Photochemical Smog Formation Research Articles

A kinetic model for the prediction of no emissions from staged combustion of pulverized coal

Emissions of nitrogen oxides from coal combustion are a major environmental problem because they have been shown to contribute to the formation of acid rain and photochemical smog. Air staging and the application of low-NO x burners are effective in reducing the in-furnace-formed NO x . Fuel staging, or reburning, is another effective method to reduce NO x emissions in the combustion chamber. For a successful application of these processes on industrial scale, the governing parameters must be evaluated very carefully. Computer modeling is an efficient tool for acquiring a better knowledge of the optimum process parameters. In order to predict NO emissions from furnaces operated with advanced combustion technologies, a knowledge of the fate of coal nitrogen during the combustion process is paramount. An advanced NO x model for staged combustion of pulverized coal is presented. It is closely connected to a coal combustion model that includes primary pyrolysis and secondary reactions of tars formed during primary pyrolysis. The present NO x model takes in to account the different pathways of coal nitrogen release during primary and secondary pyrolysis, char, and soot combustion. The subsequent conversions of nitrogen-containing species comprise formation of NO from fuel nitrogen and air nitrogen (thermal NO) as well as reduction of NO by hydrocarbon and NH i radicals, char, and soot. The interaction between turbulence and chemistry is modeled by an advanced eddy dissipation concept (EDC). The NO x model is used to predict NO profiles that are compared to measurements obtained from combustion tests carried out at a bench-scale entrained-flow reactor. Comparisons are made for air-staged and fuel-staged combustion of pulverized coal using methane and coal as reburn fuel.

Enthalpies of Formation and Group Additivity of Alkyl Peroxides and Trioxides

Alkyl peroxides, trioxides, and the corresponding radicals are important in atmospheric chemistry, photochemical smog formation, and combustion processes, but accurate and widely accepted enthalpy data for these species are not available. In this work we verify enthalpy data for several compounds and derive the corresponding group values for use in the group additivity method. Isodesmic reactions and ab initio calculations (MP4SDTQ/6-31G*//MP2/6-31G* and G2) are used to determine enthalpies of formation for the following compounds (in kcal mol-1): CH3OOH (−31.8), C2H5OOH (−39.9), iPrOOH (iPr = (CH3)2CH−, −49.0), (CH3)3COOH (tBu = (CH3)3C−, −58.4), iPrOO• (−15.1), tBuCOO• (−25.2), CH3OOCH3 (−31.0), C2H5OOC2H5 (−47.2), iPrOOiPr, (−65.4), tBuOOtBu (−84.2), HOOOH (−23.0), CH3OOOH (−22.2), CH3OOOCH3 (−21.4). Our results on isodesmic reactions indicate that group additivity is an accurate method to estimate enthalpies (ΔHf°298 ) of alkyl peroxides and trioxides. Bond enthalpies are determined as follows: HOOO−H (82.6), CH3O2−H (86.6), C2H5O2−H (86.1), iPrO2−H (86.0), tBuO2−H (85.3), HOO−OH (35.8), CH3O−OCH3 (38.8), CH3OO−OH (34.2), CH3O−OOH (29.6), CH3O−OOCH3 (28.0), iPr−OO (36.6), tBu−OO (37.5). The recommended enthalpy group values of (O/C/O) and (O/O2) are −5.5 and 9.6 kcal mol-1, respectively.

Kinetics of the Reactions of Propionylperoxy Radicals with NO and NO2: Peroxypropionyl Nitrate Formation under Laboratory Conditions Related to the Troposphere

Peroxyacyl nitrates [RC(O)OONO2] are formed in the atmosphere in the oxidative degradation of many organic compounds of both anthropogenic and biogenic origin. They are important oxidant components of photochemical smog and can cause eye irritation and plant damage. Moreover, peroxyacyl nitrates act as temporary reservoirs for reactive intermediates involved in photochemical smog formation, and they play an important role in the transport of NOx in the troposphere. It is therefore essential to establish reliable data on the kinetics and mechanisms of their formation and removal for inclusion in models of atmospheric chemistry. The kinetic data base for the most atmospherically abundant of the series, acetylperoxy nitrate [CH3C(O)OONO2, PAN], is quite well established, but data are lacking for the higher homologues, e.g., peroxypropionyl nitrate [CH3CH2C(O)O2NO2, PPN], which has also been detected in the troposphere. Here we report data on a relative rate study of the reactions CH3CH2C(O)O2· + NO2 + M → CH...

HUMAN ALTERATION OF THE GLOBAL NITROGEN CYCLE: SOURCES AND CONSEQUENCES

Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many terrestrial, freshwater, and marine ecosystems. Many of the original plant species living in these ecosystems are adapted to, and function optimally in, soils and solutions with low levels of available nitrogen. The growth and dynamics of herbivore populations, and ultimately those of their predators, also are affected by N. Agriculture, combustion of fossil fuels, and other human activities have altered the global cycle of N substantially, generally increasing both the availability and the mobility of N over large regions of Earth. The mobility of N means that while most deliberate applications of N occur locally, their influence spreads regionally and even globally. Moreover, many of the mobile forms of N themselves have environmental consequences. Although most nitrogen inputs serve human needs such as agricultural production, their environmental consequences are serious and long term. Based on our review of available scientific evidence, we are certain that human alterations of the nitrogen cycle have: approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; increased concentrations of the potent greenhouse gas N2O globally, and increased concentrations of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth; caused losses of soil nutrients, such as calcium and potassium, that are essential for the long-term maintenance of soil fertility; contributed substantially to the acidification of soils, streams, and lakes in several regions; and greatly increased the transfer of nitrogen through rivers to estuaries and coastal oceans. In addition, based on our review of available scientific evidence we are confident that human alterations of the nitrogen cycle have: increased the quantity of organic carbon stored within terrestrial ecosystems; accelerated losses of biological diversity, especially losses of plants adapted to efficient use of nitrogen, and losses of the animals and microorganisms that depend on them; and caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries.

Sensitivity analysis of a UV radiation transfer model and experimental photolysis rates of NO 2 in the atmosphere of Mexico City

Photolysis of key species such as nitrogen dioxide, ozone and aldehydes, are the elementary reactions leading to the formation of photochemical smog. Calculations and experimental measurements (in particular, nitrogen dioxide) of these key reactions are reported, as well as, the sensitivity of them to the ozone column, local albedo and properties of the urban aerosol layer in Mexico City. A radiation transfer model (RTM ), based on the delta-Eddington approximation, was used in the calculations. The results show the importance of providing local resolution for photolysis rates by considering different local conditions within the modeling domain of air quality models.

Global total ozone dynamics

A review has been made recently studying global total ozone changes (including stratospheric and troposphere components), as well as biologically active surface solar ultraviolet (UV-B) radiation variations on the basis of satellite and conventional surface observations (Kondratyev and Varotsos, Part I). In the aforementioned review, relevant impacts on terrestrial and aquatic ecosystems, as well as on biochemical cycles and man, have been discussed. Special attention has been paid to the analysis of observed and potential impacts of enhanced UV-B radiation on biogeochemical cycles and the chemical composition of the atmosphere. In this context, possibilities remote sensing techniques applications aimed at obtaining more complete information on atmospheric concentrations of various trace gases determining the ozone content have been considered in the present paper.An overview of the ozone issues is given including the following aspects: 1. The impact of tropospheric ozone on climate as a greenhouse gas (GHG), 2. Solar activity effects on TO and ozone concentration vertical profiles in both the troposphere and stratosphere (in cases of solar radiation absorption by the stratosphere, an unexpected problem arises via a coupling between processes of increased absorption due to "bursts" of solar activity and an enhanced destruction of ozone molecules due to the same increase resulting in weakening UV radiation absorption) and 3. Surface ozone concentration variations under conditions of polluted urban atmospheres which lead to episodes of photochemical smog formation (dangerous for human health).

Global total ozone dynamics

An overview of the ozone issues is given including the following aspects: 1. The impact of tropospheric ozone on climate as a greenhouse gas (GHG), 2. Solar activity effects on TO and ozone concentration vertical profiles in both the troposphere and stratosphere (in cases of solar radiation absorption by the stratosphere, an unexpected problem arises via a coupling between processes of increased absorption due to "bursts" of solar activity and an enhanced destruction of ozone molecules due to the same increase resulting in weakening UV radiation absorption) and 3. Surface ozone concentration variations under conditions of polluted urban atmospheres which lead to episodes of photochemical smog formation (dangerous for human health).

Numerical simulation of photochemical smog formation in Athens, Greece—A case study

High emission levels and the unfavourable topography are the main reasons for the alarming photochemical air pollution levels in Athens. An analysis of available air quality data proves that air pollution levels in Athens are largely affected by local wind circulation systems. The most frequent of these systems is dominated by the phenomenon of the sea breeze. Severe air pollution episodes occur, however, primarily under synoptic situations leading to stagnant conditions in the atmosphere over Athens. Photosmog formation in the Athens Basin is studied with the photochemical dispersion model MARS. The implicit solution algorithm incorporated in MARS is characterized by a variable time increment and a variable order. This solver allows avoiding unnecessary operator splitting by a coupled treatment of vertical diffusion and chemical kinetics. In this paper, MARS is used to analyse the situation on 25 May 1990, a day for which very high air pollution levels were reported in Athens. The simulation results elucidate the characteristics of a photosmog episode under stagnant conditions in Athens. In general, the model results reproduce satisfactorily the observed air pollution patterns.

On-Road Vehicle Emissions: Regulations, Costs, and Benefits

In 1990 Congress passed the Clean Air Act Ammendments, many parts of which deal with motor vehicles. Motor vehicles are the primary source of urban carbon monoxide and are an important source of hydrocarbons and oxides of nitrogen responsible for the formation of photochemical smog and ground-level ozone. Cost estimates for implementing the Acts`s mobil source provisions range up to $12 billion annually. Because of the huge economic cost affecting a ubiquitous transportation method, the authors analyse the scientific basis for the legistation programs. Their work is described here. They conclude that regulatory policies based on a computer model that targets all vehicles equally, with out recognizing the overriding importance of individual maintenance, may not be cost-effective or may be ineffective. 23 refs., 1 fig., 1 tab.

The EUMAC Zooming Model, a tool for local-to-regional air quality studies

The EUMAC Zooming Model (EZM) is a comprehensive model system for simulations of wind flow and air pollutant transport and transformation at the local-to-regional scale. Core models of the EZM are the nonhydrostatic mesoscale model MEMO and the photochemical dispersion model MARS. Manifold air quality studies, primarily for large urban agglomerations, have been already performed with the EZM. In most of these studies the results of the EZM agree fairly well with available observations. An example for a successful study with the EZM is its application to simulate the formation of photochemical smog in the case of stagnant meteorological conditions in Athens. By applying a suitable nesting technique, MEMO reproduces satisfactorily the observed diurnal wind pattern in Athens. The results of MARS elucidate the characteristics of a severe photosmog episode in Athens and are in general very similar to available observations.

The relative tolerance of some Eucalyptus species to ozone exposure

Surface ozone (O3) concentrations have proved to be difficult to control and regional (03) concentrations appear to be increasing in many parts of the world. Eucalyptus species are widely used as plantation trees in many regions that have Mediterranean, warm temperate and subtropical climates. An increased knowledge of the effects of tropospheric O3 on Eucalyptus trees may assist in the management of these plantations. The present study was set up to evaluate injury and measure growth reduction caused by O3 in eight Eucalyptus species. Seven month old saplings were exposed to diumally varied concentrations of 26 or 172 nil−1 (03) (7h mean) 7h day−1, 5 days in every 14 days, for 18 weeks. The plants were grown in open top field chambers fitted with rain excluders. Significant differences were found between the responses of different species. There was no visible injury or dry weight reduction in E. globulus. However O3 exposure caused a 30% weight reduction and 90% leaf injury in E. microcorys. E. gomphocephala also experienced a 30% weight reduction but no significant leaf injury. Hence Eucalyptus plantations in regions with the potential for photochemical smog formation, such as some of the rapidly developing industrialising nations in Asia and South America, will need to consider O3 tolerance when selecting plantation trees.

Seasonal behavior of tropospheric ozone in the Sao Paulo (Brazil) metropolitan area

This paper presents a study of the seasonal behavior of tropospheric ozone and its precursors in the Sao Paulo Metropolitan Area as observed during 1987. The 03, NO, NO 2, NMHC, and meteorological data were collected at an air quality station in downtown Sao Paulo by the State Environmental Protection Agency (CETESB). The air pollutant measurements were related to both daily total insolation and the number of hours of insolation measured at the Sao Paulo University Climatological Station. Correlations between both radiation parameters and total daily integrated ozone amounts were performed. The total number of sunshine hours was highly correlated to mean hourly ozone concentration values during each month of 1987. The seasonal behavior of NO, NO 2, and NMHC was also studied. Two diurnal peaks in average NO concentration were observed, i.e. one in early morning and one in early evening; both were due to emissions from urban mobile sources. The magnitude of these peaks doubled in value during the winter months. Its diurnal concentration variation was inverse to that of the 03; similar behavior was found for NO 2 and for NMHC. The data presented herein show the influence of solar radiation and of ozone precursors on photochemical smog formation in this tropical region.

High resolution gas chromatographic determination of the atmospheric reactivity of engine‐out hydrocarbon emissions from a spark‐ignited engine

AbstractThe reactivities of engine‐out exhaust hydrocarbon (HC) emissions in photochemical smog formation have been determined for three fuels (isooctane, an aromatic blend, and a gasoline) in a single‐cylinder, spark‐ignited engine. High resolution capillary GC was used to determine the mole fractions of the exhaust hydrocarbon species. Temperature programmed chromatography on a single capillary column was sufficient to separate the major exhaust species. A library of approximately 160 hydrocarbon species was used to identify typically 90–95 % of the HC species present. GC‐MS was used selectively to verify peak assignments.The effect of engine operating parameters (fuel‐to‐air ratio, spark timing, and speed) on reactivity was examined. Engine operating parameters affect both total emissions [g/mile] and the specific atmospheric reactivity [g ozone/g HC emissions] of these emissions. Changing the operating parameters to control total emissions may not be as effective as expected in controlling the total reactivity [g ozone/mile] of the emissions because the specific reactivity can also change simultaneously. Effects of changes in operating parameters differ significantly as the type of fuel is varied. The ability to measure exhaust hydrocarbon species emissions accurately and quickly will increase in importance as reactivity‐based emissions standards come into widespread use.

Measurement of the Taiwan Ambient Trace Gas Concentration by Kilometer-Pathlength Fourier-Transform Infrared Spectroscopy

A portable open long-path Fourier-transform infrared system (POPFT-IR) operable at pathlengths of up to 961m has been constructed for the detection and measurement of trace gases in ambient air and for photochemical smog formation studies. The long optical path is achieved by using a three-mirror multiple reflection cell with a 15.5m base path. The combination of a retro-reflection mirror with one of three mirrors eliminates any air-turbulence interference. The design, construction, advantage, and use of this novel folded open-path optical system and calibration spectrum for quantitative analysis are described in detail. Preliminary ambient air measurements were made at a variety of locations in Taiwan from urban, suburban and rural to remote areas. The existing trace gases in the background atmosphere were measured as nitrous oxide (N2O), methane (CH4), carbon monoxide (CO) and carbon dioxide (CO2). Major pollutants such as ethylene (C2H4), propylene (C3H6), ammonia (NH3), ozone (O3) and peroxyacetyl nitrate (PAN) were measured in the polluted urban atomosphere.

Assessment of the atmospheric hazards and risks of new chemicals: Procedures to estimate “hazard potentials”

Before introduction new chemical substances are evaluated on their potential hazards and risks. Concerning the assessment of atmospheric hazards and risks the direct effects caused by exposure to the new chemicals and indirect effect caused by deposition to soil and surface water are accounted for in assessment systems. However, the potential impact of new chemicals on atmospheric processes is generally not included. In this paper procedures to estimate “hazard potentials” to quantify the potential risk of a new substance in atmosphere-related environmental problems are proposed and discussed. In particular, hazard potentials for the following topics are defined: • ∗ global warming; • ∗ ozone depletion; • ∗ photochemical smog formation; • ∗ acidification and eutrophication. Based on these “hazard potentials” atmospheric hazards and risks can be assessed.

Applications of electron spin resonance to environmental problems

A selective review is given of some e.s.r investigations related to problems of environmental concern including ozone depletion, photochemical smog formation, and acid deposition.

Use of carbon adsorption traps combined with high resolution gas chromatography – mass spectrometry for the analysis of polar and non‐polar C4‐C14 hydrocarbons involved in photochemical smog formation

AbstractA method has been developed for the collection and analysis of polar and non‐polar C4‐C14 hydrocarbons involved in the formation of photochemical smog. Enrichment of hydrocarbons from both polluted and unpolluted areas has been achieved with three‐stage traps packed with carbon adsorbents of different surface area; the use of a home‐made desorption unit employing cryofocusing then enables the determination of the compounds by HRGC‐FID. Two‐stage traps filled with graphitic carbon have been used prior to GC‐MS identification and quantitation of compounds producing overlapping peaks.The methodology has been tested in the urban area of Rome and in a pine forest, and more than 140 different compounds identified and quantitated. Many of the constituents were found to be oxygenated, either formed by photochemical reactions or of anthropogenic origin.

A field study of photochemical smog formation under stagnant meteorological conditions

Photochemical air pollution episodes during 15–20 July 1981, covering the Tokyo Metropolitan Area under the stagnant meteorological conditions, were analyzed. Three-dimensional (3-D) pollutant and meteorological observations showed that polluted air masses followed sea and land breeze circulation patterns. Aged secondary pollutants were detected aloft from midnight until early morning. These pollutants subsequently entrained into the daytime mixed layer and affected O 3 formation. To understand this stagnating system, a simple trajectory model was used. Simulated results showed good qualitative agreement with observations, but the model overestimated the surface concentration and underestimated the aircraft observations. This was mainly caused by the assumption of vertical uniformity within the model.

Solid NaCI can affect atmospheric chemistry

At a symposium sponsored by the Physical Chemistry Division at the Los Angeles meeting of the American Chemical Society, California chemists offered data showing that solid sodium chloride is not an inert contributor to the chemistry of atmospheres. Instead, chloride ions from solid sodium chloride, through a variety of reactions, can be converted to photochemically reactive forms and these labile forms may play major roles in the photochemistry of polluted marine areas. As Barbara J. Finlayson-Pitts, principal investigator and professor of chemistry at California State University, Fullerton, explains: If these kinds of reactions occurred in polluted marine areas, what you would do is basically give photochemical smog formation a little kick to get it started in the morning, much in the same way as the hydroxyl radical does. She and her coworkers have shown that gaseous dinitrogen pentoxide (N 2 O5 ) and chlorine nitrate (CIONO 2 ) react with solid sodium chloride to yield, respectively, nitryl chloride...

Continuous atmospheric measurements of peroxyacetyl nitrate (Pan) in a Mediterranean site (Athens, greece)

Abstract Photochemical pollution episodes are becoming an important problem for many major Mediterranean cities with a hot, sunny climate. Peroxyacetyl nitrate (PAN) can serve as a very good tracer of photochemical activity in the atmosphere, and was measured automatically for the first time in Athens, Greece, during the period 18 September‐10 October 1985. The observed overall PAN concentrations were generally lower than expected for a city with frequent formation of photochemical smog. It appears, however, that elevated PAN and ozone concentrations occur mainly by sea‐breeze circulation, which is often observed at coastal sites.