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Atmospheric ammonia (NH3) can affect nitrogen deposition, particle acidity, and gas-particle partitioning. Although the inorganic chemistry of NH3 in fine particulate (PM2.5) formation are well-constrained, the understanding of interactions between NH3 and secondary organic aerosol (SOA) are rather insufficient until recently. Laboratory studies indicate that NH3 molecule can react with SOA then forms nitrogen-containing organic compounds (NOCs), which can further react to form heterocyclic organic compounds. In this study, we use a modified version of the CMAQ model to simulate the potential importance of the SOA-ammonia uptake mechanism on air quality over China in summer and winter 2017, considering a range of assumed NH3 uptake coefficients (10−3–10−5). Our results show that uptake of NH3 by SOA leads to a decrease in gas-phase NH3 mixing ratio, by as much as 27.5% and 19.0% for the highest uptake coefficient scenario (10−3) in summer and winter, respectively. The largest reduction of ammonia occurs over the Sichuan Basin and the North China Plain. The reduction of gas-phase NH3 engenders a decrease of ammonium nitrate, by up to 30%, but has little impact on the ammonium sulfate concentration. Uptake of NH3 does not significantly affect SOA concentrations owing to overall moderate changes in aerosol acidity, and thus small effects on SOA formation from isoprene. Altogether, NH3 uptake led to a reduction in the average PM2.5 concentration up to 8.9% and 8.7% for the highest uptake coefficient (10−3) in summer and winter, respectively. These results highlight the need for better constraints on the NH3-SOA interactions.

The effect of relative humidity (RH) on the chemical composition of secondary organic aerosol (SOA) formed from low-NOx toluene oxidation in the absence of seed particles was investigated. SOA samples were prepared in an aerosol smog chamber at >2%RH and 75%RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI-HRMS). Measurements revealed a significant reduction in the fraction of oligomers present in the SOA generated at 75%RH compared to SOA generated under dry conditions. In a separate set of experiments, the particle mass concentrations were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from >2 to 90 %. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from >2 to 75-90% for low-NOx toluene SOA. The volatility distributions of the SOA compounds, estimated from the distribution of molecular formulas using the "molecular corridor" approach, confirmed that low-NOx toluene SOA became more volatile on average under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NOx toluene SOA. The observed increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compounds in low-NOx toluene SOA. The reduction in the fraction of oligomeric compounds under humid conditions is predicted to partly counteract the previously observed enhancement in the toluene SOA yield driven by the aerosol liquid water chemistry in deliquesced inorganic seed particles.

The introduction of fuel cell electric vehicles (FCEV) operating on hydrogen is a key strategy to mitigate pollutant emissions from the light duty vehicle (LDV) transportation sector in pursuit of air quality (AQ) improvements. Further, concomitant increases in renewable power generation could assist in achieving benefits via electrolysis-provided hydrogen as a vehicle fuel. However, it is unclear (1) reductions in emissions translate to changes in primary and secondary pollutant concentrations and (2) how effects compare to those from emissions in other transport sectors including heavy duty vehicles (HDV). This work assesses how the adoption of FCEVs in counties expected to support alternative LDV technologies affect atmospheric concentrations of ozone and fine particulate matter (PM2.5) throughout California (CA) in the year 2055 relative to a gasoline vehicle baseline. Further, impacts of reducing HDV emissions are explored to facilitate comparison among technology classes. A base year emissions inventory is grown to 2055 representing a business-as-usual progression of economic sectors, including primarily petroleum fuel consumption by LDV and HDVs. Emissions are spatially and temporally resolved and used in simulations of atmospheric chemistry and transport to evaluate distributions of primary and secondary pollutants respective to baseline. Results indicate that light-duty FCEV Cases achieve significant reductions in ozone and PM2.5 when LDV market shares reach 50–100% in early adoption counties, including areas distant from deployment sites. Reflecting a cleaner LDV baseline fleet in 2055, emissions from HDVs impact ozone and PM2.5 at comparable or greater levels than light duty FCEVs. Additionally, the importance of emissions from petroleum fuel infrastructure (PFI) activity is demonstrated in impacts on ozone and PM2.5 burdens, with large refinery complexes representing a key source of air pollution in 2055. Results presented provide insight into light duty FCEV deployment strategies that can achieve maximum reductions in ozone and PM2.5 and will assist decision makers in developing effective transportation sector AQ mitigation strategies.

In this paper, the Spatially and Temporally Resolved Energy and Environment Tool (STREET) is used in conjunction with University of California Irvine - California Institute of Technology (UCI-CIT) atmospheric chemistry and transport model to assess the impact of deploying plug-in electric vehicles and integrating wind energy into the electricity grid on urban air quality. STREET is used to generate emissions profiles associated with transportation and power generation sectors for different future cases. These profiles are then used as inputs to UCI-CIT to assess the impact of each case on urban air quality. The results show an overall improvement in 8-h averaged ozone and 24-h averaged particulate matter concentrations in the South Coast Air Basin (SoCAB) with localized increases in some cases. The most significant reductions occur northeast of the region where baseline concentrations are highest (up to 6 ppb decrease in 8-h-averaged ozone and 6 μg/m3 decrease in 24-h-averaged PM2.5). The results also indicate that, without integration of wind energy into the electricity grid, the temporal vehicle charging profile has very little to no effect on urban air quality. With the addition of wind energy to the grid mix, improvement in air quality is observed while charging at off-peak hours compared to the business as usual scenario.

Sulfuric acid (H2SO4), formed from oxidation of sulfur dioxide (SO2) emitted during fossil fuel combustion, is a major precursor of new airborne particles, which have well-documented detrimental effects on health, air quality, and climate. Another precursor is methanesulfonic acid (MSA), produced simultaneously with SO2 during the atmospheric oxidation of organosulfur compounds (OSCs), such as dimethyl sulfide. In the present work, a multidisciplinary approach is used to examine how contributions of H2SO4 and MSA to particle formation will change in a large coastal urban area as anthropogenic fossil fuel emissions of SO2 decline. The 3-dimensional University of California Irvine-California Institute of Technology airshed model is used to compare atmospheric concentrations of gas phase MSA, H2SO4, and SO2 under current emissions of fossil fuel-associated SO2 and a best-case futuristic scenario with zero fossil fuel sulfur emissions. Model additions include results from (i) quantum chemical calculations that clarify the previously uncertain gas phase mechanism of formation of MSA and (ii) a combination of published and experimental estimates of OSC emissions, such as those from marine, agricultural, and urban processes, which include pet waste and human breath. Results show that in the zero anthropogenic SO2 emissions case, particle formation potential from H2SO4 will drop by about two orders of magnitude compared with the current situation. However, particles will continue to be generated from the oxidation of natural and anthropogenic sources of OSCs, with contributions from MSA and H2SO4 of a similar order of magnitude. This could be particularly important in agricultural areas where there are significant sources of OSCs.

The effects of liquefied natural gas (LNG) on pollutant emission inventories and air quality in the South Coast Air Basin (SoCAB) of California are evaluated using recent appliance emissions measurements by Lawrence Berkeley National Laboratory and the Southern California Gas Company (SoCalGas), and use of a state-of-the-art air quality model. Pollutant emissions can be impacted by LNG operation because of differences in composition and physical properties including the Wobbe index, a measure of energy delivery rate. Various LNG distribution scenarios are evaluated to determine the potential impacts of LNG. Projected penetration of LNG in the SoCalGas pipeline network in SoCAB is expected to be limited, which could cause increases in overall (area-wide) emissions of nitrogen oxides that are smaller than 0.05%. Based on the photochemical state of the South Coast Air Basin of California, any increase in NOx is expected to cause an increase in the highest local ozone concentrations, which is observed in model results. However, the magnitude of NOx emissions increases due to LNG use is determined to be within the uncertainty range of natural gas combustion sources and would not be discernible with the existing monitoring network.

The CalNex 2010 (California Research at the Nexus of Air Quality and Climate Change) study was designed to evaluate the chemical composition of air masses over key source regions in California. During May to June 2010, air samples were collected on board a National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft over the South Coast Air Basin of California (SoCAB) and the Central Valley (CV). This paper analyzes six effective greenhouse gases - chlorodifluoromethane (HCFC-22), 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1-difluoroethane (HCFC-142b), 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124), 1,1,1,2- tetrafluoroethane (HFC-134a), and 1,1-difluoroethane (HFC-152a) - providing the most comprehensive characterization of chlorofluorocarbon (CFC) replacement compound emissions in California. Concentrations of measured HCFCs and HFCs are enhanced greatly throughout the SoCAB and CV, with highest levels observed in the SoCAB: 310 ± 92 pptv for HCFC-22, 30.7 ± 18.6 pptv for HCFC-141b, 22.9 ± 2.0 pptv for HCFC-142b, 4.86 ± 2.56 pptv for HCFC-124, 109 ± 46.4 pptv for HFC-134a, and 91.2 ± 63.9 pptv for HFC-152a. Annual emission rates are estimated for all six compounds in the SoCAB using the measured halocarbon to carbon monoxide (CO) mixing ratios and CO emissions inventories. Emission rates of 3.05 ± 0.70 Gg for HCFC-22, 0.27 ± 0.07 Gg for HCFC-141b, 0.06 ± 0.01 Gg for HCFC-142b, 0.11 ± 0.03 Gg for HCFC-124, 1.89 ± 0.43 Gg for HFC-134a, and 1.94 ± 0.45 Gg for HFC-152b for the year 2010 are calculated for the SoCAB. These emissions are extrapolated from the SoCAB region to the state of California using population data. Results from this study provide a baseline emission rate that will help future studies determine if HCFC and HFC mitigation strategies are successful. Key PointsHCFC and HFC emissions are calculated for the year 2010 for the SoCABEmissions are extrapolated to the state of CaliforniaEmissions are calculated using CalNex field measurements © 2013. American Geophysical Union. All Rights Reserved.

Airborne particles play critical roles in air quality, health effects, visibility, and climate. Secondary organic aerosols (SOA) formed from oxidation of organic gases such as α-pinene account for a significant portion of total airborne particle mass. Current atmospheric models typically incorporate the assumption that SOA mass is a liquid into which semivolatile organic compounds undergo instantaneous equilibrium partitioning to grow the particles into the size range important for light scattering and cloud condensation nuclei activity. We report studies of particles from the oxidation of α-pinene by ozone and NO3 radicals at room temperature. SOA is primarily formed from low-volatility ozonolysis products, with a small contribution from higher volatility organic nitrates from the NO3 reaction. Contrary to expectations, the particulate nitrate concentration is not consistent with equilibrium partitioning between the gas phase and a liquid particle. Rather the fraction of organic nitrates in the particles is only explained by irreversible, kinetically determined uptake of the nitrates on existing particles, with an uptake coefficient that is 1.6% of that for the ozonolysis products. If the nonequilibrium particle formation and growth observed in this atmospherically important system is a general phenomenon in the atmosphere, aerosol models may need to be reformulated. The reformulation of aerosol models could impact the predicted evolution of SOA in the atmosphere both outdoors and indoors, its role in heterogeneous chemistry, its projected impacts on air quality, visibility, and climate, and hence the development of reliable control strategies.

Distributed power generation-electricity generation that is produced by many small stationary power generators distributed throughout an urban air basin-has the potential to supply a significant portion of electricity in future years. As a result, distributed generation may lead to increased pollutant emissions within an urban air basin, which could adversely affect air quality. However, the use of combined heating and power with distributed generation may reduce the energy consumption for space heating and air conditioning, resulting in a net decrease of pollutant and greenhouse gas emissions. This work used a systematic approach based on land-use geographical information system data to determine the spatial and temporal distribution of distributed generation emissions in the San Joaquin Valley Air Basin of California and simulated the potential air quality impacts using state-of-the-art three-dimensional computer models. The evaluation of the potential market penetration of distributed generation focuses on the year 2023. In general, the air quality impacts of distributed generation were found to be small due to the restrictive 2007 California Air Resources Board air emission standards applied to all distributed generation units and due to the use of combined heating and power. Results suggest that if distributed generation units were allowed to emit at the current Best Available Control Technology standards (which are less restrictive than the 2007 California Air Resources Board standards), air quality impacts of distributed generation could compromise compliance with the federal 8-hr average ozone standard in the region.

A transition from gasoline internal combustion engine vehicles to hydrogen fuel cell electric vehicles (FCEVs) is likely to emerge as a major component of the strategy to meet future greenhouse gas reduction, air quality, fuel independence, and energy security goals. Advanced infrastructure planning can minimize the cost of hydrogen infrastructure while assuring that energy and environment benefits are achieved. This study presents a comprehensive advanced planning methodology for the deployment of hydrogen infrastructure, and applies the methodology to delineate fully built-out infrastructure strategies, assess the associated energy and environment impacts, facilitate the identification of an optimal infrastructure roll-out strategy, and identify the potential for renewable hydrogen feedstocks. The South Coast Air Basin of California, targeted by automobile manufacturers for the first regional commercial deployment of FCEVs, is the focus for the study. The following insights result from the application of the methodology:Compared to current gasoline stations, only 11%-14% of the number of hydrogen fueling stations can provide comparable accessibility to drivers in a targeted region.To meet reasonable capacity demand for hydrogen fueling, approximately 30% the number of hydrogen stations are required compared to current gasoline stations.Replacing gasoline vehicles with hydrogen FCEVs has the potential to (1) reduce the emission of greenhouse gases by more than 80%, reduce energy requirements by 42%, and virtually eliminate petroleum consumption from the passenger vehicle sector, and (2) significantly reduce urban concentrations of ozone and PM2.5.Existing sources of biomethane in the California South Coast Air Basin can provide up to 30% of the hydrogen fueling demand for a fully built-out hydrogen FCEV scenario.A step-wise transition of judiciously located existing gasoline stations to dispense and accommodate the increasing demand for hydrogen addresses proactively key infrastructure deployment challenges including a viable business model, zoning, permitting, and public acceptance. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The combined sea port of Los Angeles and Long Beach in California constitutes the second busiest port in the United States by shipping volume. Communities near the ports face environmental justice concerns from a variety of sources including roadway and port related activities. This study examines the transport and diffusion of PM2.5 and NOX in port communities using the high-resolution plume model AERMOD, incorporating surface and aloft observed meteorology and local topography. Pollution impacts of roadway related emissions, direct port activity of cargo handling equipment and commercial shipping vessels are modeled for representative cold and hot months in 2005. Predictions from roadway emissions are compared with the same episode modeled with CALINE4 line dispersion model. Results show high spatial variability as well as increased transport during cold months. In addition, research also shows that while the port activity significantly impacts in-port air pollution, the effects of port activity is limited to within 2-6 km of the ports. Port adjacent communities are most sensitive to roadway related emissions. AERMOD PM2.5 and NOX predictions show a peak correlation coefficient of 43% and 50% compared with observations, respectively. (c) Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License.

This study assesses the air quality impacts of central power generation and compares them with the impacts of distributed generation (DG). The central power plant emissions factors used are from a newly installed combined cycle gas turbine system. Because location of power plants is a key parameter affecting air quality impacts, this study considers three potential locations for the installation of central power plants. Air quality impacts are evaluated for the South Coast Air Basin of California, in the year 2010, using a three-dimensional air quality model. Results are compared to air quality impacts from two potential DG scenarios to meet the same power demand as that of the central power plant case.Even though emissions from central generation are lower than emissions from the DG technology mix considered herein, central generation concentrates emissions in a small area, whereas DG spreads emissions throughout a larger cross-section of the air basin. As a result, air quality impacts from central generation are more significant than those from DG. The study also shows that assessment of air quality impacts from distributed and central generation should not only consider emissions levels, but also the spatial and temporal distribution of emissions and the air quality that results from atmospheric chemistry and transport - highly non-linear processes.Finally, analysis of population exposure to ozone and PM2.5 shows that central generation located in coastal areas upwind from populated areas would cause the highest population exposure and even though emissions from central generation are considerably lower than DG emissions spread throughout the basin, results show that central generation causes a higher pollutant exposure than DG. © 2010 Elsevier Ltd.

Adoption of hydrogen infrastructure and hydrogen fuel cell vehicles (HFCVs) to replace gasoline internal combustion engine (ICE) vehicles has been proposed as a strategy to reduce criteria pollutant and greenhouse gas (GHG) emissions from the transportation sector and transition to fuel independence. However, it is uncertain (1) to what degree the reduction in criteria pollutants will impact urban air quality, and (2) how the reductions in pollutant emissions and concomitant urban air quality impacts compare to ultralow emission gasoline-powered vehicles projected for a future year (e.g., 2060). To address these questions, the present study introduces a "spatially and temporally resolved energy and environment tool" (STREET) to characterize the pollutant and GHG emissions associated with a comprehensive hydrogen supply infrastructure and HFCVs at a high level of geographic and temporal resolution. To demonstrate the utility of STREET, two spatially and temporally resolved scenarios for hydrogen infrastructure are evaluated in a prototypical urban airshed (the South Coast Air Basin of California) using geographic information systems (GIS) data. The well-to-wheels (WTW) GHG emissions are quantified and the air quality is established using a detailed atmospheric chemistry and transport model followed by a comparison to a future gasoline scenario comprised of advanced ICE vehicles. One hydrogen scenario includes more renewable primary energy sources for hydrogen generation and the other includes more fossil fuel sources. The two scenarios encompass a variety of hydrogen generation, distribution, and fueling strategies. GHG emissions reductions range from 61 to 68% for both hydrogen scenarios in parallel with substantial improvements in urban air quality (e.g., reductions of 10 ppb in peak 8-h-averaged ozone and 6 mug/m(3) in 24-h-averaged particulate matter concentrations, particularly in regions of the airshed where concentrations are highest for the gasoline scenario).

Gaseous HCl generated from a variety of sources is ubiquitous in both outdoor and indoor air. Oxides of nitrogen (NO(y)) are also globally distributed, because NO formed in combustion processes is oxidized to NO(2), HNO(3), N(2)O(5) and a variety of other nitrogen oxides during transport. Deposition of HCl and NO(y) onto surfaces is commonly regarded as providing permanent removal mechanisms. However, we show here a new surface-mediated coupling of nitrogen oxide and halogen activation cycles in which uptake of gaseous NO(2) or N(2)O(5) on solid substrates generates adsorbed intermediates that react with HCl to generate gaseous nitrosyl chloride (ClNO) and nitryl chloride (ClNO(2)), respectively. These are potentially harmful gases that photolyze to form highly reactive chlorine atoms. The reactions are shown both experimentally and theoretically to be enhanced by water, a surprising result given the availability of competing hydrolysis reaction pathways. Airshed modeling incorporating HCl generated from sea salt shows that in coastal urban regions, this heterogeneous chemistry increases surface-level ozone, a criteria air pollutant, greenhouse gas and source of atmospheric oxidants. In addition, it may contribute to recently measured high levels of ClNO(2) in the polluted coastal marine boundary layer. This work also suggests the potential for chlorine atom chemistry to occur indoors where significant concentrations of oxides of nitrogen and HCl coexist.

A sampling campaign was conducted in the city of Milan, Italy before and during a transportation strike in January 2004. This strike provided a unique opportunity to investigate the influence of public transportation on the air quality in a major metropolitan area. Twenty-four air samples were collected each day around the city on January 2nd, 7th and 9th. The samples were analyzed for methane, carbon monoxide, non-methane hydrocarbons (NMHCs), halocarbons and alkyl nitrates. Significant differences in the mixing ratios were observed among the three days of sampling, with January 2nd showing the lowest concentrations as a result of decreased activity in the city during the holiday season. January 9th showed the highest NMHC concentrations because of increased vehicular activity in the city due to a public transportation strike. This paper investigates the correlation between the increased number of vehicles and decreased air quality because of a reduction in public transportation. Computer simulations were able to reproduce measurements of ozone production during the January 2004 strike and a July 2005 strike. The measurements and simulations suggest that reduced VOC emissions due to the existence of public transportation lowers peak ozone by 11-33% during the summer months. © 2008 Elsevier Ltd. All rights reserved.

Emissions from the potential installation of distributed energy resources (DER) in the place of current utility-scale power generators have been introduced into an emissions inventory of the northeastern United States. A methodology for predicting future market penetration of DER that considers economics and emission factors was used to estimate the most likely implementation of DER. The methodology results in spatially and temporally resolved emission profiles of criteria pollutants that are subsequently introduced into a detailed atmospheric chemistry and transport model of the region. The DER technology determined by the methodology includes 62% reciprocating engines, 34% gas turbines, and 4% fuel cells and other emerging technologies. The introduction of DER leads to retirement of 2625 MW of existing power plants for which emissions are removed from the inventory. The air quality model predicts maximum differences in air pollutant concentrations that are located downwind from the central power plants that were removed from the domain. Maximum decreases in hourly peak ozone concentrations due to DER use are 10 ppb and are located over the state of New Jersey. Maximum decreases in 24-hr average fine particulate matter (PM2.5) concentrations reach 3 microg/m3 and are located off the coast of New Jersey and New York. The main contribution to decreased PM2.5 is the reduction of sulfate levels due to significant reductions in direct emissions of sulfur oxides (SO(x)) from the DER compared with the central power plants removed. The scenario presented here represents an accelerated DER penetration case with aggressive emission reductions due to removal of highly emitting power plants. Such scenario provides an upper bound for air quality benefits of DER implementation scenarios.

The implementation of Distributed Generation (DG) may lead to increased pollutant emissions that adversely affect air quality. This work presents a systematic methodology to characterise DG installation in urban basins. First, a set of parameters that characterise a DG implementation scenario is described. Second, a general approach using Geographic Information Systems (GIS) data is presented. Third, the methodology is demonstrated by application to the South Coast Air Basin (SoCAB) of California. Results show that realistic scenarios in the SoCAB concentrate DG technologies nearby industrial zones and introduce pollutant mass increments no larger than 0.43% with respect to baseline emissions. © 2008 Inderscience Enterprises Ltd.

While there is increasing evidence for unique chemical reactions at interfaces, there are fewer data on photochemistry at liquid-vapor junctions. This paper reports a comparison of the photolysis of molybdenum hexacarbonyl, Mo(CO)(6), in 1-decene either as liquid droplets or in bulk-liquid solutions. Mo(CO)(6) photolysis is faster by at least three orders of magnitude in the aerosols than in bulk-liquids. Two possible sources of this enhancement are considered: (1) increased light intensity due to either Morphology-Dependent Resonances (MDRs) in the spherical aerosol particles and/or to increased pathlengths for light inside the droplet due to refraction, which are termed physical effects in this paper; and (2) interface effects such as an incomplete solvent-cage at the gas-liquid boundary and/or enhanced interfacial concentrations of Mo(CO)(6), which are termed chemical effects. Quantitative calculations of the first possibility were carried out in which the light intensity distribution in the droplets averaged over 215-360 nm was obtained for 1-decene droplets. Calculations show that the average increase in light intensity over the entire droplet is 106%, with an average increase of 51% at the interface. These increases are much smaller than the observed increase in the apparent photolysis rate of droplets compared to the bulk. Thus, chemical effects, i.e., a decreased solvent-cage effect at the interface and/or enhancement in the surface concentration of Mo(CO)(6), are most likely responsible for the dramatic increase in the photolysis rate. Similar calculations were also carried out for broadband (290-600 nm) solar irradiation of water droplets, relevant to atmospheric conditions. These calculations show that, in agreement with previous calculations by Mayer and Madronich [B. Mayer and S. Madronich, Atmos. Chem. Phys., 2004, 4, 2241] MDRs produce only a moderate average intensity enhancement relative to the corresponding bulk-liquid slabs when averaged over a range of wavelengths characteristic of solar radiation at the Earth's surface. However, as in the case of Mo(CO)(6) in 1-decene, chemical effects may play a role in enhanced photochemistry at the aerosol-air interface for airborne particles.

This study evaluates air quality model sensitivity to input and to model components. Simulations are performed using the California Institute of Technology (CIT) airshed model. Results show the impacts on ozone (O3) concentration in the South Coast Air Basin (SCAB) of California because of changes in: (1) input data, including meteorological conditions (temperature, UV radiation, mixing height, and wind speed), boundary conditions, and initial conditions (ICs); and (2) model components, including advection solver and chemical mechanism. O3 concentrations are strongly affected by meteorological conditions and, in particular, by temperature. ICs also affect O3 concentrations, especially in the first 2 days of simulation. On the other hand, boundary conditions do not significantly affect the absolute peak O3 concentration, although they do affect concentrations near the inflow boundaries. Moreover, predicted O3 concentrations are impacted considerably by the chemical mechanism. In addition, dispersion of pollutants is affected by the advection routine used to calculate its transport. Comparison among CIT, California Photochemical Grid Model (CALGRID), and Urban Airshed Model air quality models suggests that differences in O3 predictions are mainly caused by the different chemical mechanisms used. Additionally, advection solvers contribute to the differences observed among model predictions. Uncertainty in predicted peak O3 concentration suggests that air quality evaluation should not be based solely on this single value but also on trends predicted by air quality models using a number of chemical mechanisms and with an advection solver that is mass conservative.

Distributed Energy Resources (DER) have the potential to meet a significant portion of increased power demands of the future. DER applications can potentially provide benefits in electrical reliability and power quality, in addition to reducing total energy costs in combined cooling, heating and power (CHP) applications. However, the shift from a central generation paradigm to distributed generation results in different emissions characteristics and profiles from both a spatial and temporal perspective. Distributed generation is characterized by many sparsely distributed stationary sources within an urban air-shed compared to central generation where emissions sources are much larger, but typically located outside the air-shed in more remote locations. As a result, high market adoption of fuel-driven (non-renewable) distributed generation (DG) technologies, such as reciprocating engines and microturbines, may influence the air quality within a region. The present paper estimates air quality impacts for a representative distributed generation scenario in the South Coast Air Basin (SoCAB) of California. Simulations are based on the year 2010 with comparison to a base case scenario with no DG emissions. The DG scenarios are developed for a reasonable percentage of power met by DG, representative spatial distribution and temporal operation, and a mix of DG technologies and emissions factors. The resultant emissions inventory for each DG scenario is then provided as input to a three-dimensional air quality model including detailed atmospheric chemistry and transport for simulation of the SoCAB. Preliminary air quality results suggest that there will be an air quality impact, that the impacts will not be uniform throughout the air-shed, and that individual criteria pollutant concentrations may either rise or fall with the introduction of DG.