A Modeling Study of the Impact of a Power Plant on Ground-Level Ozone in Relation to its Location: Southwestern Spain as a Case Study

The impact of atmospheric industrial emissions on secondary pollutant formation depends on many factors; one of the most important being the environmental setting in which the industry is located. The environmental setting affects an industry’s impact on ozone levels through both the air mass dispersion (a function of topography and wind patterns) and the emissions of organic volatile compounds (VOC) and nitrogen oxides (NO _x ) in the area. This model-based study shows how the sensitivity of surface ozone changes with the choice of source location. For the analysis, seven points distributed along the Tinto–Guadalquivir Basin (in the Southwestern Iberian Peninsula) were selected. This area is characterized by the close proximity of natural environments and crop fields to cities, roads, and industrial areas with high NO _x emissions. Natural VOC emissions represent more than 60% of the total non-methane volatile organic compounds emitted in the study area. The results reveal that the largest increases in ozone levels are produced when the industry is located both far away from NO _x emission sources and near to biogenic VOC emissions. Furthermore, the highest increases over the hourly and 8-hourly maximums, as well as the highest accumulated daily values, are found in areas characterized by high VOC/NO _x emission ratios and NO _x sensitivity. The study of the recurrent meteorological patterns along with the distribution of chemical indicators of the O₃–NO _x –VOC sensitivity allows the determination of the industry’s geographical impact on ozone levels. This information enables air quality managers to decide the future location of an industry minimizing its impact on smog levels.     

Towards a Science-Based Integrated Ozone-Fine Particle Control Strategy

Epidemiology studies relating health effects to ambient levels of ozone and fine particles have led to the modification of standards in the United States for these pollutants (substitution of an 8-h standard for ozone at 80 ppbv, and addition of 24-h and annual standards for fine particles). The interrelationships of these pollutants in the atmosphere suggest the need for an integrated, science-based strategy for their control. Secondary ozone formation has been controlled through emission controls on VOC and NO_x precursors. Fine particles are secondary products largely resulting from the oxidation of precursors (SO₂, NO_x, and VOCs). The key intermediates in both types of secondary process are free radical species and the photochemically labile compounds that produce them in the atmosphere. However, due to the complex and nonlinear nature of the processes, reductions in precursors may lead to unexpected changes in ozone and fine particle formation rates. For example, reduction in NO_x emissions may reduce ozone and nitric acid levels, but lead also to increased rates of sulfate formation in clouds and increased ammonia availability for neutralization of acidic sulfate aerosols. Reductions of SO₂ may reduce aerosol sulfate levels in the summer, but have no effect in other seasons. Reductions in VOCs may reduce ozone levels in urban core areas, but not elsewhere. An integrated, regionally and seasonally specific, emission reduction strategy is needed to cost-effectively reduce both ozone and fine particle levels.     

The relative effectiveness of NOx and VOC strategies in reducing Northeast U.S. ozone concentrations

This investigation was conducted to compare the relative benefits of controlling emissions of VOC vs. NO_x for reducing tropospheric O₃ (smog) concentrations in the Northeast United States. Because of the nonlinear nature of O₃ photochemistry, controls on NO_x emissions could actually result in increases in O₃ depending on the relative amount of VOC present and meteorological conditions. The Regional Oxidant Model (ROM) was used as the tool for estimating the impacts of different VOC and NO₃ strategies. Scenarios simulated include a future baseline and separate strategies with controls on just NO, just VOC, and a combination of VOC and NO_x controls. The results indicate that in general, NO_x controls are more beneficial across the region than VOC controls. However, for several large urban areas, NO_x controls were predicted to result in higher O₃ than VOC controls. Also, the relative benefits of VOC and NO_x controls varied from day-to-day suggesting a dependency on meteorological conditions. Given the variable nature of the effects of NO_x controls, additional modeling using more spatially resolved models is warranted to identify specific strategies for attainment of the ozone NAAQS in individual areas.     

A regional scale model for the calculation of episodic concentrations and depositions of acidifying components

An eulerian long-range transport model for the calculation of concentrations of SO₂, SO₄, NO _x , and NO₃ and wet and dry depositions of SO _x (sum of SO₂ and SO₄) and NO _y (sum of NO, NO₂ and NO₃) over Europe is presented. The model is developed in such a way that only routinely available, analyzed or prognostic meteorological fields are required as input data. In this way it is possible to obtain a forecast of the air quality during smog episodes. For evaluation of smog episodes the model provides a way to estimate the contributions of different sources and the effect of emission scenarios. The model has been evaluated for four winter and three summer episodes. The modeled concentrations of SO₂ and SO, are in agreement with the available measurements. A less good agreement is found for NO₂ and NO _x (sum of NO and NO₂) concentrations. For these components the model tends to underpredict the measured values.     

Efficacy of nitrogen oxides and hydrocarbons emissions controls in ozone attainment strategies as predicted by the Urban Airshed Model

The primary object of this paper is to provide a preliminary assessment of the effectiveness of NO _x vs Volatile Organic Compounds (VOC) emissions control options in improving O₃ air quality over the New York metropolitan area. To this end, we have applied the Urban Airshed Model (UAM) with the Carbon Bond IV (CB-IV) chemical mechanism utilizing the results of the Regional Oxidant Model (ROM) for the specification of initial/boundary concentrations and wind fields to the UAM. After examining the sensitivity of the predicted O₃ concentrations to initial/boundary conditions and biogenic emissions, we have evaluated the impact of various hypothetical emissions reduction options on O₃ air quality. Nested ROM/UAM simulations with an across-the-board reduction of 75% in the NO _x and VOC emissions from sources located within the New York metropolitan area indicate that the option of VOC-only control is superior to the NO _x -only control in reducing not only peak O₃ levels over the entire modeling domain but also population exposure to unhealthy O₃ levels. The model predicts that the combined 75% NO _x and VOC control option also reduces the peak O₃ concentration, but the improvement in O₃ air quality is less than that predicted for the 75% VOC-only control strategy. Additional modeling analyses with different mix and levels of emissions control and meteorological conditions are needed to confirm these preliminary findings.     

The role of nitrogen oxides in oxidant production as predicted by the Regional Acid Deposition Model (RADM)

Regional oxidant distributions produced under various atmospheric conditions and emission scenarios are investigated using the Regional Acid Deposition Model (RADM). RADM is a complex, evolving three-dimensional Eulerian model that describes the chemistry, transport and deposition of tropospheric trace species including SO₂, sulfate, NO _x and volatile organic compounds as well as O₃, other major oxidants and acids. The model calculates the short-term temporal evolution of atmospheric trace gas concentrations and their deposition on the regional scale. This study is focused on oxidant production in the eastern United States and southeastern Canada. The influence of atmospheric conditions is explored by comparing three characteristic winter, summer and spring/fall cases. Base-case 1985 emissions of SO _x , NO _x , volatile organic compounds (VOCs), NH₃ and CO are specified using the comprehensive pollutant emissions inventory developed as part of the National Acid Precipitation Assessment Program (NAPAP). The perturbed case, which represents projected anthropogenic emission changes for 2010, indicates changes in daily total 80 km grid average NO _x emissions ranging from increases of 75% to decreases of 45% and VOC emission changes ranging from increases of 65% to decreases of 20%. The largest NO _x emission changes occur in the northeast, and the largest VOC changes occur in the Gulf Coast area. Ground level grid average midday O₃ concentrations for the 1985 emission cases are highest (on the order of 70 to 100 ppb) in the New York City and Houston metropolitan areas for the summer and spring cases; the summer case also indicates relatively high grid average O₃ concentrations of greater than 80 ppb in the southeast. Winter case values are much lower than summer O₃ values throughout the region, with highs of 40 to 50 ppb occurring in the southeast and the Great Lakes area. Changes in NO _x and other emissions under the complex 2010 emissions scenario for the summer case result in maximum O₃ concentration reductions of 10% in the Houston area and increases in O₃ of a few percent in some rural areas of the southeast. This study underscores the need for more comprehensive assessment of the complex relationships among regional emission changes, oxidant production and atmospheric conditions.     

Tropospheric Ozone in Alpine Forest Sites: Air Quality Monitoring and Statistical Data Analysis

Plants represent one of the major sinks for tropospheric ozone that, at high concentrations, can affect plants' physiological activity with consequent serious damage. A research project has been promoted by the Lombardy Foundation for the Environment to investigate the effects of air pollution on forest ecosystems. The areas of study are located on the southern slopes of the Italian Alps in two valleys, only 10 km apart, selected because of their different plant injury: Val Gerola and Val Masino. Air quality (O₃, NO_x, SO_x, VOC) and meteorological parameters were monitored during four summer seasons (1994-97) using automatic sampling devices providing hourly mean values for each variable. Data analysis showed very different ambient ozone concentrations at the two sites, with average concentration values observed in the more damaged valley (Val Gerola) twice those measured at the other site. Multivariate data analyses have been used to interpret the observed differences in long-term O₃ exposure between the two sites and to identify possible underlying processes.     

Modeling study of SO x and NO x transport during the January 1985 SMOG episode

For the January 1985 smog episode concentrations of SO₂, sulphate (SO₄), NO _x (sum of NO and NO₂) and nitrate (NO₃) have been calculated for north-western Europe by means of an atmospheric transport model. The unfavorable dispersion conditions (moderate to low wind speeds, a low mixing height and a strong inversion) and a reduced dry deposition over the snow-covered or frozen soil, in combination with increased space heating emissions due to the exceptionally cold weather, gave rise to high ground level concentrations. In order to study the effectiveness of control measures during this type of episodes, calculations were made for various emission scenarios. The results were evaluated for four receptor areas, two areas relatively close to the major sources (The Netherlands and the Black Forest) and two more remote areas (Scotland and the SW coast of Sweden, near Gothenburg).     

The Importance of Nitrogen Oxides for the Exceedance of Critical Thresholds in the Nordic Countries

Impacts of air pollutants and especially acidification in ecosystems have been of serious concern in the Nordic countries since the 1970s. The current approach to assess several pollutants (sulfur and nitrogen oxides, ammonia, volatile organic compounds) and their effects (acidification, eutrophication and ground-level ozone) simultaneously is extremely complex. This study explored the relative role of nitrogen oxides in environmental impacts in the Nordic countries. The share of NO_x in the exceedances of critical loads, the long-term ecosystem protection targets, was found to be roughly 25% in acidification and 50% in eutrophication. The contribution of NO_x emissions to ground-level ozone formation was considered important, as NO_x is the limiting precursor in ozone formation in the Nordic countries. The comparison of observed and modeled accumulated ozone concentrations (AOT40) for the early 1990s shows noticeable differences in the Nordic area, partly due to the sensitivity of the AOT40 indicator to the 40 ppb threshold value.     

Chemical Composition of Air, Soil and Vegetation in Forests of the Silesian Beskid Moutains, Poland

For the first time concentrations of trace nitrogenous (N) air pollutants, gaseous nitric acid (HNO₃), nitrous acid (HNO₂), ammonia (NH₃), and fine particulate nitrate (NO₃) and ammonium (NH₄), were measured in the montane forests of southern Poland. Determinations were performed in two forest locations of the Silesian Beskid Mountains in the western range of the Carpathian Mountains, and in an industrial/urban location in Karowice, Poland. The measurements performed in summer 1997 with honeycomb denuder/filter pack systems showed elevated concentrations of the studied pollutants. These findings agree with the low carbon/nitrogen (C/N) ratios and the results of ¹⁵N analyses of soil and moss samples. High concentrations of N air pollutants help to explain previously determined high levels of NO₃ and NH4 deposition to Norway spruce (Picea abies Karst.) canopies in these mountains. Ambient concentrations of sulfur dioxide (SO2) and ozone (O3) were elevated and potentially phytotoxic. Deficiencies of phosphorus (P) and magnesium (Mg) in Norway spruce foliage were found while concentrations of other nutrients were normal.     

Ozone Formation Potentials of Volatile Organic Compounds and Ozone Sensitivity to Their Emission in the Megacity of São Paulo, Brazil

In the present study, a three-dimensional Eulerian photochemical model was employed to estimate the impact that organic compounds have on tropospheric ozone formation in the Metropolitan Area of São Paulo (MASP). In the year 2000, base case simulations were conducted in two periods: August 22–24 and March 13–15. Based on the pollutant concentrations calculated by the model, the correlation coefficient relative to observations for ozone ranged from 0.91 to 0.93 in both periods. In the simulations employed to evaluate the ozone potential of individual VOCs, as well as the sensitivity of ozone to the VOC/NO _x emission ratio, the variation in anthropogenic emissions was estimated at 15% (according to tests performed previously variations of 15% were stable). Although there were significant differences between the two periods, ozone concentrations were found to be much more sensitive to VOCs than to NO _x in both periods and throughout the study domain. In addition, considering their individual rates of emission from vehicles, the species/classes that were most important for ozone formation were as follows: aromatics with a kOH?>?2?×?10⁴ ppm^?1 min^?1; olefins with a kOH?<?7?×?10⁴ ppm^?1 min^?1; olefins with a kOH?>?7?×?10⁴ ppm^?1 min^?1; ethene; and formaldehyde, which are the principal species related to the production, transport, storage and combustion of fossil fuels.     

Investigating the Real Air Pollution Exchange at Urban Sites Based on Time Variation of Columnar Content of the Components

As a new approach, urban air pollution was characterised by the variation of columnar content of the pollutants. Columnar content (CC) was estimated as the product of the pollutant??s mixing ratio and the mixing height. Mixing ratio data of the Metropolitan Air Quality Monitoring Network of Budapest were used, whilst mixing height was calculated by the meteorological AERMET model code. Time variation of CC refers to the real pollution exchange in the atmosphere that allows direct investigation of the emissions as well as post-emission modifications of the pollutants (such as chemical degradation or production). The diurnal urban CO cycle was found to be determined by two or three main influx peaks according to the traffic pattern of the site. The diurnal variation of NO _x level was found to be driven by traffic emission as well. Variant ratios of NO _x to CO influxes obtained for the different locations of the city range from 0.12 to 0.23, probably according to the vehicle composition of the traffic. The daily balance of photochemical production, chemical degradation and deposition of ozone yielded negative or positive depending on the location. Negative balances imply that the polluted urban atmosphere is a net ozone neutraliser source. Entrainment from the free troposphere yielded the major contributor to the diurnal ozone level at each site. The diurnal urban PM₁₀ cycle was found to be determined by traffic emission during the morning and evening rush hours whilst secondary aerosol formation around noon. In the evening, high PM₁₀ level rise was observed due to direct traffic emission as well as rapid conversion of the fine aerosol fraction to the coarse fraction.     

Nitrogen oxides,regional transport,and ozone air quality: Results of a regional-scale model for the midwestern United States

An overview of the role of NO _x in the formation of rural O₃, regional transport and its potential impact on urban air quality is presented. An analysis of a specific O₃ excursion in southeast Michigan (8-2-90) is performed based on a combined urban and regional-scale model. The regional component of the model represents transport and photochemistry from sources as far away as Texas. Results suggest that rural O₃ and regional transport sensitive to NO _x emissions and relatively insensitive to changes in volatile organic carbon (VOC) emissions. This differs from the situation in urban areas, where O₃ is sensitive to both NO _x and VOC. Regional transport and upwind NO _x emissions have a significant impact on peak O₃ in Detroit. Implications for urban and regional-scale abatement strategies are discussed.     

Evaluation of extreme pollution episodes over Lithuania in 1980–1994

The investigation of SO₂, NO₂, benzo(a)pyrene (BP) and soot (C_el) has been carried out daily in the atmospheric air in the background station Preila (East shore of the Baltic Sea) since 1980. Over this period, daily concentrations of pollutants varied in the wide intervals in warm and cold period as well. From 15 years data typical episodes of highest and lowest concentrations of pollutants are chosen and analysed with respect to the air masses trajectories and meteorological conditions. The highest concentrations of SO₂, NO₂, BP, Cd were fixed, when the air masses passing Lithuania have been formed over Great Britain and Central Europe.     

Regulatory options under the U.S. Clean Air Act: The federal view

This paper documents the evolution of Environmental Protection Agency (EPA) policy concerning the relative roles that volatile organic compounds (VOCs) and oxides of nitrogen (NO_x) emissions play in ozone nonattainment planning for State implementation plans (SIPs). It further discusses possible new control requirements, including NO_x measures, that may be required as a result of pending Clean Air Act Amendments. In the early 1970's EPA guidance emphasized the use of VOC control measures to attain the ozone (formerly oxidant) ambient air quality standard. Little if any, control requirements applied to NO_x emissions. EPA continued to focus guidance requirements upon the control of VOCs during the planning efforts associated with the 1977 Clean Air Act amendments... 1979 SIPs, 1982 plans for long-term problem areas (extension areas), and other revisions to SIPs. Preliminary air quality modeling work to support these later planning efforts revealed that, in certain cases, there were potential benefits of NO_x control in addition to VOC. With this new insight, EPA's post-1987 policy proposal required states to look at the potential benefits of NO_x controls in areas with a nonmethane organic compound to NO_x ratio of 10∶1 or greater. In Clean Air Act Amendments currently being debated in the House and Senate, there is an uncertainty with regard to the role of NO_x controls. Possibilities under consideration range from the application of reasonably available control technology for 100 ton sources of NO_x to a clean fuel motor vehicle program within 42 months of enactment.     

Quantifying Local Creation and Regional Transport Using a Hierarchical Space–Time Model of Ozone as a Function of Observed NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>, a Latent Space–Time VOC Process,Emissions, and Meteorology

We explore the ability of a process-based space–time model to decompose 8-hour ozone on a given day and site into parts attributable to local emissions and regional transport, to provide space–time predictions, and to assess the efficacy of past and future emission controls. We model ozone as created plus transported plus an error with seasonally varying spatial covariance parameters. Created ozone is a function of the observed NO _x concentration, the latent VOC concentration, and solar radiation surrogates. Transported ozone is a weighted average of the ozone observed at all sites on the previous day, where the weights are a function of wind speed and direction. The latent VOC process mean includes emissions, temperature, and a workday indicator, and the error has seasonally varying spatial covariance parameters. Using likelihood methods, we fit the model and obtain one set of predictions appropriate for prediction backward in time, and another appropriate for predicting under hypothetical emission scenarios. The first set of predictions has a lower root-mean-squared error (RMSE) when compared to point observations than do the 36 km gridcell averages from the Community Mesoscale Air Quality Model (CMAQ) used by the EPA; the second set has the same RMSE as CMAQ, but under-predicts high ozone values.     

Projections of SO2, NOx,NH3 and VOC Emissions in East Asia Up to 2030

Starting from an inventory of SO₂, NO_x, VOC and NH₃ emissions for the years 1990 and 1995 in East Asia (Japan, South and North Korea, China, Mongolia and Taiwan), the temporal development of the emissions of the four air pollutants is projected to the year 2030 based on scenarios of economic development. The projections are prepared at a regional level (prefectures or provinces of individual countries) and distinguish more than 100 source categories for each region. The emission estimates are presented with a spatial resolution of 1×1 degree longitude/latitude. First results suggest that, due to the emission control legislation taken in the region, SO₂ emissions would only grow by about 46 percent until 2030. Emissions of NO_x and VOC may increase by 95 and 65 percent, respectively, mainly driven by the expected increase in road traffic volume. Ammonia, mainly emitted from agriculture, is projected to double by 2030.     

Bench Scale Evaluation of a Chemo-biochemical Process for Desulphurization of Gaseous Streams Containing Hydrogen Sulphide

Gases and suspended particulate matter are sampled and measured in situ at different sites within the city of Madrid to determinethe air pollution in the city. Lead concentrations in air are also determined. The information needed to assess levels of contaminants is obtained combining several analytical techniques,which provide real time concentration data of particles andgases. Particulate matter (PM), SO₂, CO, O₃, NO_x,NO₂, CH₄, total hydrocarbons and Pb were measured. Concentrations of pollutants are averaged over periods of hours,days, months and years. Variations of contaminant concentrationsin the last years are presented. Spatial and temporal distribution follows that of the traffic, the main source of pollution in Madrid City. Some specific measurements were carriedout to understand the influence of traffic emissions at themeasured site. Further, all measured concentrations never exceeded the European Union Directives.     

Approaching Cumulative Effects through Air Pollution Modelling

The research presented here represents a segment of a cumulative impact assessment of resource development in northeastern British Columbia. It considers point and area source emissions of sulphur and nitrogen oxides (SO₂ and NO _x , respectively), over a 2,156-km² area. With the exception of open burning, all emissions are from Upstream Oil and Gas (UOG) sector sources (SO₂, n?=?103; NO _x , n?=?250; area, n?=?25). AERMOD View? was used to estimate the maximum potential concentration and deposition of these pollutants over 1-h, 3-h, 24-h, and annual averaging periods. Results are compared with various thresholds and limits from the policy and scientific literature to assess the potential cumulative effects of these pollutants. Of the thresholds employed, exceedances of the 1-h and 24-h NO _x concentrations and the annual SO₂ concentration are predicted. There were no predicted exceedances of annual deposition thresholds (i.e., ??Critical Loads??). Maximum predicted concentrations vary between compounds and are related to boundary layer stability, elevation, and distance from sources. Comparison with nearby monitoring data indicated that predicted concentrations were reasonable and that AERMOD provides a useful tool for approaching the potential cumulative impacts of air pollution from multiple sources. While the accuracy of Gaussian-based annual deposition estimates is questioned, model enhancements that could extend the application to more comprehensive assessments are suggested. Lastly, the implications of predicted threshold violations for forest ecosystems and local forest-dependent First Nations communities are discussed.     

Advection fog formation associated with atmospheric aerosols due to combustion-related pollutants

A large amount of pollutants in highly industrialized areas is produced by a photochemical reaction of NO _x and SO _x , which is a result of the production of energy-related fuel combustion. These pollutants provide the major source of condensation nuclei for the formation of fog in the areas of busy highways, airports, seaports, etc. The present study simulates how these pollutants affect the formation of advection fog. Both microphysical and macrophysical processes are considered in investigating the time dependent evolution of the spectra of condensation nuclei associated with both polluted and clean atmospheres during the time period of advection fog formation. In the first part of the series of this paper, the initial aerosol population concerns a monodisperse, multi-component aerosol model. The results show that both SO _x , and NO _x as condensation nuclei provide great contributions in the formation of advection fog.