Numerical model evaluation of the extension of the critical dividing streamline hypothesis to mesoscale two-dimensional terrain

A two-dimensional nonlinear numerical model is used to study the extension of the critical dividing streamline hypothesis to larger scale terrain than considered in most previous observational studies. Upstream blocking in the absence of thermal forcing is found to be reasonably well described for air quality assessment purposes by the critical dividing streamline hypothesis. The effect of rotation (i.e. the Coriolis force) is to decrease the extent of blocking in marginal cases. Influence of the Coriolis force is expected to increase as the length scale of the topography increases.It is also found that thermally induced nocturnal slope winds may compromise the dividing streamline hypothesis as a result of their entrainment mass flux. We suggest that slope flows have not played a substantial role in previous tracer studies over small-scale terrain due to the dependence of slope flows on length scale and ambient thermal stratification. Tracer studies around mesoscale terrain would help to clarify the importance of rotational and diabatic effects.     

Assessment of the nested grid model estimates for driving regional visibility models in the southwestern United States

The Nested Grid Model (NGM) is a primitive-equation meteorological model that is routinely exercised over North America for forecasting purposes by the National Meteorological Center. While prognostic meteorological models are being increasingly used to drive air quality models, their use in conducting annual simulations requires significant resources. NGM estimates of wind fields and other meteorological variables provide an attractive alternative since they are typically archived and readily available for an entire year. Preliminary evaluation of NGM winds during the summer of 1992 for application to the region surrounding the Grand Canyon National Park showed serious shortcomings. The NGM winds along the borders between California, Arizona and Mexico tend to be northwesterly with a speed of about 6 m/sec, while the observed flow is predominantly southerly at about 2-5 m/sec. The mesoscale effect of a thermal low pressure area over the highly heated Southern California and western Arizona deserts does not appear to be represented by the NGM because of its coarse resolution and the use of sparse observations in that region. Tracer simulations and statistical evaluation against special high resolution observations of winds in the southwest United States clearly demonstrate the northwest bias in NGM winds and its adverse effect on predictions of an air quality model. The "enhanced" NGM winds, in which selected wind observations are incorporated in the NGM winds using a diagnostic meteorological model provide additional confirmation on the primary cause of the northwest bias. This study has demonstrated that in situations where limited resources prevent the use of prognostic meteorological models, previously archived coarse resolution wind fields in which additional observations are incorporated to correct known biases provide an attractive option.     

Assessment of the Nested Grid Model Estimates for Driving Regional Visibility Models in the Southwestern United States

ABSTRACT

The Nested Grid Model (NGM) is a primitive-equation meteorological model that is routinely exercised over North America for forecasting purposes by the National Meteorological Center. While prognostic meteorological models are being increasingly used to drive air quality models, their use in conducting annual simulations requires significant resources. NGM estimates of wind fields and other meteorological variables provide an attractive alternative since they are typically archived and readily available for an entire year. Preliminary evaluation of NGM winds during the summer of 1992 for application to the region surrounding the Grand Canyon National Park showed serious shortcomings. The NGM winds along the borders between California, Arizona and Mexico tend to be northwesterly with a speed of about 6 m/sec, while the observed flow is predominantly southerly at about 2-5 m/sec. The mesoscale effect of a thermal low pressure area over the highly heated Southern California and western Arizona deserts does not appear to be represented by the NGM because of its coarse resolution and the use of sparse observations in that region. Tracer simulations and statistical evaluation against special high resolution observations of winds in the southwest United States clearly demonstrate the northwest bias in NGM winds and its adverse effect on predictions of an air quality model. The “enhanced” NGM winds, in which selected wind observations are incorporated in the NGM winds using a diagnostic meteorological model provide additional confirmation on the primary cause of the northwest bias. This study has demonstrated that in situations where limited resources prevent the use of prognostic meteorological models, previously archived coarse resolution wind fields in which additional observations are incorporated to correct known biases provide an attractive option.     

Effect of non-zero divergence wind fields on atmospheric transport calculations

The use of wind fields that do not satisfy the equation of continuity exactly can introduce significant errors in the calculation of the atmospheric transport of chemical species. Results are presented showing that non-zero divergence winds, used as inputs to a transport equation of conservation form, can introduce local fictitious production or destruction rates into the numerical calculations. A divergence-corrected form of the equation, which is mathematically equivalent but not numerically equivalent to an advection form of the equation, can eliminate these undesirable effects as well as the advection form equation can. The divergence-corrected form of the equation leads exactly to the conservation form when massconsistent winds are used. Also, it has the desirable property that the numerical form can preserve, to a large extent, integral conservation relations of the original mass balance equation even when Δ ·V ≠ 0. The effects of using non-zero divergence winds appear as first-order chemical reactions. These terms are compared quantitatively with the rates of several tropospheric chemical reactions.     

Variable K-theory model for the dispersion of air pollutants in low-wind conditions in the surface-based inversion

A variable K-model has been proposed for the dispersion in low winds in the surface-based inversion by expressing the eddy diffusivities as a linear function of downwind distance from the source. The resulting partial differential equation with variable coefficients along with the physically relevant boundary conditions is solved analytically. For the accuracy of the so-obtained solution, an analysis of the convergence and error estimation has been carried out. It is shown that the series converges absolutely. An upper bound for the error based on the partial sum of the series is estimated and it is described that the error tends to zero as the number of terms in the expansion are sufficiently large.The solution has been used to simulate the field tracer data sets collected from Hanford and IIT diffusion experiments in stable and unstable conditions, respectively. It predicts 41% cases in stable and 35% cases in unstable conditions within a factor of two to observations.     

Ozone and grosswetterlagen

Meteorological conditions have a decisive impact on surface ozone concentrations. In this study, an empirical model is used to explain the interdependence of ozone and grosswetterlagen. Different meteorological parameters such as air temperature, global solar radiation, relative humidity, wind direction and wind speed are used. Additional nitric oxide (NO) was taken as a representative for the emission situation and ozone maximum of the preceding day in order to evaluate the development of the photochemical situation. The dataset includes data collected over a period of three years (1992–1994) from three stations outside of Munich and one in the center of Munich. All values become variables by calculating means, sums or maxima of the basic dataset consisting of half-hour means. Seasonal periodicity of data is detected with Fourier analysis and eliminated by a division method after computing a seasonal index. The dataset is divided into three different grosswetterlagen groups, depending on main wind direction. One mostly cyclonic (westerly winds), onemixed (alternating winds) and one onlyanticyclonic (easterly winds). The last is completed with one summertime group including values from April to August. Factor analysis is performed for each group to obtain independent linear variable combinations. Overall, relative humidity is the dominant parameter, a typical value indicating meteorological conditions during a grosswetterlage. Linear multiple regression analysis is performed using the factors obtained to reveal how the ozone concentrations are explained in terms of meteorological parameters and NO. The results improve from cyclonic to anticyclonic grosswetterlagen in conformance with the increasing significance of photochemistry, indicated by the high solar radiation and high temperature, and the low relative humidity and low wind speed. The explained variance r² reaches its maximum with more than 50 % of the time in Munich center. This empirical model is applicable to the forecasting of local ozone maximum concentrations with a total standard error deviation of 8.5 to 12.8 % and, if ozone concentrations exceed 80 ppb, with a standard error deviation of 5.4 to 9.5 %.     

Ozone and grosswetterlagen

Meteorological conditions have a decisive impact on surface ozone concentrations. In this study, an empirical model is used to explain the interdependence of ozone and grosswetterlagen. Different meteorological parameters such as air temperature, global solar radiation, relative humidity, wind direction and wind speed are used. Additional nitric oxide (NO) was taken as a representative for the emission situation and ozone maximum of the preceding day in order to evaluate the development of the photochemical situation. The dataset includes data collected over a period of three years (1992–1994) from three stations outside of Munich and one in the center of Munich. All values become variables by calculating means, sums or maxima of the basic dataset consisting of half-hour means. Seasonal periodicity of data is detected with Fourier analysis and eliminated by a division method after computing a seasonal index. The dataset is divided into three different grosswetterlagen groups, depending on main wind direction. One mostly cyclonic (westerly winds), one mixed (alternating winds) and one only anticyclonic (easterly winds). The last is completed with one summertime group including values from April to August. Factor analysis is performed for each group to obtain independent linear variable combinations. Overall, relative humidity is the dominant parameter, a typical value indicating meteorological conditions during a grosswetterlage. Linear multiple regression analysis is performed using the factors obtained to reveal how the ozone concentrations are explained in terms of meteorological parameters and NO. The results improve from cyclonic to anticyclonic grosswetterlagen in conformance with the increasing significance of photochemistry, indicated by the high solar radiation and high temperature, and the low relative humidity and low wind speed. The explained variance r² reaches its maximum with more than 50 % of the time in Munich center. This empirical model is applicable to the forecasting of local ozone maximum concentrations with a total standard error deviation of 8.5 to 12.8 % and, if ozone concentrations exceed 80 ppb, with a standard error deviation of 5.4 to 9.5 %.     

Optical characteristics of southeast Asia's regional aerosols and their sources

The dominant optical characteristics of Southeast Asia (SEA)'s regional aerosols were determined from the cluster analysis of the 26 AERONET aerosol inversion products, including aerosol light scattering/absorption indicators and aerosol size/shape parameters retrieved from 2003 to 2007. The data sets were acquired from four stations: Bac Giang in Vietnam and Mukdahan, Pimai, and Silpakorn University in Thailand. The cluster analysis showed agreement among the aerosol optical characteristics, land cover/uses, season as the surrogate of the prevailing winds, and observations from the literature. The results of this study showed that during the northeast prevailing winds from mid-September to December, the high aerosol exposure events were most frequently observed over the upwind station and less often over the downwind stations. This aerosol exhibited a single scattering albedo (SSA) of approximately 0.95 (440 nm), a relatively low refractive index, and a larger fine-mode size, suggesting it had the characteristics of urban/industrial aerosols reported in the literature. These aerosol sources were upwind from Bac Giang, probably in eastern China. From January to April, the aerosol exhibited a lower SSA of approximately 0.90, a higher refractive index, and a smaller fine-mode size, suggesting biomass burning smoke reported in the literature. The SEA urban aerosol exhibited a mean SSA of approximately 0.90 (440 nm) or lower, and the coarse-mode aerosol, possibly road dust or soil dust, played a role from October to January when seasonal winds are strongest. The results from a canonical discriminant function analysis suggest that the dominant SEA aerosol clusters tended to be separated by a canonical function positively correlated with SSA, the fine-mode asymmetry factor, and the overall fine-mode size and negatively correlated with the refractive index.     

A complex terrain dispersion model for regulatory applications at the Westvaco luke mill

A data set for studying transport and dispersion in complex terrain was collected at the Westvaco Corporation's Luke Mill, located in the Potomac River valley in western Maryland. Meteorological analyses indicate very strong channeling of winds and the presence of strong inversions and wind shears in a shallow layer at the height of the surrounding mountaintops (300 m above the valley floor). Wind velocities observed near the valley floor are unrepresentative of wind velocities at plume height. Observed turbulence intensities at plume height are about twice as large as those observed over flat terrain. Standard stability classification schemes generally underestimate plume dispersion at this site. When high 3-h and 24-h average SO₂ concentrations are observed, winds are usually light and an inversion is present. These instances of relatively high concentrations are often associated with periods when the wind shifts direction 180° from up-valley to down-valley or vice versa, and the nearly stagnant polluted air mass blows against the mountainsides.A dispersion model was developed that is Gaussian in form but uses observed meteorological data to the maximum extent possible. For example, observed turbulence intensities at plume height are used to estimate dispersion. Plume impaction on terrain is calculated if the plume height is below a critical height dependent on the Hill Froude number. Evaluation of the model with the full 2-y data set shows that it can estimate the second highest 3-h and 24-h average concentrations (of regulatory significance) with a mean bias of less than 7%.     

A life-cycle comparison of alternative automobile fuels

We examine the life cycles of gasoline, diesel, compressed natural gas (CNG), and ethanol (C2H5OH)-fueled internal combustion engine (ICE) automobiles. Port and direct injection and spark and compression ignition engines are examined. We investigate diesel fuel from both petroleum and biosources as well as C2H5OH from corn, herbaceous bio-mass, and woody biomass. The baseline vehicle is a gasoline-fueled 1998 Ford Taurus. We optimize the other fuel/powertrain combinations for each specific fuel as a part of making the vehicles comparable to the baseline in terms of range, emissions level, and vehicle lifetime. Life-cycle calculations are done using the economic input-output life-cycle analysis (EIO-LCA) software; fuel cycles and vehicle end-of-life stages are based on published model results. We find that recent advances in gasoline vehicles, the low petroleum price, and the extensive gasoline infrastructure make it difficult for any alternative fuel to become commercially viable. The most attractive alternative fuel is compressed natural gas because it is less expensive than gasoline, has lower regulated pollutant and toxics emissions, produces less greenhouse gas (GHG) emissions, and is available in North America in large quantities. However, the bulk and weight of gas storage cylinders required for the vehicle to attain a range comparable to that of gasoline vehicles necessitates a redesign of the engine and chassis. Additional natural gas transportation and distribution infrastructure is required for large-scale use of natural gas for transportation. Diesel engines are extremely attractive in terms of energy efficiency, but expert judgment is divided on whether these engines will be able to meet strict emissions standards, even with reformulated fuel. The attractiveness of direct injection engines depends on their being able to meet strict emissions standards without losing their greater efficiency. Biofuels offer lower GHG emissions, are sustainable, and reduce the demand for imported fuels. Fuels from food sources, such as biodiesel from soybeans and C2H5OH from corn, can be attractive only if the co-products are in high demand and if the fuel production does not diminish the food supply. C2H5OH from herbaceous or woody biomass could replace the gasoline burned in the light-duty fleet while supplying electricity as a co-product. While it costs more than gasoline, bioethanol would be attractive if the price of gasoline doubled, if significant reductions in GHG emissions were required, or if fuel economy regulations for gasoline vehicles were tightened.     

An examination of boundary layer structure under the influence of the gap winds in Urumqi, China, during air pollution episode in winter

Tethered-sonde measurements of atmospheric profiles were performed at Urumuqi, capital of the Xinjiang Uyghur Autonomous Region of China, from 29 December 2008 to 14 January 2009. The data were used to examine the boundary layer structure during this severe air pollution period. Diurnal evolution of local wind flow near Urumqi was simulated using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). Measurements from operational radiosonde data showed that a southeasterly elevated low-level jet often intruded upon Urumqi through the middle Tianshan Mountain pass to the south of the city. The tethered-sonde measurements showed that calm and northwesterly winds prevailed near the surface in Urumqi, whereas the southeasterly winds of relatively higher speed were dominant above approximately 400 m. Both temperature inversion and humidity inversion frequently occured during day and nighttime. Temperature inversion intensity could sharply rise as the stronger elevated southeasterly gale (ESEG) happened. Model simulations showed that the winds near the surface around Urumqi remained calm during nighttime and developed toward the mountains during daytime. As cool airflow in the basin confronted the southeasterly winds from the pass in the lower layer, they formed a convergence line around Urumqi city, which was not favor for dilution of air pollutants.     

Cooling Pond Steam Fog

This paper is responsive to needs to describe and predict the environmental effects from power plant cooling ponds. A study was made to determine atmospheric and pond surface conditions required for steam fog to occur from power plant cooling ponds, to define the dimensions of the fog, and to collect data on deposition of ice. Data, collected principally at the 4-Corners Plant over a three-year period, included water surface temperature, ambient meteorological conditions and occurrence and magnitude of steam fog and ice deposition. With strong winds, the fog extended onshore without lifting. With light winds, the fog extended some distance onshore but then lifted to form stratus. With almost calm winds, the steam fog lifted over the pond and drifted downwind as stratus. Steam fog was observed in winds to 28 mph, air-water temperature differences from 21.5° to 68°F and in atmospheric stability categories C, D, E, and F. A fog index number, Ar/(e_s — e_a)°F/mbs, was defined and used for data interpretation, where Ar is temperature of water less temperature of ambient air, e_s is the saturation vapor pressure of the ambient air and e_a is the actual vapor pressure of the ambient air. The probability of occurrence of steam fog as a function of the fog index number varied from 0.04 for an index number less than 10 to 1.00 for an index number greater than 90. From the data, if fog occurred, its extent along the ground was ≥100 feet 88% of the time, ≥500 feet 35% of the time, ≥1000 feet 18% of the time, and ≥5000 feet 12% of the time. If stratus occurred its extent above ground was ≥1 mile 91% of the time, ≥5 miles 55% of the time and ≥10 miles 36% of the time. Measurements showed that steam fog droplet sizes predominate in the 10 micron diameter size. Values of liquid water content up to 0.20 g/m³ were reported. Ice accretion data show build-up rates from 0.23 to 13 mm/hr of rime.     

Synoptic weather patterns and their relationship to high ozone concentrations in the Taichung Basin

Frequent high ozone days (defined as daily maximum ozone concentration ⩾80 ppb) during recent years in the Taichung Basin have caused much concern. High ozone days occur mainly during autumn and spring. Statistically, there is no clear linear relationship between a single meteorological variable and ozone concentration. In this study, data from 1996–2000 has shown that high ozone concentrations occur during two types of synoptic weather patterns. The first type is a continental cyclone emanating from mainland China, the southern part of it swept towards Taiwan by easterly winds. The second pattern is a tropical depression moving northwards toward the region, the northern part of it affecting Taiwan via easterly winds. Both types cover Taiwan with easterly winds, which are blocked by the Central Mountain Ranges (altitude of 2000–3000 m). The ranges create lee cyclogenesis to the west, which is unfavorable for pollutant dispersion and leads to serious air pollution episodes.The statistical results of the synoptic weather patterns in relation to ozone concentrations are based on the 5 yr data (1996–2000). This was obtained from a network of air-pollution monitoring sites in the study area, while the vertical data come from two 3-day tethersonde experimental campaigns conducted during March and October 2000, measuring air pressure, air temperature, relative humidity, wind speed and direction, non-methane hydrocarbons, NO_x and O₃.     

Different splitting techniques with application to air pollution models

Splitting techniques are commonly used when large-scale models, which appear in different fields of science and engineering, are treated numerically. Four types of splitting procedures are defined and discussed. The problem of the choice of a splitting procedure is investigated. Several numerical tests, by which the influence of the splitting errors on the accuracy of the results is studied, are given. It is shown that the splitting errors decrease linearly when (1) the splitting procedure is of first order and (2) the splitting errors are dominant. Three examples for splitting procedures used in all large-scale air pollution models are presented. Numerical results obtained by a particular air pollution model, Unified Danish Eulerian Model (UNI-DEM), are given and analysed.     

Effects of wind direction on coarse and fine particulate matter concentrations in southeast Kansas

Field data for coarse particulate matter ([PM] PM10) and fine particulate matter (PM2.5) were collected at selected sites in Southeast Kansas from March 1999 to October 2000, using portable MiniVol particulate samplers. The purpose was to assess the influence on air quality of four industrial facilities that burn hazardous waste in the area located in the communities of Chanute, Independence, Fredonia, and Coffeyville. Both spatial and temporal variation were observed in the data. Variation because of sampling site was found to be statistically significant for PM10 but not for PM2.5. PM10 concentrations were typically slightly higher at sites located within the four study communities than at background sites. Sampling sites were located north and south of the four targeted sources to provide upwind and downwind monitoring pairs. No statistically significant differences were found between upwind and downwind samples for either PM10 or PM2.5, indicating that the targeted sources did not contribute significantly to PM concentrations. Wind direction can frequently contribute to temporal variation in air pollutant concentrations and was investigated in this study. Sampling days were divided into four classifications: predominantly south winds, predominantly north winds, calm/variable winds, and winds from other directions. The effect of wind direction was found to be statistically significant for both PM10 and PM2.5. For both size ranges, PM concentrations were typically highest on days with predominantly south winds; days with calm/variable winds generally produced higher concentrations than did those with predominantly north winds or those with winds from "other" directions. The significant effect of wind direction suggests that regional sources may exert a large influence on PM concentrations in the area.     

A study of surface ozone and the relation to complex wind flow in Hong Kong

Ozone measurements made from 5 sites in Hong Kong have been analyzed, including those from one upwind, one downwind, and three urban locales. The data are analyzed in terms of the seasonal and diurnal trends. A subset of data in autumn is further analyzed to study the relationship between the ozone spatial pattern and wind flow as well as other meteorological parameters. The results show that averaged ozone levels at most sites exhibit maxima in autumn, which appears to be a unique feature for eastern Asia. On average the daily maximum 1-h concentrations are found to be higher in the western (normally downwind) site than those on the eastern side and in urban areas. Examination of surface wind patterns and other meteorological parameters suggest that elevated ozone concentrations on the western side occur during the days with intense solar radiation, light winds, and in the presence of a unique wind circulation. The wind reversal in the western parts under the “convergence” flow is believed to be an important cause of the high-ozone events observed there. Such wind flow may re-circulate/transport nearby urban plumes (in this case the Hong Kong–Shenzhen urban complex). Examination of chemical data from the western site has shown that averaged afternoon SO₂ to NO_x ratios on days with wind reversal are larger than those of typical urban Hong Kong and that a significant SO₂ enhancement was clearly indicated on several occasions. The SO₂ enhancement may be interpreted as being the evidence to suggest the contribution of regional sources and/or Hong Kong’s power plants (both containing high SO₂). A case study has shown that when moderately strong northwesterly wind prevails, elevated ozone and SO₂ can be transported to western Hong Kong from the inner Pearl Delta region. This study has also indicated that under the impact of ENE winds the eastern side of Hong Kong is not frequently affected by the re-circulating ozone plumes present in the western side.     

Effects of Wind Direction on Coarse and Fine Particulate Matter Concentrations in Southeast Kansas

Abstract

Field data for coarse particulate matter ([PM] PM₁₀) and fine particulate matter (PM_2.5) were collected at selected sites in Southeast Kansas from March 1999 to October 2000, using portable MiniVol particulate samplers. The purpose was to assess the influence on air quality of four industrial facilities that burn hazardous waste in the area located in the communities of Chanute, Independence, Fredonia, and Coffeyville. Both spatial and temporal variation were observed in the data. Variation because of sampling site was found to be statistically significant for PM₁₀ but not for PM_2.5. PM₁₀ concentrations were typically slightly higher at sites located within the four study communities than at background sites. Sampling sites were located north and south of the four targeted sources to provide upwind and downwind monitoring pairs. No statistically significant differences were found between upwind and downwind samples for either PM₁₀ or PM_2.5, indicating that the targeted sources did not contribute significantly to PM concentrations. Wind direction can frequently contribute to temporal variation in air pollutant concentrations and was investigated in this study. Sampling days were divided into four classifications: predominantly south winds, predominantly north winds, calm/variable winds, and winds from other directions. The effect of wind direction was found to be statistically significant for both PM₁₀ and PM_2.5. For both size ranges, PM concentrations were typically highest on days with predominantly south winds; days with calm/variable winds generally produced higher concentrations than did those with predominantly north winds or those with winds from “other” directions. The significant effect of wind direction suggests that regional sources may exert a large influence on PM concentrations in the area.     

A Life-Cycle Comparison of Alternative Automobile Fuels

ABSTRACT

We examine the life cycles of gasoline, diesel, compressed natural gas (CNG), and ethanol (C₂H₅OH)-fueled internal combustion engine (ICE) automobiles. Port and direct injection and spark and compression ignition engines are examined. We investigate diesel fuel from both petroleum and biosources as well as C₂H₅OH from corn, herbaceous bio-mass, and woody biomass. The baseline vehicle is a gasoline-fueled 1998 Ford Taurus. We optimize the other fuel/powertrain combinations for each specific fuel as a part of making the vehicles comparable to the baseline in terms of range, emissions level, and vehicle lifetime. Life-cycle calculations are done using the economic input-output life-cycle analysis (EIO-LCA) software; fuel cycles and vehicle end-of-life stages are based on published model results.

We find that recent advances in gasoline vehicles, the low petroleum price, and the extensive gasoline infrastructure make it difficult for any alternative fuel to become commercially viable. The most attractive alternative fuel is compressed natural gas because it is less expensive than gasoline, has lower regulated pollutant and toxics emissions, produces less greenhouse gas (GHG) emissions, and is available in North America in large quantities. However, the bulk and weight of gas storage cylinders required for the vehicle to attain a range comparable to that of gasoline vehicles necessitates a redesign of the engine and chassis. Additional natural gas transportation and distribution infrastructure is required for large-scale use of natural gas for transportation. Diesel engines are extremely attractive in terms of energy efficiency, but expert judgment is divided on whether these engines will be able to meet strict emissions standards, even with reformulated fuel. The attractiveness of direct injection engines depends on their being able to meet strict emissions standards without losing their greater efficiency. Biofuels offer lower GHG emissions, are sustainable, and reduce the demand for imported fuels. Fuels from food sources, such as biodiesel from soybeans and C₂H₅OH from corn, can be attractive only if the co-products are in high demand and if the fuel production does not diminish the food supply. C₂H₅OH from herbaceous or woody biomass could replace the gasoline burned in the light-duty fleet while supplying electricity as a co-product. While it costs more than gasoline, bioethanol would be attractive if the price of gasoline doubled, if significant reductions in GHG emissions were required, or if fuel economy regulations for gasoline vehicles were tightened.     

Numerical modeling of dry deposition coupled to 22 photochemical reactions

Three Eulerian models for the dry deposition of photochemically reactive species were formulated and evaluated: a K-theory model with independent transport and deposition of each species, a K-theory model coupled with 22 gas-phase reactions, and a second-order flux-budget model coupled with 22 reactions. Operator splitting was used to separately solve the reaction and dispersion terms in the models including photochemistry. In an evaluation of numerical method performance, the Adams–Moulton method with a pseudo-steady-state approximation for the free radicals was found to be consistent with, but more computationally efficient than Gear’s method for the solution of the reaction terms. The sensitivity of profiles of vertical concentration and flux to the Eulerian model formulation varied according to the species’ Damköhler number. Although a K-theory model is adequate for weakly depositing species with Damköhler numbers <10^-3, a second-order flux-budget model is required for species with Damköhler numbers that exceed unity, such as nitrogen oxides, free radicals, and those sensitive to net flux production by chemical reactions. Selection of an appropriate model formulation for the entire system depended on the most reactive species. Simple K-theory models may not accurately predict dry deposition fluxes in the urban surface layer.     

Factors influencing the variability of SO2 concentrations in Istanbul

The correlation between sulfur dioxide (SO2) concentrations measured at the European and Asian sides of Istanbul and meteorological parameters is investigated using principal component analysis (PCA) and multiple regression analysis techniques. Several meteorological parameters are selected to represent the atmospheric conditions during two winter periods: 1993-1994 and 1994-1995. Six principal components are found to explain the majority of the observed meteorological variability. Surface pressure, 850-mb temperature, and surface zonal (east-west) and meridional (north-south) winds show high loadings on separate factors identified by PCA. We seek dominant meteorological parameters that control the SO2 levels at each monitoring station. Several multiple regression analysis models are fitted to the data from each monitoring station using six principal components and previous-day SO2 concentrations as independent variables. Results suggest that the most important parameters, highly correlated with SO2 concentrations in the Istanbul metropolitan area, are atmospheric pressure and surface zonal and meridional winds. These components have more influence on the determination of the air pollution levels at the Asian side than at the European side.