Is tree growth reduction related to direct foliar injuries or soil chemistry modifications?

In the context of intense emissions causing atmospheric pollution, tree growth reductions could be related to soil chemistry modifications or direct foliar injuries. To verify these hypotheses, mineral soils were sampled in an area (Murdochville, Canada) where previous studies had demonstrated that tree growth was impacted by smelter emissions and that forest floor lead concentrations could be used as a proxy for atmospheric pollutant depositions. Samples were analysed for Al, Pb (concentrations and isotope ratios), basic cations (Ca, K, P, and Mg) and Zr. Mass balance calculations were performed on soil profiles to assess vertical migration of elements. Pb concentrations in litter diminished gradually with distance from the smelter. The Pb isotope ratios in these organic soil layers were close to those measured in the Murdochville ores. These patterns were not encountered in mineral soil layers. Pb isotope ratios in these layers were close to those measured in uncontaminated geological materials, and Pb concentrations and basic cation depletions were not related to the proximity of the smelter. Growth reduction was closely associated with litter Pb concentrations, which were used as a proxy for atmospheric deposition, but was not correlated with any elemental concentration or cation depletion measured in mineral soil layers. Our overall results suggest that trees responded mainly to direct atmospheric emissions, which caused foliar damage, rather than to soil chemistry modifications.     

Modeling mobile source emissions during traffic jams in a micro urban environment

Urbanization typically involves a continuous increase in motor vehicle use, resulting in congestion known as traffic jams. Idling emissions due to traffic jams combine with the complex terrain created by buildings to concentrate atmospheric pollutants in localized areas. This research simulates emissions concentrations and distributions for a congested street in Minsk, Belarus. Ground-level (up to 50-meters above the street's surface) pollutant concentrations were calculated using STAR (version 3.10) with emission factors obtained from the U.S. Environmental Protection Agency, wind speed and direction, and building location and size. Relative emissions concentrations and distributions were simulated at 1-meter and 10-meters above street level. The findings demonstrate the importance of wind speed and direction, and building size and location on emissions concentrations and distributions, with the leeward sides of buildings retaining up to 99 percent of the emitted pollutants within 1-meter of street level, and up to 77 percent 10-meters above the street.     

Road traffic impact on urban water quality: a step towards integrated traffic,air and stormwater modelling

Methods for simulating air pollution due to road traffic and the associated effects on stormwater runoff quality in an urban environment are examined with particular emphasis on the integration of the various simulation models into a consistent modelling chain. To that end, the models for traffic, pollutant emissions, atmospheric dispersion and deposition, and stormwater contamination are reviewed. The present study focuses on the implementation of a modelling chain for an actual urban case study, which is the contamination of water runoff by cadmium (Cd), lead (Pb), and zinc (Zn) in the Grigny urban catchment near Paris, France. First, traffic emissions are calculated with traffic inputs using the COPERT4 methodology. Next, the atmospheric dispersion of pollutants is simulated with the Polyphemus line source model and pollutant deposition fluxes in different subcatchment areas are calculated. Finally, the SWMM water quantity and quality model is used to estimate the concentrations of pollutants in stormwater runoff. The simulation results are compared to mass flow rates and concentrations of Cd, Pb and Zn measured at the catchment outlet. The contribution of local traffic to stormwater contamination is estimated to be significant for Pb and, to a lesser extent, for Zn and Cd; however, Pb is most likely overestimated due to outdated emissions factors. The results demonstrate the importance of treating distributed traffic emissions from major roadways explicitly since the impact of these sources on concentrations in the catchment outlet is underestimated when those traffic emissions are spatially averaged over the catchment area.     

The sensitivity of modeled ozone to the temporal distribution of point, area, and mobile source emissions in the eastern United States

Ozone remains one of the most recalcitrant air pollution problems in the US. Hourly emissions fields used in air quality models (AQMs) generally show less temporal variability than corresponding measurements from continuous emissions monitors (CEM) and field campaigns would imply. If emissions control scenarios to reduce emissions at peak ozone forming hours are to be assessed with AQMs, the effect of emissions' daily variability on modeled ozone must be understood. We analyzed the effects of altering all anthropogenic emissions' temporal distributions by source group on 2002 summer-long simulations of ozone using the Community Multiscale Air Quality Model (CMAQ) v4.5 and the Carbon Bond IV (CBIV) chemical mechanism with 12 km resolution. We find that when mobile source emissions were made constant over the course of a day, 8-h maximum ozone predictions changed by ±7 parts per billion by volume (ppbv) in many urban areas on days when ozone concentrations greater than 80 ppbv were simulated in the base case. Increasing the temporal variation of point sources resulted in ozone changes of +6 and −6 ppbv, but only for small areas near sources. Changing the daily cycle of mobile source emissions produces substantial changes in simulated ozone, especially in urban areas at night; results suggest that shifting the emissions of NO_x from day to night, for example in electric powered vehicles recharged at night, could have beneficial impacts on air quality.     

A hybrid modeling approach to resolve pollutant concentrations in an urban area

A modeling tool that can resolve contributions from individual sources to the urban environment is critical for air-toxics exposure assessments. Air toxics are often chemically reactive and may have background concentrations originated from distant sources. Grid models are the best-suited tools to handle the regional features of these chemicals. However, these models are not designed to resolve pollutant concentrations on local scales. Moreover, for many species of interest, having reaction time scales that are longer than the travel time across an urban area, chemical reactions can be ignored in describing local dispersion from strong individual sources making Lagrangian and plume-dispersion models practical. In this study, we test the feasibility of developing an urban hybrid simulation system. In this combination, the Community Multi-scale Air Quality model (CMAQ) provides the regional background concentrations and urban-scale photochemistry, and local models such as Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) and AMS/EPA Regulatory Model (AERMOD) provide the more spatially resolved concentrations due to local emission sources. In the initial application, the HYSPLIT, AERMOD, and CMAQ models are used in combination to calculate high-resolution benzene concentrations in the Houston area. The study period is from 18 August to 4 September of 2000. The Mesoscale Model 5 (MM5) is used to create meteorological fields with a horizontal resolution of 1×1 km². In another variation to this approach, multiple HYSPLIT simulations are used to create a concentration ensemble to estimate the contribution to the concentration variability from point sources. HYSPLIT simulations are used to model two sources of concentration variability; one due to variability created by different particle trajectory pathways in the turbulent atmosphere and the other due to different flow regimes that might be introduced when using gridded data to represent meteorological data fields. The ensemble mean concentrations determined by HYSPLIT plus the concentrations estimated by AERMOD are added to the CMAQ calculated background to estimate the total mean benzene concentration. These estimated hourly mean concentrations are also compared with available field measurements.     

Concentration of atmospheric pollutants in the gaseous emissions of medical waste incinerators

The purpose of this paper is to quantify the production of medical waste from a general hospital and to evaluate the atmospheric pollutant concentrations in gaseous emissions associated with its incineration. A 3.8 kg (bed.day)-1 production of medical waste was estimated for 1998; its incineration is related with an ash production of 0.3-0.4 kg (bed.day)-1. The concentrations of atmospheric pollutants were estimated using emission factors, comparing the effluents with and without control of atmospheric pollutants. The calculated concentrations were compared with the emission limits established by Portuguese legislation. The results indicate that, if there is no control of atmospheric pollutants, their concentrations exceed the established limits. This is observed even if correct operation and maintenance procedures are used. The emission concentrations of dioxins are higher than the Portuguese emission limit, which is particularly worrying due to the high toxicity of some of these compounds. Generally, it is possible to reduce pollutant concentrations if appropriate control equipment is used. The conclusions obtained clearly justify the great concern regarding air pollution associated with medical waste incinerators currently operating in Portugal.     

Managing emissions from highly industrialized areas: Regulatory compliance under uncertainty

The use of regulatory and compliance-based modeling for air quality impact assessment is invariably relied upon to predict future air quality under various management scenarios particularly where air quality monitoring data are limited. This paper examines the dispersion from a multi-stack cement manufacturing complex with associated quarries and transport activities for regulatory compliance under uncertain emission and meteorological conditions. The concentrations of CO, NO_x, SO₂ and PM at sensitive receptor locations were used as indicators in comparison to World Health Organization (WHO) interim guidelines. Exceedance exposure areas were delineated under bounded uncertainties in input emission factors and meteorological parameters. Planning and management initiatives were tested to control/minimize potential exposure. Compared to the case of low emissions and actual meteorological conditions, the consideration of worst emissions coupled to worst meteorological conditions enlarged the boundaries of the exceedance exposure areas considerably. The implementation of best available technologies and enforcement of emission standards improved air quality in the region significantly and lowered the exposure at many population centers to below health standards. Uncertainty in the output of atmospheric dispersion models continues to play a significant role to be considered at the point where science is translated into political decision making.     

Air quality impacts of distributed energy resources implemented in the northeastern United States

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.     

Application of a scenario-based modeling system to evaluate the air quality impacts of future growth

The structure and design of future urban development can have significant adverse effects on air pollutant emissions as well as other environmental factors. When considering the future impact of growth on mobile source emissions, we generally model the increase in vehicle kilometers traveled (VKT) as a function of population growth. However, diverse and poorly planned urban development (i.e., urban sprawl) can force higher rates of motor vehicle use and in return increase levels of pollutant emissions than alternative land-use scenarios. The objective of this study is to develop and implement an air quality assessment tool that takes into account the influence of alternative growth and development scenarios on air quality.The use of scenario-based techniques in land use planning has been around since the late 1940s and been tested in many different applications to aid in decision-making. In this study, we introduce the development of an advanced interactive scenario-based land use and atmospheric chemistry modeling system coupled with a GIS (Geographical Information System) framework. The modeling system is designed to be modular and includes land use/land cover information, transportation, meteorological, emissions, and photochemical modeling components. The methods and modularity of the developed system allow its application to both broad areas and applications.To investigate the impact of possible land use change and urbanization, we evaluated a set of alternative future patterns of land use developed for a study area in Southwest California. Four land use and two population variants (increases of 500k and 1M) were considered. Overall, a Regional Low-Density Future was seen to have the highest pollutant emissions, largest increase in VKT, and the greatest impact on air quality. On the other hand, a Three-Centers Future appeared to be the most beneficial alternative future land-use scenario in terms of air quality. For all cases, the increase in population was the main factor leading to the change on predicted pollutant levels.     

Review of Singapore's air quality and greenhouse gas emissions: current situation and opportunities

Singapore has many environmental accomplishments to its credit. Accessible data on air quality indicates that all criteria pollutants satisfy both U.S. Environmental Protection Agency (EPA) and World Health Organization (WHO) air quality standards and guidelines, respectively. The exception is PM2.5 (particles with an aerodynamic diameter < or = 2.5 microm), which is not currently considered a criteria pollutant in Singapore but may potentially be the major local air pollution problem and cause for health concern. Levels of other airborne pollutants as well as their physical and chemical processes associated with local formation, transformation, dispersion, and deposition are not known. According to available emission inventories, Singapore contribution to the total atmospheric pollution and carbon budget at the regional and global scales is small. Emissions per unit gross domestic product (GDP) are low compared with other countries, although Singapore's per-capita GDP and per-capita emissions are among the highest in the world. Some information is available on health effects, but the impacts on the ecosystem and the complex interactions of air pollution and climate change at a regional level are also unknown. This article reviews existing available information on atmospheric pollution and greenhouse gas emissions and proposes a multipollutant approach to greenhouse gas mitigation and local air quality. Singapore, by reducing its per-capita emissions, increasing the availability of information (e.g., through regularly publishing hourly and/or daily PM2.5 concentrations) and developing a research agenda in this area, would likely be seen to be a model of a high-density, livable, and sustainable city in Southeast Asia and other tropical regions worldwide.     

Concentration of Atmospheric Pollutants in the Gaseous Emissions of Medical Waste Incinerators

ABSTRACT

The purpose of this paper is to quantify the production of medical waste from a general hospital and to evaluate the atmospheric pollutant concentrations in gaseous emissions associated with its incineration. A 3.8 kg (bed.day)^-1 production of medical waste was estimated for 1998; its incineration is related with an ash production of 0.3-0.4 kg (bed.day)^-1. The concentrations of atmospheric pollutants were estimated using emission factors, comparing the effluents with and without control of atmospheric pollutants. The calculated concentrations were compared with the emission limits established by Portuguese legislation. The results indicate that, if there is no control of atmospheric pollutants, their concentrations exceed the established limits. This is observed even if correct operation and maintenance procedures are used. The emission concentrations of dioxins are higher than the Portuguese emission limit, which is particularly worrying due to the high toxicity of some of these compounds. Generally, it is possible to reduce pollutant concentrations if appropriate control equipment is used. The conclusions obtained clearly justify the great concern regarding air pollution associated with medical waste incinerators currently operating in Portugal.     

Gaseous Sulfur Pollutants from Urban and Natural Sources

Major aspects of the circulation through the atmospheric environment of sulfur pollutants have been estimated, including source magnitudes, residual atmospheric concentrations, and scavenging processes. The compounds considered include SO₂ and H₂S, as well as sulfates. One-third of the sulfur reaching the atmosphere comes from pollutant sources, mainly as SO₂. Within the atmosphere there is a net transfer of sulfur from land to ocean areas. Pollutant sources annually amount to 73 × 10⁶ tons as sulfur while natural sources amount to 142 × 10⁶ tons, mainly as H₂S and sulfate sea spray. More than two thirds of the natural and pollutant sulfur emissions occur in the northern hemisphere. When only pollutant emissions are considered, 93 per cent occur in the northern hemisphere.     

The sensitivity of the CHIMERE model to emissions reduction scenarios on air quality in Northern Italy

The sensitivity of the CHIMERE model to emission reduction scenarios on particulate matter PM2.5 and ozone (O₃) in Northern Italy is studied. The emissions of NO_x, PM2.5 SO₂, VOC or NH₃ were reduced by 50% for different source sectors for the Lombardy region, together with 5 additional scenarios to estimate the effect of local measures on improving the air quality for the Po valley area. Firstly, we evaluate the model performance by comparing calculated surface aerosol concentrations for the standard case (no emission reductions) with observations for January and June 2005. Calculated monthly mean PM10 concentrations are in general underestimated. For June, modelled PM10 concentrations slightly overestimate the measurements. Calculated monthly mean SO₄, NO₃^?, NH₄⁺ concentrations are in good agreement with the observations for January and June. Secondly, the model sensitivity of emission reduction scenarios on PM2.5 and O₃ calculated concentrations for the Po valley area is evaluated. The most effective scenarios to abate PM2.5 concentration are based on the SNAP2 (non-industrial combustion plants) and SNAP7 (road traffic) sectors, for which the NO_x and PM2.5 emissions are reduced by 50%. The number of days that the 2015 PM2.5 limit value of 25 μg m^?3 in Milan is exceeded by reducing primary PM2.5 and NO_x emissions for SNAP2 and 7 by 50%, does not change in January when compared to the standard case for the Milan area. It appears that 40% of the PM2.5 concentration in the greater Milan area is caused by the emissions surrounding the Lombardy region and from the model boundary conditions.This study also showed that a more effective pollutant reduction (emissions) per ton of pollutant reduced (concentrations) for the greater Milan area is obtained by reducing the primary PM2.5 emissions for SNAP7 by 50%. The most effective scenario on PM2.5 decrease for which precursor emissions are reduced is achieved by reducing SO₂ emissions by 50% for SNAP7.Our study showed that during summer time, the largest reductions in O₃ concentrations are achieved for SNAP7 emission reductions, when volatile organic compounds (VOCs) are reduced by 50%.     

Air Quality Impacts of Distributed Energy Resources Implemented in the Northeastern United States

Abstract

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 (PM_2.5) concentrations reach 3 μg/m3 and are located off the coast of New Jersey and New York. The main contribution to decreased PM_2.5 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.     

Hydrocarbon emissions from industrial release events in the Houston-Galveston area and their impact on ozone formation

Ambient measurements have shown that ozone formation in the Houston-Galveston area of Texas is frequently much more rapid than in other urban areas. One of the contributing factors is believed to be short-term episodic or “event” emissions from industrial facilities, particularly releases that contain significant mass fractions of highly reactive volatile organic compounds (HRVOCs). In this work, time series analyses are used to compare average annual flow rates for air pollutant emissions with those released during reported emission events. The results indicate that the magnitude and frequency of HRVOC event emissions are an important element in accurately reflecting ozone precursor emission patterns in the Houston-Galveston area, particularly in Harris, Brazoria, Galveston, and Chambers counties. More than 50% of the reported episodic (event) emissions of HRVOCs are ethene and approximately a third are propene; the remainders are isomers of butene and 1,3-butadiene. Most events last less than 24 h. The mass released in an event can vary from a few hundred to more than 100,000 lb, and the dominant type of industrial source is chemical manufacturers (SIC 2869). Daily emissions from a single facility can vary from annual average emissions by multiple orders of magnitude at a frequency of several times a year. Because there are so many facilities in the Houston-Galveston area, HRVOC emission variability of this magnitude can be expected daily, at some time and some location in the Houston-Galveston area. If the emission variability occurs at times and locations where atmospheric conditions are conducive to ozone formation, both ambient data and photochemical modeling indicate that industrial emission events can lead to elevated concentrations of ozone. Specifically, peak, area-wide ozone concentration can be increased by as much as 100 ppb for large HRVOC emission events.     

Spatial inhomogeneity in pollutant concentrations, and their implications for air quality model evaluation

The Southern California Air Quality Study database provides a valuable resource with which to test urban-scale photochemical models and to achieve a better understanding of the atmospheric dynamics of pollutant formation. The CIT model was evaluated using the SCAQS database according to traditional model performance guidelines. A first application, reported previously, focused on model enhancement and application of the model to the 27–29 August 1987 episode. This study evaluates the CIT model using the 24–25 June SCAQS episode, providing further evaluation of the model. Results show that the CIT airshed model can follow the diurnal variations of reactive species and the transport for relatively unreactive species. The normalized gross error for ozone was 31 % in June compared to 38% in August. However, to fully judge model performance in proper perspective, a question arises: “How well do the measurements reflect the air quality surrounding the monitoring station, not just in that location?” This is an important but seldom quantitatively considered factor, not only in model evaluation but in the study of health effects as well. Analyses indicate that individual concentration measurements only approximately represent the true volume-averaged concentrations within a computational grid cell and that significant spatial variations exist. Thus any evaluation of models using these data sets should take these local variations into consideration. A series of tests found that the local inhomogeneities had a normalized gross error in the range of 25–45% depending on the pollutant. In this context, the performance of the CIT model is consistent with known modeling limitations such as emissions inventories and sub-grid scale variation of observations.     

A methodology to urban air quality assessment during large time periods of winter using computational fluid dynamic models

The representativeness of point measurements in urban areas is limited due to the strong heterogeneity of the atmospheric flows in cities. To get information on air quality in the gaps between measurement points, and have a 3D field of pollutant concentration, Computational Fluid Dynamic (CFD) models can be used. However, unsteady simulations during time periods of the order of months, often required for regulatory purposes, are not possible for computational reasons. The main objective of this study is to develop a methodology to evaluate the air quality in a real urban area during large time periods by means of steady CFD simulations. One steady simulation for each inlet wind direction was performed and factors like the number of cars inside each street, the length of streets and the wind speed and direction were taken into account to compute the pollutant concentration. This approach is only valid in winter time when the pollutant concentrations are less affected by atmospheric chemistry. A model based on the steady-state Reynolds-Averaged Navier–Stokes equations (RANS) and standard k-? turbulence model was used to simulate a set of 16 different inlet wind directions over a real urban area (downtown Pamplona, Spain). The temporal series of NO_x and PM₁₀ and the spatial differences in pollutant concentration of NO₂ and BTEX obtained were in agreement with experimental data. Inside urban canopy, an important influence of urban boundary layer dynamics on the pollutant concentration patterns was observed. Large concentration differences between different zones of the same square were found. This showed that concentration levels measured by an automatic monitoring station depend on its location in the street or square, and a modelling methodology like this is useful to complement the experimental information. On the other hand, this methodology can also be applied to evaluate abatement strategies by redistributing traffic emissions.     

Transferring the heterogeneity of surface emissions to variability in pollutant concentrations over urban areas through a chemistry-transport model

Horizontal resolution of grid-based chemistry-transport models is limited to a few square kilometers which has been proved insufficient for assessing human exposure and health impact. We propose a general methodology, applicable on any kind of grid-based air-quality model, that combines subgrid scale information on emission and land-use data in order to disaggregate the grid-averaged emission flux into a set of source-specific components (subgrid-environments). Different subgrid concentrations are calculated inside each one of these environments providing a direct estimate of pollutant variability along with the ‘standard’ grid-averaged model output. The method was first validated over a controlled emissions case by comparing concentrations modeled in the subgrid-environments with concentrations modeled directly at higher model resolution and next over a real case-study, where subgrid concentrations were compared with monitor data from sites representing different types of urban environments (i.e. roads and residential blocks). It was shown that the method is capable to yield accurate estimates of small scale pollutant variability.     

Increase in summer European ozone amounts due to climate change

The local and regional distribution of pollutants is significantly influenced by weather patterns and variability along with the spatial patterns of emissions. Therefore, climatic changes which affect local meteorological conditions can alter air quality. We use the regional air quality model CHIMERE driven by meteorological fields from regional climate change simulations to investigate changes in summer ozone mixing ratios over Europe under increased greenhouse gas (GHG) forcing. Using three 30-year simulation periods, we find that daily peak ozone amounts as well as average ozone concentrations substantially increase during summer in future climate conditions. This is mostly due to higher temperatures and reduced cloudiness and precipitation over Europe and it leads to a higher number of ozone events exceeding information and warning thresholds. Our results show a pronounced regional variability, with the largest effects of climate change on ozone concentrations occurring over England, Belgium, Germany and France. The temperature-driven increase in biogenic emissions appears to enhance the ozone production and isoprene was identified as the most important chemical factor in the ozone sensitivity. We also find that summer ozone levels in future climate projections are similar to those found during the exceptionally warm and dry European summer of 2003. Our simulations suggest that in future climate conditions summer ozone might pose a much more serious threat to human health, agriculture and natural ecosystems in Europe, so that the effects of climate trends on pollutant amounts should be considered in future emission control measures.     

Predicted changes in summertime organic aerosol concentrations due to increased temperatures

Changes in summertime organic aerosol (OA) concentrations in the Eastern U.S. are investigated for different temperature change scenarios using the chemical transport model PMCAMx-2008. OA is simulated using the volatility basis set approach, assuming that the primary emissions are semi-volatile and that the intermediate volatile and semi-volatile organic compounds are oxidized in the gas phase, resulting in products with lower volatility. For the basic temperature change scenario where biogenic emissions are kept constant, ground-level OA decreases by −0.3% K⁻¹ on average. Increases in the north (+0.1% K⁻¹) and decreases in the south (−0.5% K⁻¹) are predicted. The effect of the uncertain temperature dependence of the aging rate constant is modest, changing the OA by only 0.1% K⁻¹ over the temperature-independent case. For the more realistic scenario in which biogenic OA precursor emissions are allowed to increase with temperature (up to 10% K⁻¹), however, average OA increases by 4.1% K⁻¹, with even higher increases in southern regions. These results suggest that as temperature increases, complicated changes in production, partitioning and chemical aging will take place. Nevertheless, the change in biogenic emissions and subsequent production of biogenic OA is more than an order of magnitude more important than the changes in the rates of chemical and physical atmospheric processes.