present-day anthropogenic emissions have been used in both simulations while climate-sensitive natural emissions were allowed to vary with the simulated climate. The tropospheric ozone burden in the future climate run decreased by 5%, and its lifetime decreased from 27.8 to 25.3 days. The tropospheric ozone change is driven primarily by increased ozone loss rates through ozone photolysis in the presence of water vapor, which on a global scale, more than compensate for the increased ozone chemical production associated with increased temperatures. At the model surface layer, over remote regions, ozone mixing ratios decreased by 1-3 ppbv, while polluted regions showed a relatively smaller decrease of 0-1 ppbv and increased by 1-5 ppbv in some cases. The global burdens and lifetimes of fine particulate matter species in the future climate run decreased by 2 to 18% because of increased wet deposition loss rates associated with increased precipitation. At the model surface layer, there are regions of decreases and increases in the concentrations of fine particulate matter species. The increased surface layer concentrations of some fine particulate matter species is primarily driven by lower regional-scale precipitation and increased secondary production, where applicable. The robustness of the predicted regional-scale changes for fine particulate matter species is strongly dependent upon the predicted regional-scale precipitation changes. C1 Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA.

Existing generators installed for backup during blackouts could be operated during periods of peak electricity demand, increasing grid reliability and supporting electricity delivery. Many generators, however, have non-negligible air emissions and may potentially damage air quality and harm human health. To evaluate using these generators, we compare the levelized private and social (health) costs of diesel internal combustion engines (ICE) with and without diesel particulate filters (DPF), natural gas ICEs, and microturbines to a new peaking plant in New York, NY. To estimate the social cost, first we calculate the upper range emissions for each generator option from producing 36 000 megawatt-hours (MWh) of electricity over 3 days. We then convert the emissions into ambient concentrations with a 3-D chemical transport model, PMCAM(X), and Gaussian dispersion plumes. Using a Monte Carlo approach to incorporate the uncertainties, we calculate the health endpoints using concentration-response functions and multiply the response by its economic value. While uncontrolled diesel ICEs would harm air quality and health, a generator with a DPF has a social cost, comparable to natural gas options. We conclude on a full cost basis that backup generators, including controlled diesel ICEs, are a cost-effective method of meeting peak demand. C1 Carnegie Mellon Univ, Tepper Business Sch, Pittsburgh, PA 15213 USA.

A group of twenty-four leading atmospheric and climate scientists provided subjective probability distributions that represent their current judgment about the value of planetary average direct and indirect radiative forcing from anthropogenic aerosols at the top of the atmosphere. Separate estimates were obtained for the direct aerosol effect, the semi-direct aerosol effect, cloud brightness (first aerosol indirect effect), and cloud lifetime/distribution (second aerosol indirect effect). Estimates were also obtained for total planetary average forcing at the top of the atmosphere and for surface forcing. Consensus was strongest among the experts in their assessments of the direct aerosol effect and the cloud brightness indirect effect. Forcing from the semi-direct effect was thought to be small (absolute values of all but one of the experts' best estimates were -0.5 W/m(2)). There was not agreement about the sign of the best estimate of the semi-direct effect, and the uncertainty ranges some experts gave for this effect did not overlap those given by others. All best estimates of total aerosol forcing were negative, with values ranging between -0.25 W/m(2) and -2.1 W/m(2). The range of uncertainty that a number of experts associated with their estimates, especially those for total aerosol forcing and for surface forcing, was often much larger than that suggested in 2001 by the IPCC Working Group 1 summary figure (IPCC, 2001). C1 Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Univ Calgary, Dept Chem & Petr Engn, Calgary, AB T2N 1N4, Canada. Univ Calgary, Dept Econ, Calgary, AB T2N 1N4, Canada.

[1] The contribution of both the sea-salt emissions and specifically the ultrafine (dry D-p < 0.1 mu m) component of these emissions to global CCN was assessed with a global model of aerosol microphysics. Four sea-salt emissions parameterizations were incorporated into the GISS II-prime general circulation model with the size-resolved aerosol microphysics module, TOMAS. The results of the four simulations were compared to observations of monthly average PM10 sea-salt mass, sea-salt mass size distributions, and marine aerosol number distributions. The agreement of the simulations with the observations varied greatly based on the sea-salt emissions parameterization used, but validation of the parameterizations is limited by uncertainty in the model's wind speeds. The impact of sea-salt aerosols on CCN concentrations was assessed by looking at the percent change in CCN(0.2%) concentrations between a simulation including both sea salt and sulfate and a simulation including sulfate alone. Two of the emissions parameterizations included ultrafine sea-salt particles, and the contribution of the ultrafine particles to CCN( 0.2%) formation was assessed by sensitivity studies. Depending on the emissions estimate used, the addition of sea salt increased CCN( 0.2%) over the Southern Ocean by 150% to 500%. The highest increases resulted from the simulations that included ultrafine emissions where it was found that the ultrafine sea salt can increase CCN( 0.2%) concentrations over both the Southern Ocean and Antarctica by more than 50% relative to the same parameterizations with ultrafine sea salt excluded. The sensitivity of CCN( 0.2%) to ultrafine sea-salt emissions enhances the importance of reducing the uncertainty of sea-salt emissions parameterizations and their subsequent treatment in aerosol models. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA.

During the Pittsburgh Air Quality Study (PAQS), July 2001-September 2002, three co-located instruments analyzed the composition of ambient particulate matter (PM): (1) A single particle mass spectrometer, RSMS-3, was deployed to obtain high-temporal-resolution measurements of single particle size (> 1.1 mu m) and composition which were correlated with meteorological data to identify sources; (2) PM2.5 and PM10 were collected on cellulose filters using high-volume (hi-vol) samplers, followed by microwave-assisted digestion and analysis by inductively coupled plasma-mass spectrometry (ICP-MS). Positive matrix factorization (PMF) was used to identify possible source categories; and (3) a micro-orifice uniform-deposit impactor (MOUDI) obtained size-distributed samples of PM. Several days of MOUDI filters were selected for microwave-assisted digestion and analysis by ICP-MS. In this paper, sources identified using the single particle data were compared to the PMF results for the hi-vol/ICP-MS data. The strengths of each method were combined to hypothesize the most likely sources of various elements in ambient PM in Pittsburgh. In the final results, Mo and Cr are attributed to local specialty steel facilities; Fe, Mn, Zn, and K are attributed to a steel mill SE of the monitoring station; internally mixed Pb-containing particles are attributed to a major source to the NW; and Ga is attributed to coal combustion sources to the NW. There is a notable lack of oil combustion sources. The MOUDI data were used to resolve discrepancies between the single particle and hi-vol/ICP-MS data concerning the detection of Ti and Se. The hi-vol data showed appreciable Ti and Se masses, but RSMS-3 was unable to detect significant numbers of Ti-containing particles because of their large size, while we hypothesize that the volatility of Se caused it to be distributed more evenly over all emitted particles such that the amount of Se in any individual particle is below the limit of detection. (c) 2006 Elsevier Ltd. All rights reserved. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Univ Calif Davis, Dept Land Air & Water Resources, Davis, CA 95616 USA. Univ Calif Davis, Dept Mech & Aeronaut Engn, Davis, CA 95616 USA. Univ Delaware, Dept Chem & Biochem, Newark, DE 19716 USA.

A single particle mass spectrometer, RSMS-3, and a MOUDI were deployed during the Pittsburgh Air Quality Study (PAQS), July 2001-September 2002, to obtain size resolved measurements of elemental composition for particulate matter (PM) within the Pittsburgh area. Elemental mass distributions from analysis of the MOUDI stages were directly compared to those constructed using the single particle data, in conjunction with coincident SMPS measurements, for specific days within the PAQS. Results from one episode on 27 October 2001 showed that approximately 80% of the metal containing particles detected on this day belonged to the Na/Si/K/Ca/Fe/Ga/Pb particle class. The density and shape factor of these particles were estimated to be 3.9 +/- 0.8 g/cc and 1.5 +/- 0.2, respectively, and the relative sensitivity factors for individual metals showed little variation with respect to particle diameter over the size range of 70-800 nm. Compared to the 27 October 2001 episode, there was a larger degree of variability in the metal containing particles detected during another episode on 14 March 2002. The Ca and Pb mass distributions from this day represent an ensemble of externally mixed particles. Estimates of particle density were provided for the dominant particle types, including EC/OC/Ca, Al/Si/Ca/Fe, EC/OC/Pb and Na/K/Zn/Pb, and estimates of particle shape factor were provided for the EC/OC/Ca and Na/K/Zn/Pb classes. Comparison with the 27 October 2001 Ca and Pb mass distributions revealed that the RSMS data reconstructed the MOUDI mass much better from the Ca/Pb containing particles detected on 14 March 2002 than those observed on 27 October 2001, suggesting that the single particle instrument sensitivity to both Ca and Pb depends on the particle matrix. (c) 2006 Elsevier Ltd. All rights reserved. C1 Univ Calif Davis, Dept Land Air & Water Resources, Davis, CA 95616 USA. Univ Calif Davis, Dept Mech & Aeronaut Engn, Davis, CA 95616 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Publ Policy, Pittsburgh, PA 15213 USA. Univ Delaware, Dept Chem & Biochem, Newark, DE 19716 USA. Univ Calif Davis, Dept Mech & Aeronaut Engn, Davis, CA 95616 USA.

Apportionment of primary and secondary pollutants during the summer 2001 Pittsburgh Air Quality Study (PAQS) is reported. Several sites were included in PAQS, with the main site (the supersite) adjacent to the Carnegie Mellon University campus in Schenley Park. One of the additional sampling sites was located at the National Energy Technology Laboratory, located similar to 18 km southeast of downtown Pittsburgh. Fine particulate matter (PM2.5) mass, gas-phase volatile organic material (VOM), particulate semivolatile and nonvolatile organic material (NVOM), and ammonium sulfate were apportioned at the two sites into their primary and secondary contributions using the U.S. Environmental Protection Agency UNMIX 2.3 multivariate receptor modeling and analysis software. A portion of each of these species was identified as originating from gasoline and diesel primary mobile sources. Some of the organic material was formed from local secondary transformation processes, whereas the great majority of the secondary sulfate was associated with regional transformation contributions. The results indicated that the diurnal patterns of secondary gas-phase VOM and particulate semivolatile and NVOM were not correlated with secondary ammonium sulfate contributions but were associated with separate formation pathways. These findings are consistent with the bulk of the secondary ammonium sulfate in the Pittsburgh area being the result of contributions from distant transport and, thus, decoupled from local activity involving organic pollutants in the metropolitan area. C1 Brigham Young Univ, Dept Chem & Biochem, Provo, UT 84662 USA. US DOE, Natl Energy Technol Lab, Pittsburgh, PA USA. Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Brigham Young Univ, Dept Chem & Biochem, Provo, UT 84602 USA.

An objective of the Pittsburgh Air Quality Study was to determine the major sources Of PM2.5 in the Pittsburgh region. Daily 24-hour averaged filter-based data were collected for 13 months, starting in July 2001, including sulfate and nitrate data from IC analysis, trace element data from ICP-MS analysis, and organic and elemental carbon from the thermal optical transmittance (TOT) method and the NIOSH thermal evolution protocol. These data were used in two source-receptor models, Unmix and PMF. Unmix, which is limited to a maximum number of seven factors, resolved six source factors, including crustal material, a regional transport factor, secondary nitrate, an iron, zinc and manganese factor, specialty steel production and processing, and cadmium. PMF, which has no limit to the number of factors, apportioned the PM2.5 mass into ten factors, including crustal material, secondary sulfate, primary OC and EC, secondary nitrate, an iron, zinc and manganese factor, specialty steel production and processing, cadmium, selenium, lead, and a gallium-rich factor. The Unmix and PMF common factors agree reasonably well, both in composition and contributions to PM2.5. To further identify and apportion the sources Of PM2.5, specific OC compounds that are known markers of some sources were added to the PMF analysis. The results were similar to the original solution, except that the primary OC and EC factor split into two factors. One factor was associated with vehicles as identified by the hopanes, PAH's, and other OC compounds. The other factor had strong correlations with the OC and EC ambient data as well as wood smoke markers such as levoglucosan, syringols, and resin acids. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn & Engn & Publ Policy, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Mech Engn & Engn & Publ Policy, Pittsburgh, PA 15213 USA. Clarkson Univ, Ctr Air Resources Engn & Sci, Potsdam, NY USA. Clarkson Univ, Dept Chem Engn, Potsdam, NY USA. Brigham Young Univ, Dept Chem & Biochem, Provo, UT 84602 USA. Florida Int Univ, Ctr Engn, Dept Civil & Environm Engn, Miami, FL 33199 USA.

Ambient PM2.5 composition. data in Pittsburgh, PA have been used with Positive Matrix Factorization (PMF) to determine the major sources of PM2.5 sampled. This paper describes the use of the potential source contribution function (PSCF) with the PMF-modeled source contributions to locate. the sources in a. grid of 0.1 degrees x 0.1 degrees cells. The domain extends from the Pittsburgh Supersite at 40.40 degrees N, 79.94 degrees W over the range 35 degrees-50 degrees north, latitude and 75 degrees-90 degrees west longitude. Six-hour back trajectories have been obtained from HYSPLIT four times each day for the 13 months of the study for use with PSCE Using the results, higher probability locations are compared with known, locations of specific source types, based on information from the EPA Toxic Release Inventory (TRI) and the EPA AIRS Database. PSCF results for several sources are compared to the conditional probability function (CPF) analysis, which uses 15-minute wind direction data to determine the most probable direction of a source. Using PSCF and CPF together aids in interpretation of potential source regions. The selenium and sulfate factor source locations are regional, while the lead, cadmium, and. specialty steel factor source, locations are local. The gallium-rich and Fe Mn, and Zn factor source locations are potentially both local and regional. The nitrate, vehicle emissions and road dust, wood combustion, vegetative detritus and cooking, and crustal material factor CPF and: PSCF results were inconclusive as sources of these. factors exist. in all directions fro m the site and therefore one would not expect a clear probability field in any one direction. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Civil & Environm Engn & Engn & Publ Policy, Pittsburgh, PA 15213 USA. Clarkson Univ, Ctr Air Resources Engn & Sci, Potsdam, NY USA. Clarkson Univ, Dept Chem Engn, Potsdam, NY USA.

Estimates for the air releases of lead from stationary point sources are considered for the South Coast Air Basin of California. We have examined four databases published by U.S. Environmental Protection Agency, the California Air Resources Board, and the South Coast Air Quality Management District. Our analysis indicates that none of the databases includes every emitting facility in the South Coast Air Basin of California and that other discrepancies among the databases exist. Additionally, the data have been analyzed for temporal variation, and some of the California Air Resources Board data are not current. The South Coast Air Quality Management District inventory covers 12 times more facilities in 2001 than in 1996. From this analysis, we conclude that all four of the databases would benefit by sharing data, increasing transparency, analyzing uncertainty, and standardizing emission estimation methods. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA USA. WinTec Inc, Ft Washington, MD USA.