Measurement needs for developing and assessing ozone-control strategies

The monitoring programs needed to design control strategies differ from those required to assess the impact of the strategies on air quality. The former are short-term and intensive. They are designed to obtain the data required to apply an urban-scale grid model, like the Urban Airshed Model, or a combination of an urban-scale and regional-scale model, like the Regional Oxidant Model, to an area without having to assume important input data. Such measurements include three-dimensional pollutant and meteorological measurements throughout the modeling domain. Detailed and accurate emissions inventories are also required. Model validation should compare not only the O₃ predictions with actual data, but also include comparisons for NO _x , individual volatile organic compounds (VOC), and if possible, additional species such as PAN, H₂O₂, formaldehyde, and HNO₃. To assess the impact of control strategies, long-term monitoring networks that measure O₃, NO _x and speciated VOC are needed. O₃ trends should be examined using robust, meteorologically-adjusted O₃ statistics. Such statistics need to be related to a robust National Ambient Air Quality Standard.     

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.     

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 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 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.     

Analysis of major photochemical pollutants with meteorological factors for high ozone days in Istanbul, Turkey

Hourly ozone, NO _x and VOC concentrations, measured during 2001–2003 summer periods, are analyzed in order to examine the interaction patterns between the major photochemical pollutants in ?stanbul. 34 high ozone days throughout the summer periods of the three years are determined and examined in the study together with the meteorological parameters like temperature, wind and vertical structure of the atmosphere. The results show that high levels of ozone are observed mostly under anticyclonic conditions with relatively low wind speeds. High ozone days generally experienced maximum concentrations at afternoon hours and minimum concentrations are reached at rush hours due to NO _x – titration by traffic emissions. High negative correlations with NO _x up to -0.84 are observed at the Saraçhane station while higher correlations for VOC species, up to ?0.75, are calculated for Kadiköy station. Some individual episodes experiencing high ozone concentrations up to 310 μg m^?3 in the early morning hours are also studied. It is found that decreasing inversion heights in the early hours of the day led to suppression of pollutants close to surface and thus, an increase in ozone concentrations was observed. Low wind speeds played a major role in the increase of pollution levels in the region. HYSPLIT model is applied to some particular episodes and the results show that the northeasterly transport to the region was dominant, especially in the early-morning maximums.     

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.     

An Integrated Assessment Model for Fine Particulate Matter in Europe

Exposure to fine particles in the ambient air is recognized as a significant threat to human health. Two pathways contribute to the particle burden in the atmosphere: Fine particles originate from primary emissions, and secondary organic and inorganic particles are formed from the gas phase from the emissions of 'conventional' pollutants such as SO₂, NO_x, VOC and NH₃. Both types of particulate matter can be transported over long distances in the atmosphere. An integrated assessment model for particulate matter developed at IIASA addresses the relative importance of the different types of particulates, distinguishing primary and secondary particles and two size fractions. The model projects these emissions into the future and seeks cost-effective strategies for reducing health risks to population. The model integrates the control of primary emissions of fine particles with strategies to reduce the precursor emissions for the secondary aerosols. Preliminary results addressing the PM_2.5 fraction of both primary and secondary particulate matter indicate that in Europe the exposure to particulates will be significantly reduced as a side effect of the emission controls for conventional air pollutants (SO₂, NO_x, NH₃).     

Influence of Agricultural Land Use and Management on the Contents of Polycyclic Aromatic Hydrocarbons in Selected Silty Soils

The characteristics of transport and transformation of SO₂, NO_x and O₃ in northeast Asia have been investigated by using a comprehensive regional air quality model (RAQM) driven by a meteorological model MM5. A study period of 1-15 March 2002 has been selected due to the availability of intense observation of chemical species for both ground and upper levels. Model results have been compared against observational data to provide insights into the strength and weakness of the model’s ability and the evolutionary features of chemical species. Validation shows a good skill of this model system in reproducing most of the key features in long-range transport, but apparent bias still remains due to a series of uncertainties from either emission estimates, prescribed parameters, or inherent model limitations. In general, this model shows a better skill for SO₂ and O₃ than for NO_x. Large discrepancy occurs between the observed and calculated NO_x concentration at higher levels, with the model results being much lower. A series of sensitivity tests have been conducted to investigate the potential affecting factors and it is found that the inaccuracy or incompleteness in currently used emission inventories could be a most likely cause for such discrepancy. Long-range transport from Asian continent to the western Pacific is pronounced in springtime. Substantially high concentrations of SO₂ and NO_x in or above the boundary layer (0.5～3.0 km) over the Yellow Sea suggest an important pathway for long-range transport in northeast Asia.     

Development of a Multi-Resolution Emission Inventory and Its Impact on Sulfur Distribution for Northeast Asia

Emissions in East Asia for 1993 by administrative units and source types are estimated to support regional emission assessments and transport modeling studies. Total emission of SO_x, NO_x, soil NO_x, N₂O, and NH₃ are 24 150, 12 610, 1963, 908, and 8263 kton yr^-1, respectively.China's emission contribution is the highest for every species.The area sources are the most significant source type for SO_x and NO_x, but the fraction due to mobile source is highest for NO_x. Major LPSs are located from the middle to the east part of China, south and middle-west part of South Korea, and the east part of Japan. The area sources of SO_x show a pattern similar to population density, whereas NH₃ shows a strong landuse dependency. Detail emissions analysis reveals higher SO_x emission `cores' within each province. The estimated emissions are used to estimate sulfur deposition in the regions. The seasonal average sulfur distribution amounts are estimated from the ATMOS2 chemical transport model. The results showed anti-correlation with temperature for sulfur (SO₂ + SO₄ ^-2) concentrations and a positive correlation with rainfall for deposition.     

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.     

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.     

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.     

A Module to Calculate Primary Particulate Matter Emissions and Abatement Measures in Europe

Primary particulate matter is emitted directly into the atmosphere from various anthropogenic and natural sources such as power plants (combustion of fossil fuels) or forest fires. Secondary particles are formed by transformation of SO₂, NO_x, NH₃, and VOC in the atmosphere. They both contribute to ambient particulate matter concentrations, which may have adverse effects on human health. Health hazards are caused by small particulate size, high number of especially fine (< 2.5 µm) and ultra-fine (< 0.1 µm) particles and/or their chemical composition. As part of an integrated assessment model developed at IIASA, a module on primary particulate matter (PM) emissions has been added to the existing SO₂, NO_x, NH₃ and VOC sections. The module considers so far primary emissions of total suspended particles (TSP), PM₁₀ and PM_2.5 from aggregated stationary and mobile sources. A primary PM emission database has been established. Country specific emission factors for stationary sources have been calculated within the module using the ash content of solid fuels.     

A Computational Approach Based on GIS Technology for the Development of an Anthropogenic Emission Inventory of Gaseous Pollutants in Greece

This paper describes a computational system developed for the compilation of an anthropogenic emission inventory of gaseous pollutants for Greece. The inventory was developed using a geographical information system integrated with SQL programming language to provide high temporal gridded emission fields for CO, NO₂, NO, SO₂, NH₃ and 23 non-methane volatile organic compounds (NMVOCs) species for the reference year 2003. Activity and statistical data from national sources were used for the quantification of emissions from the road transport, the other mobile sources and machinery sectors and from range activities using top-down or bottom-up methodologies. Annual emission data from existing national and European emission databases were also used. The emission data were spatially and temporally disaggregated using source-specific spatiotemporal indicators. On national scale, the road transport sector produces about 60% of the annual CO and NMVOC total emissions, with gasoline vehicles being the main CO and NMVOC emissions source. The road transport is responsible for approximately half of the higher alkanes and for more than half of the ethene and toluene emissions. The maritime sector accounts for about 40% of the annual total NO_x emissions, most of which are emitted by the international shipping subsector, whilst SO₂ is emitted mainly by the energy sector. The evaluation of the emissions inventory suggests that it provides a good representation of the amounts of gaseous pollutants emitted on national scale and a good characterisation of the relative composition of CO and NO_x emission in the large urban centres.     

Effect of water vapor and nitrogen oxides upon the ozone layer

A theoretical meridional model of the O₃ layer is presented. Two-dimensional transport by eddies and mean motion is considered together with photochemical reactions involving O, N, and H. The model is used to evaluate the effect of increased contents of H₂O and NO_x in the stratosphere. It is found that a doubling of stratospheric humidity will reduce the total amount of O₃ by less than 1 %, while a doubling of NO_x will result in an 18 % reduction for middle latitudes and summer. A 10 % increase in NO_x will reduce the total O₃ by about 2.8%. The relations between UV radiation and total O₃ are described, in particular, for wavelengths of biological interest (290 to 320 nm). A 1% decrease in total O₃ will result in a 2 % increase in erythemogenic UV radiation.     

Calculating nitrogen deposition in Europe

Nitrogen deposition calculations for Europe were performed by separate models describing the long-range transport of ammonia and oxidized N. A linearized version of a non-linear atmospheric chemistry model was used for calculating oxidized N. Model computations were found to be consistent with the observed spatial pattern of wet nitrate deposition in Europe. Interannual meteorological variability was estimated to cause a typical year-to-year variation in annual oxidized N deposition of about 6 to 10%. Nitrogen deposition was computed for several NO _x emissions reduction scenarios. These scenarios were derived from an OECD study and applied to the 27 largest countries in Europe. Most reduction scenarios affected the deposition pattern of oxidized N, but the most extreme NO _x emission reduction scenario did not change very much the overall pattern of total (oxidized N plus ammonia N) N deposition. Depending on the desired level of environmental protection, it may be necessary to reduce ammonia emissions in addition to NO _x emissions in order to reduce N deposition in 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.     

Rural O3 Levels in the Middle Ebro Basin During the Plant Growing Season

Ground-level dynamics of O₃, NO _x and benzene, toluene, ethylbenzene and xylenes were characterised at rural sites in the medium Ebro River Basin (Northern Spain) from April to September (2003–2007) and by means of automated and passive monitoring. The study registered high O₃ levels within the area, which were influenced by traffic emissions, and a monthly evolution of these levels consistent with the occurrence of a broad summer maximum, typical of polluted areas. The mean ozone concentration registered in the studied area by means of passive sampling was 87?±?12 μg m^?3. The 2008/50/EC objective value for the protection of vegetation was widely exceeded during this study (AOT40?=?57,147?±?14,114 μg m^?3 h), suggesting that current ambient levels may pose a risk for crops and vegetation in this important agroindustrial region.