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Many urban areas in the Eastern United States have been classified to be in non-attainment for ozone, placing a high priority on finding cost-effective emission control measures for improving ambient ozone air quality. Recognizing the complexities associated with the nation’s ozone non-attainment problem, the 1990 Clean Air Amendments mandated the use of grid-based photochemical models for evaluating emission control strategies in urban areas having a serious or higher designation. Given the influx of elevated concentrations of ozone and its precursors into the urban-scale modeling domains (regional-scale transport), many states in the Eastern U.S. were unable to demonstrate ozone attainment for urban areas in their 1994 State Implementation Plans (SIPs) submittal using the urban-scale models. The 1994 SIPs were based on the UAM-IV photochemical model (Morris et al., 1990), which is an urban-scale model that reflects the state-of-science of the late 1980’s. Systems Applications International (SAI) recently developed the UAM-V, a regional-scale ozone air quality model, which contains some new features over the UAM-IV such as multi-scale modeling capability, grid nesting, plume-in-grid (PiG) treatment for point sources, etc. (SAI, 1995). Of particular interest is this model’s treatment of subgrid-scale processes relating to the transport, transformation, and interaction of elevated plumes with the ground-level plume.

The air pollutant transport and transformation processes and especially the photochemically driven ones consist a very complicated problem due to the numerous related factors such as the spatial and temporal distribution of the emissions, the air pollutant transportation and removal mechanisms. Photochemical air pollution is a regional scale problem as this will be argued. In the frame of this presentation the role of the meteorological conditions, the landscape variations and the distribution of emissions in controlling the photochemical pollution are emphasised.

The Mediterranean Sea is closed from all sides and has approximately an elliptical shape. Its major axis of about 3600 km has a W-E orientation, while the N-S width is variable from 200–800 km. It is surrounded by high peninsulas and important mountain barriers. The most important are the Alps and the Balcan Peninsula to the N, the Iberian Peninsula to the W, the Atlas Mountains to the SW, and the Asia Minor to the NE. The Asia Minor Plateau separates the Mediterranean from the Black Sea. The gaps between these major mountainous regions act as channels for the air mass transport from/to the Mediterranean. This kind of transport is considered as very important for the air quality in the Mediterranean Region. These topographic features along with the significant variation of the physiographic characteristics are partially responsible for the development of various-scale atmospheric circulations. These locally produced atmospheric circulations are quite strong, especially during the warm period of the year. The most significant from these regional to mesoscale circulations in the area are described in the publication of the UK. Meteorological Office “Weather in The Mediterranean”, (1962).

It is long been recognized that land and sea contrasts produce sea breezes. More recently, it has become evident that landscape variations which result in spatial gradients in surface heat flux can produce mesoscale circulations as strong as sea breezes. However, it remains to determine how small a horizontal variation in surface heating can still produce a significant mesoscale circulation. It order to address this question, in this paper we present results for one Fourier component. While only the linear response can be evaluated using this tool, such models have been shown to be effective at identifying dominant physical processes associated with sea breezes (Rotunno, 1983; Dalu and Pielke, 1989, 93). This approach can also be used to assist in the development of a parameterization of mesoscale effects generated by spatial surface sensible heat variability for use in larger scale models. The primitive equations can be reduced to an equation for the streamfunction: $$\left[ {{{\left({\frac{\partial }{{\partial x}} + {k_p}} \right)}^2} + k_o^2} \right]\frac{{{\partial ^2}\varphi }}{{\partial {z^2}}} + \left[ {{{\left( {\frac{\partial }{{\partial x}} + {k_p}} \right)}^2} + {l^2}} \right]\frac{{{\partial ^2}\varphi }}{{\partial {x^2}}} = - \frac{1}{{{U^2}}}\frac{{\partial Q}}{{\partial x}}$$ (1) $$\begin{gathered}\frac{{\partial \varphi }}{{\partial z}} = u {\text{and}} \frac{{\partial \varphi }}{{\partial x}} = - w; {l^2} = \frac{{N_o^2}}{{{U^2}}} - \frac{{{U_{zz}}}}{U}; p = s + \lambda ; {k_p} = \frac{p}{U} + \frac{{K{k^2}}}{U} {\text{and}} {k_o} = \frac{f}{U} \hfill \\h = {h_o}\frac{1}{2}\left[ {1 + {a_1}\sin \left( {kx} \right) + {a_2}\cos \left( {kx} \right)} \right] = {h_o}\frac{1}{2}\left[ {1 + a\sin \left( {kx + b} \right)} \right] \hfill \\\end{gathered}$$ (2) $${a_1} = \frac{{\lambda \left( {\lambda + K{k^2}} \right)}}{{{{\left( {\lambda + K{k^2}} \right)}^2} + {k^2}{U^2}}}; {a_2} = - \frac{{\lambda kU}}{{{{\left( {\lambda + K{k^2}} \right)}^2} + {k^2}{U^2}}}; \mathop {\lim }\limits_{k,U \to \infty } {a_1},{a_2} = 0$$ (3) $${h_a} = \frac{1}{2}{h_o}\left( {1 + a} \right) Q = \frac{{{Q_o}q\left( s \right)}}{2}\left[ {1 + a\sin \left( {kx + b} \right)} \right]He\left( {{h_a} - z} \right)$$ (4)

The role of the various-scale circulations (synoptic, regional, sub-regional, mesoscale, microscale) in the dispersion of air pollutants, released from different type of sources, is considered as very important because the 3-D meteorological and turbulence fields show significant temporal variations (e.g. Pielke et al., 1983; Glendening et al., 1986; Segal et al., 1988; Ulrickson and Mass, 1990; Kallos, 1990 among others). This is especially true in areas with significant physiographic variations. Today, allot of mesoscale models are able to provide meteorological and turbulence fields adequate for use in dispersion and/or transformation models (Pielke, 1988; Seigneur, 1989). The combined use of such models is considered as superior from the existing regulatory models because they should provide a more realistic description of the dispersion characteristics and the spatial and temporal variations of the concentration fields of air pollutants on more accurate manner. Despite this fact, the use of such models may lead in erroneous calculations for several reasons. The most important reasons are the mishandling from the models the physical processes taking place under certain circumstances and of course the improper use of them. The improper use may be due to the violations of physical rules which are not necessarily associated with the algorithms and the chosen initial and boundary conditions.

In this work, the climatological data (surface and upper-air) collected in the Greater Athens Area (GAA) for the period 1974–1990 was analysed. Based on this data and the air quality data collected for the period 1983–1990, the air pollution episodes were analysed and classified. The synoptic conditions during the episodes were classified too. It was found that the worst pollution episodes in Athens occur during days with critical balance between synoptic and mesoscale circulations. During these days, stagnant atmospheric conditions occur in the area. For two representative cases, model simulations were performed with mesoscale and regional atmospheric models. Model results compare quite well with observations. With these simulations, some critical points which must be taken into account in air pollution studies in the area of Athens were pointed out. Dispersion calculations in the area are under way.

The Sahara desert is one of the major sources of mineral dust on Earth, producing up to 2x108 t yr-1. A combined effort has been devoted during the last ten years at the University of Athens (UOA) from the Atmospheric Modeling and Weather Forecasting Group (AM&WFG) to the development of an analysis and forecasting tool that will provide early warning of Saharan dust outbreaks. The developed tool is the SKIRON limited-area forecasting system, based on the Eta limited area modeling system with embedded algorithms describing the dust cycle. A new version of the model is currently available, with extra features like eight-size particle bins, radiative transfer corrections, new dust source identification and utilization of rocky soil characterization and incorporation of more accurate deposition schemes. The new version of SKIRON modeling system is coupled with the photochemical model CAMx in order to study processes like the shading effect of dust particles on photochemical processes and the production of second and third generation of aerosols. Moreover, another new development in the AM&WFG is based on the RAMS model, with the incorporation of processes like dust and sea-salt production, gas and aqueous phase chemistry and particle formation. In this study, the major characteristics of the developed (and under development) modeling systems are presented, as well as the spatiotemporal distribution of the transported dust amounts, the interaction with anthropogenically-produced particles and the potential implications on radiative transfer.

In order to accurately evaluate environmental impacts from the operation of industrial installations it is necessary to identify some crucial atmospheric parameters such as the development of the Planetary Boundary Layer (PBL) and the 3-D wind field. This is especially true in complex coastal areas where a variety of phenomena including sea-land breezes, convergence zones, drainage flows from surrounding topography, and the development of thermal internal boundary layers make the dispersion processes very complicated (Hanna, 1987; McKendry, 1989). In almost all cases where standard dispersion modelling approaches are applied, some over-simplifications are made for the PBL depth and the wind fields. Such over-simplifications are the spatial homogeneity of the PBL depth and its simple diurnal variation which is usually approximated from indirect methods based on observations and empirical formulation. However, previous studies (Pielke et al., 1983; Glendering et al, 1986; Segal et al., 1988; McKendry, 1989) suggest that large spatial and temporal variations in PBL depth may occur over coastal regions when marine air is advected over land. Of course, significant variations in to the wind field are observed at the same time. These variations are more significant when the marine air incursion occurs over irregular terrain with significant topographic variations. In such cases, even if a dense observational network is available, it is almost impossible to accurately resolve the detailed spatial and temporal variations in both the wind field and PBL depth, parameters considered crucial for detailed air quality investigations. One good approach for such investigations is the use of a mesoscale numerical model capable to accurately describe the PBL depth and wind fields. In addition, with the use of a Lagrangian type dispersion — diffusion model it is possible to investigate the environmental impacts from industrial activities.

Prevention is one of the most important stages in wildfire and other natural hazard management regimes. Fire danger rating systems have been adopted by many developed countries dealing with wildfire prevention and pre-suppression planning, so that civil protection agencies are able to define areas with high probabilities of fire ignition and resort to necessary actions. This present paper presents a fire ignition risk scheme, developed in the study area of Lesvos Island, Greece, that can be an integral component of a quantitative Fire Danger Rating System. The proposed methodology estimates the geo-spatial fire risk regardless of fire causes or expected burned area, and it has the ability of forecasting based on meteorological data. The main output of the proposed scheme is the Fire Ignition Index, which is based on three other indices: Fire Weather Index, Fire Hazard Index, and Fire Risk Index. These indices are not just a relative probability for fire occurrence, but a rather quantitative assessment of fire danger in a systematic way. Remote sensing data from the high-resolution QuickBird and the Landsat ETM satellite sensors were utilised in order to provide part of the input parameters to the scheme, while Remote Automatic Weather Stations and the SKIRON/Eta weather forecasting system provided real-time and forecasted meteorological data, respectively. Geographic Information Systems were used for management and spatial analyses of the input parameters. The relationship between wildfire occurrence and the input parameters was investigated by neural networks whose training was based on historical data.

[1] Presented herein is an analysis of an exceptionally intensive central and eastern Mediterranean dust intrusion of 15–16 March, 1998. The intrusion has been associated with development of an intense cyclone over Africa. The weather and dust development processes were simulated with the Eta weather and dust prediction model. Also presented is a comparison of the model results with the Total Ozone Mass Spectrometer Aerosol Index (TOMS AI) pictures as well as with those of the surface and weather observations. The roles of the main processes responsible for the dust plume development and associated dust intrusion to the eastern Mediterranean (EM) are studied. The observation data as well as the model-simulated parameters are jointly analyzed. The analysis also includes the data from the back-trajectory computations. With the aid of the model-produced dust profiles we studied the significant variation in the altitudes of the dust layers within the cyclone sectors. In the warm sector of the cyclone located over the Mediterranean Sea the dust layer extended up to 8–10 km. Relatively low dust concentration values were found here. In the area of the cold front over Africa the dust was restricted to the lower troposphere and the planetary boundary layer. Here the model simulated high values of the dust concentrations. The sharp TOMS AI increase over Israel and the eastern Mediterranean up to 5.0 units, further away from the dust sources, is explained by the strong winds, by the increased cyclone convergence, and the formation of a two-layer dust plume.

[1] The detection of high ozone levels over large inland areas in Israel during the early, mid and late summer triggered an analysis of air mass back-trajectories. This, in turn, pointed to the transportation system in the metropolitan coastal Tel Aviv region as the possible origin of the ozone’s precursors. To link the daily dynamics of rush hour transportation emissions to inland air pollution, in general, and airborne ozone measurements, in particular, an interdisciplinary modeling system was established. The simulations of transportation-to-inland air pollution integrated transportation, emission factor, atmospheric, transport/diffusion, and photochemical models. The modeling results elucidated a spatial and temporal overlap between the ozone precursors and ozone production. The model simulations indicated east to southeasterly dispersion of the pollution cloud. The results agreed well with both spatial and temporal ozone levels as recorded by aircraft over central Israel, as well as with ground-based monitoring station observations. The impact of the Tel Aviv metropolitan area as well as the Gaza Strip, as pivotal coastal transportation sources for inland air pollution in general and ozone formation in particular, is discussed. The synoptic analysis identified the conditions prevailing when elevated air pollution, and especially high ozone levels, exists over central Israel. The analysis showed that this season features a shallow mixed layer and weak zonal flow, which leads to poor ventilation rates and inhibit efficient dispersion of this secondary pollutant. These poor ventilation rates result in the slow transport of ozone precursors, enabling their photochemical transformation under intense solar radiation during their travel from the coast inland. Under these conditions, model results showed that traffic emissions during the morning rush hour from the Tel Aviv metropolitan area contribute about 60% to the observed ozone concentrations. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); KEYWORDS: air pollution, numerical atmospheric modeling, transportation model, emission factors, photochemical model, ozone, photochemical aged air mass

In this study, an extreme ozone episode that occurred during the period 12-15 July 1995 over the north-eastern United States is investigated through model simulations. This paper is focused on the meteorological conditions prevailing during this ozone episode. The analysis is based on nested grid simulations performed with the meteorological model CSU-RAMS (Colorado State University - Regional Atmospheric Modelling System) and on the available surface and upper air observations. The definition of the model nests seemed very important in order to capture the prevailing atmospheric circulations which led to the build up of the air pollution episode.

In this study, an attempt was made to investigate the influence of the lateral boundaries and the background concentrations on the predicted air pollutants' concentrations, as calculated by limited area, grid-based photochemical models. This influence is more pronounced in the case of mesoscale applications because of the limited domain. The lateral boundaries should be defined in such a way as to take into account the recirculation phenomena that occur as a result of the interaction of different scale atmospheric circulations. In addition, the influence of air pollutant sources located near the domain boundaries (inside or outside), on the concentrations of the photochemical pollutants inside the domain have to be considered. In this study, the UAM-IV photochemical model has been implemented and simulations have been performed over the Athens Basin. It was found that the concentrations of the photochemical oxidants are mainly affected by the lateral boundary conditions, while the influence of the background is evident in the first hours of the simulation.

The impact of very wet soil and canopy temperatures on the surface sensible heat flux, and on related daytime boundary-layer properties is evaluated. For very wet soils, two winter situations are considered, related to significant changes in soil surface temperature: (1) due to weather perturbations at a given location, and (2) due to the climatological north–south temperature gradient. Analyses and scaling of the various boundary-layer properties, and soil surface fluxes affecting the sensible beat flux, have been made; related evaluations show that changes in the sensible heat flux at a given location by a factor of 2 to 3 due to temperature changes related to weather perturbations is not uncommon. These changes result in significant alterations in the boundary-layer depth; in the atmospheric boundary-layer warming; and in the break-up time of the nocturnal surface temperature inversion. Investigation of the impact of the winter latitudinal temperature gradient on the above characteristics indi...

Proper design and performance prediction of solar energy systems requires accurate information on the availability of solar radiation. However, the complexity and cost of a reliable radiation measuring network dictates the need for developing alternatives that can replace and/or complement observations. Dependable solar radiation models are an alternative. In this paper, two years of solar radiation data from the National Observatory of Athens, Greece (37.5°N, 23.5°E, 107 m above MSL) are used to develop a continuous piecewise linear regression model that predicts hourly direct irradiation values when only global irradiation data are available. The applicability of the Randall-Whitson [7] and Jeter-Balaras [9] models in the area of Athens is also evaluated. For the urban atmospheric conditions of Athens the developed two year correlation provides a better fit to the empirical data.

The present study provides a preliminary evaluation of mesoscale circulations forced by surface gradients of heating arising from irrigated areas adjacent to dry land, utilizing a combination of satellite, observational, and modeling approaches. The irrigated crop areas of northeast Colorado were chosen for the study. For the cases studied satellite surface infrared temperature data indicated a typical temperature contrast of approximately 10 K at noon, between the irrigated area and the adjacent dry land. Surface observations and aircraft measurements within the lower region of the atmospheric boundary layer indicated, in general, a significant temperature contrast and moisture difference, thereby implying a potential thermally driven circulation. The anticipated thermally induced flows, however, were reflected in the measurements only by modest changes in the wind speed and wind direction across the contrast location. It is suggested that the daytime, elevated, terrain-forced flow in the area, ...

Observations of a severe form of rainband, which is comprised of a line of strong but shallow convection, suggest that the environment into which it moves is nearly neutrally stratified with respect to moist convection. A simple two-dimensional model of a severe rainband has been developed to explore how the cold air at the base of the rainband modifies local stability as it underruns the saturated surface layer. This dynamic lifting is found to have two distinct effects. First, the lifted fluid contains regions of absolute and conditional instability. Then it also reorganizes the midtroposphere into a sequence of elevated inversions set between unstable layers. This latter effect results from the intense “lee wave” response in the air flow. The elevated inversions would appear to cap the severe moist convection, establishing the rainband character rather than allowing the deep cellular convection of squall lines. The flow disturbances end abruptly at the steering level (a critical level for the ...

In this paper, an analysis of the meteorological parameters that affect SO2 pollution in Athens, a problem of both local and international concern, is presented. The influence of these meteorological parameters on the SO2 concentrations has been investigated by a statistical analysis of the daily average SO2 values measured at six locations in the Athens basin for the six years from 1974 to 1979. Wind speed, minimum temperature and amount of rain has been found to control SO2 concentrations during the cold season while wind speed, wind direction and relative humidity are central in the warm season. Based on this, multiple regression models, both linear and non-linear, for the prediction of the next day's SO2 concentration have been derived that explain more than 50% of the data variance. Further improvements on the modelling are contingent on the availability of boundary layer structure data and on details of the local wind field. The meteorology of high concentration episodes has also been examined and the synoptic characteristics for the onset and end of such episodes have been identified. Finally, discriminant analysis classification functions, utilizing forecast meteorological variables have been obtained which are capable of predicting accurately the occurrence of high pollution concentrations.

For a propagating mesoscale system whose intensity and structure is not changing with time, relatively coarse horizontal profiler resolution is sufficient to resolve the feature since the circulation would pass by the profiler sites quickly enough to construct a three-dimensional analysis. This is generally not true for a thermally forced mesoscale system. For mesoscale systems generated by surface inhomogeneities in surface heating (e.g., land-sea contrasts, nonuniform soil wetness, etc.), such propagation is often slow. Therefore, ideally, if thermally surface-forced systems are to be directly resolved by a profiler network, a necessary condition is that their spacing be close enough to adequately resolve the motion field of the mesoscale system. As concluded from the analyses in this paper, higher spatial resolution is required to directly monitor the horizontal wind field than the temperature field, since the horizontal wind is proportional to the horizontal gradient of temperature. Similarly...

The Black Sea is closed from all sides by land and communicates with the Aegean Sea and Mediterranean through the Vosporous strait (Fig. 1). It is surrounded by land with elevation varying from a few meters to a few kilometers. The most important orographic features are located at the eastern and south-eastern sides. More specifically, there is the Caucasus Peninsula in the East and the Pontine Mountains across the northern Turkish coast. Towards west, there is the opening of the Danube Valley with the Carpathian mountains to the North of it and the Balkan Peninsula to the South in a considerable distance from the coast. The northern part is adjacent to almost flat land with relatively complicated coastline. At a larger distance, the Balkan and Asia Minor Peninsulas together with the Aegean Sea between them and the Mediterranean Region in general are forming a unique pattern for the development of atmospheric circulations of a wide spectrum ranging from the synoptic to meso-gamma scale with significant implications to the air quality of the region.

In this study, an attempt was made to analyze time series of air quality measurements (O3, SO2, SO4(2-), NOx) conducted at a remote place in the eastern Mediterranean (Finokalia at Crete Island in 1999) to obtain concrete information on potential contributions from emission sources. For the definition of a source-receptor relationship, advanced meteorological and dispersion models appropriate to identify "areas of influence" have been used. The model tools used are the Regional Atmospheric Modeling System and the Lagrangian-type particle dispersion model (forward and backward in time), with capabilities to derive influence functions and definition of "areas of influence." When high levels of pollutants have been measured at the remote location of Finokalia, particles are released from this location (receptor) and traced backward in time. The influence function derived from particle distributions characterizes dispersion conditions in the atmosphere and also provides information on potential contributions from emission sources within the modeling domain to this high concentration. As was shown in the simulation results, the experimental site of Finokalia in Crete is influenced during the selected case studies, primarily by pollutants emitted from the urban conglomerate of Athens. Secondarily, it is influenced by polluted air masses arriving from Italy and/or the Black Sea Region. For some specific cases, air pollutants monitored at Finokalia were possibly related to war activities in the West Balkan Region (Kosovo).