Numerical simulation of the photochemical air pollution levels in Athens,Greece

This paper focuses on photochemical oxidant formation which is shown to be the most dominant feature of the Athenian air pollution problem. A simple but reliable photosmog model is used to simulate numerically the formation of photochemical oxidants on the basis of all available emission data. The resulting diurnal variation of the ozone concentration agrees fairly well with measurements. Predictions of the future development of the photosmog levels performed on the basis of realistic emission forecasts allow to conclude that no significant reduction of the photochemical air pollution in Athens can be expected in the next 25 years.     

Atmospheric boundary layer field measurements over coastal areas

This paper reviews the main field campaigns and their results, performed within the Greater Athens Area (GAA) during the last years in order to examine closely the emission and transport mechanisms in the Athens basin. In this respect the flows and the different circulation patterns of the wind combined with the dispersion of different pollutants emitted from various points, area or line sources, were studied. Various parameters such as the topographical effects, or local circulation patterns were examined in order to establish their contribution to the pollution levels in the different areas of the Athens basin.     

Improved parameterisation for the numerical modelling of air pollution within an urban street canyon

Numerical modelling for application to wind flow and dispersion in urban environments has noticeably progressed in recent years, to currently represent a widely used tool for simulating mechanical processes governing air pollution in complex geometries. In particular, Computational Fluid Dynamic (CFD) techniques based on RANS (Reynolds-Averaged Navier–Stokes equations) models, are extensively used to produce detailed simulations of the wind flow and turbulence in the urban canopy. However, several studies have indicated that RANS models, and in particular the widely used standard k–? turbulence model, are sensitive to the particular form of inlet profiles for turbulence and velocity. In the present study, simulations of the wind flow and dispersion within an idealised street canyon were carried out using the standard k–? turbulence model provided by the commercial software FLUENT. The aim of this study was to improve the standard k–? model performance by modifying the model parameters according to the chosen form of inlet profiles for velocity and turbulence. Capability of the model to reproduce real wind flow fields, turbulence and concentration patterns was evaluated by comparing the model results against recently published wind tunnel data. Results for turbulent kinetic energy and concentration showed that the redefinition of the default dispersive parameters can significantly enhance the model performance. The newly proposed parameterisations of the standard k–? turbulence model can be readily implemented within commercial CFD software packages, offering a reliable modelling tool for application to urban air pollution and other environmental studies.     

Short-term air quality prediction using a case-based classifier

In the frame of air quality monitoring of urban areas the task of short-term prediction of key-pollutants concentrations is a daily activity of major importance. Automation of this process is desirable but development of reliable predictive models with good performance to support this task in operational basis presents many difficulties. In this paper we present and discuss the NEMO prototype that has been built in order to support short-term prediction of NO₂ maximum concentration levels in Athens, Greece. NEMO is based on a case-based reasoning approach combining heuristic and statistical techniques. The process of development of the system, its architecture and its performance, are described in this paper. NEMO performance is compared with that of a back propagating neural network and a decision tree. The overall performance of NEMO makes it a good candidate to support air pollution experts in operational conditions.     

Collaborative virtual geographic environments: A case study of air pollution simulation

The integration of high dimensional geo-visualization, geo-data management, geo-process modeling and computation, geospatial analysis, and geo-collaboration is a trend in GIScience. The technical platform that matches the trend forms a new framework unlike that of GIS and is conceptualized in this paper as a collaborative virtual geographic environment (CVGE). This paper focuses on two key issues. One is scientific research on CVGE including the concept definition and the conceptual and system framework development. The other is a prototype system development according to CVGE frameworks for air pollution simulation in the Pearl River Delta. The prototype system integrates air pollution source data, air pollution dispersion models, air pollution distribution/dispersion visualization in geographically referenced environments, geospatial analysis, and geo-collaboration. Using the prototype system, participants from geographically distributed locations can join in the shared virtual geographic environment to conduct collaborative simulation of air pollution dispersion. The collaborations supporting this simulation happen on air pollution source editing, air pollution dispersion modeling, geo-visualization of the output of the modeling, and geo-analysis.     

Modelling chain for the effect of road traffic on air and water quality: Techniques,current status and future prospects

Modelling approaches for simulating air and stormwater pollution due to on-road vehicles are reviewed and discussed. Models for traffic, emissions, atmospheric dispersion, and stormwater contamination are studied with particular emphasis on their couplings to create a modelling chain. The models must be carefully selected according to the requirements and level of detail of the integrated modelling chain. Although a fair amount of research has been conducted to link air pollution and road traffic, many questions related to spatio-temporal scales, domains of validity, consistency among models, uncertainties of model simulation results, and interfaces between models remain open. The aim of this work is to review the current status of the relationships between traffic, emissions, air quality, and water quality models, to recommend modelling approaches and to propose some directions for improving the state of the science. The difficulties and challenges associated with model coupling are illustrated with specific examples.     

Patterns of SO2 emissions: a refinery case study

Air quality modelling is an essential tool for most air pollution studies and the introduction of SO₂ standards creates a need for modelling the dispersion of SO₂. This work deals specifically with the use of the Industrial Source Complex Short Term (ISCST) model at a refinery. The study is performed over a period of 21 days. The first objective of this study was to measure the atmospheric levels of SO₂ and then to compare their values with the international standard limits. The second objective was to evaluate the ISCST model by comparing the calculated and measured concentrations. The third objective was to demonstrate the effect of wind regimes on the dispersion of SO₂ and to determine the spatial distribution of SO₂ over the modelled area. The results showed that the levels of SO₂ were well below the ambient air quality standard. Based on isopleths for SO₂ distribution in the study area (as output from the ISCST model), it can be stated that no health risk is present in areas adjacent to the refinery.     

Efficient sensitivity computations in 3D air quality models

The prediction of ground level ozone for air quality monitoring and assessment is simulated through an integrated system of gridded models (meteorological, photochemical), where the atmosphere is represented with a three-dimensional grid that may include thousands of grid cells. The continuity equation solved by the Photochemical Air Quality Model (PAQM) reproduces the atmospheric processes (dynamical, physical, chemical and radiative), such as moving and mixing air parcels from one grid cell to another, calculating chemical reactions, injecting new emissions. The whole modeling procedure includes several sources of uncertainty, especially in the large data sets that describe the status of the domain (boundary conditions, emissions, chemical reaction rates and several others). The robustness of the photochemical simulation is addressed in this work through the deterministic approach of sensitivity analysis. The automatic differentiation tool ADIFOR is applied on the 3D PAQM CAMx and augments its Fortran 77 code by introducing new lines of code that additionally calculate, in only one run, the gradient of the solution vector with respect to its input parameters. The applicability of the approach is evaluated through a sensitivity study of the modeled concentrations to perturbations at the boundary conditions and the emissions, for three essentially dissimilar European Metropolises of the Auto-Oil II programme (Athens, Milan, and London).     

Large-scale convex optimization methods for air quality policy assessment

This paper presents the implementation of a large-scale systems analytic method in a model permitting the assessment of air quality policies in urban regions. This method is based on the use of a convex optimization technique called the analytic center cutting plane method. One realizes the coupling of a photochemical model (TAPOM-Lite), used to simulate ozone creation and dispersion in the region under study, and of a technoeconomic model (MARKAL-Lite) that represents the technology and energy uses by different economic sectors in the same region. Although the models correspond to different time and space scales, one realizes the coupling through a series of approximating convex reduced order optimization problems with constraints that are implicitly defined by the photochemical and the technoeconomic model, respectively. The implementation of the method in a case study corresponding to the region of Geneva, Switzerland is described.     

CASE-BASED REASONING IN ENVIRONMENTAL MONITORING APPLICATIONS

Environmental monitoring is usually based on large volumes of data, while in general, environmental decision making is a complex problem, has a high degree of uncertainty, and involves diverse areas of expertise. Environmental decision-support systems are therefore good candidates for application of artificial intelligence (AI) techniques. In this paper it is argued that a suitable approach for building these systems is the use of case-based reasoning or analogical reasoning techniques, which offer more adaptability and better explanation facilities than other AI paradigms. As an example, the development stages, the architecture, and the operational characteristics of the expert system Air Quality Predictor (AIRQUAP), developed to predict air pollution levels in Athens, Greece, are described. AIRQUAP helps users retrieve historical data intelligently and can predict air pollution levels, useful for management of air pollution episodes. The performance of the system is also compared with other techniques used in this class of applications.     

A computationally efficient particle-puff model for concentration variance from steady releases

This paper presents a computationally efficient particle-puff model that can be used to calculate both average concentration and concentration variance in turbulent flows. The model is self-contained in the sense that it does not need externally supplied parameterizations of puff spread, but rather calculates the spread with an internally-built module for relative dispersion of particles—all existing particle-puff models rely on parameterizations of puff spread derived from theoretical considerations and observational data for dispersion of a point source in isotropic turbulence.Preliminary evaluations show that the model performs as well as a computationally demanding two-particle trajectory model in predicting the mean concentration and concentration variance in two different flows: isotropic turbulence and a wind tunnel boundary layer. Because of its numerical efficiency, the present particle-puff model can be built into conventional, regulatory air quality models as a module to calculate the mean concentration and concentration variance in the near field.The reason for the numerical efficiency of present particle-puff model is that it needs to track only thousands of particle-pairs in order to calculate the puff spread, while (the original) two-particle Lagrangian stochastic (LS) models need millions of particle-pairs to achieve statistically stable predictions.     

An efficient chemical systems modelling approach

Systems of stiff chemical reactions are often associated with atmospheric chemistry modelling, which plays a very important role in the studies of stratospheric ozone depletion, tropospheric air pollution problems, and future chemistry-climate feedbacks and interactions. This paper revisits an open-source stiff system solver SVODE and presents its efficient use in modelling different levels of complexity of a range of chemical systems. The chemical systems discussed here are the Lotka–Volterra (predator–prey) model, the Brusselator model, the Oregonator model, and the Lorenz model. The first two models consist of two variables, while the remaining two models consist of three variables. Finally, an application of this modelling approach to a generalised organic/NOx mechanism for characterising air pollution development is presented. Since the SVODE is an open-source code, and the simulations were run on a Linux PC (with g77 compiler), all results discussed in this paper can be easily reproduced. Most importantly, the approach shown here can be readily extended to other larger scale applications such as the three-dimensional air pollution modelling.     

Real-time urban power dispatch with ambient air quality constraints

A power dispatch methodology for urban utility company facing ambient air quality constraints is developed. This approach consists of (1) a real-time air dispersion model for the urban area and its surrounding region, (2) a fuel minimization procedure which will generate a schedule to satisfy the demand and the constraints on pollution concentration. Forecast meteorological data and ambient air quality information are assumed available for the procedure.     

Evidence of sea-breeze flow at the top of Hymettos mountain

Results from an observational study of a sea-breeze flow at the top of a steep mountain are presented and discussed. Measurements of the profiles of temperature, humidity, wind speed and direction from a tethered balloon are given together with the hourly variations of the same parameters at surface level, The thermal structure of the atmospheric boundary layer (ABL) along with the profiles of the temperature structure parameter (C² _T) and the vertical wind component variance (σ² _w) obtained by acoustic sounder at the mountain top are also included.

An attentive examination of the collected data indicates the presence of sea-breeze flows on top of the 1000?m height mountain. This is of importance, especially in cases like Athens, where the understanding of the wind flow is necessary for the study of the air pollution problem     

Easy to use air pollution model for turbulent shear flow

A three-dimensional model for air pollutant dispersion, based on an analytical solution of the advection-diffusion equation, is presented. Vertical and along wind dispersion is described by an analytic solution valid for power law profiles of wind and eddy exchange coefficient while a Gaussian formula describes the lateral one. The model is implemented in GW BASIC MS-DOS for the microcomputer RAINBOW 100 PLUS DIGITAL in interactive mode. The program, easy to use, is listed and an example of the output is given.     

Further evidence of the role of air pollution on solar ultraviolet radiation reaching the ground

The influence of photochemical pollution on the ultraviolet radiation reaching the ground is examined. For this purpose, a series of UV-A and UV-B measurements as well as the results of a simple parametric model are compared. It was found that the hypothesis of UV-B depletion is significant at an almost 95 per cent confidence level. It is also indicated that the effect of photochemical pollution on UV-B levels reaching the ground is roughly three times the same effect on UV-A levels.     

空间决策支持系统的集成体系结构及其实现途径

文章以厦门市环境管理空间决策支持系统为例,提出一个以地理信息系统为中心的环境空间决策支持系统的体系结构新类型,在此基础上构造了基于集成方式实现的环境空间决策支持系统的逻辑结构,并介绍了实现GIS与空间应用分析模型嵌入式紧密集成的具体实现方法和应用例子。     

Computer simulation of air pollution chemistry

The computer simulation of air pollution chemistry is a powerful technique for the understanding of the formation of air pollutants and the development of effective strategies for the control of air pollution. The present status of computerized mathematical modeling of air pollution chemistry is reviewed, typical examples of recent applications are presented and present areas of uncertainties are discussed. The four major areas of air pollution chemistry that are reviewed include photochemical oxidants, acid deposition, atmospheric aerosols and air toxics. The effect of atmospheric physical processes on air pollution chemistry if briefly discussed. The numerical techniques used for the simulation of atmospheric chemistry are reviewed.     

The EOLE Project: A multiwavelength laser remote sensing (lidar) system for ozone and aerosol measurements in the troposphere and the lower stratosphere. Part II: Aerosol measurements over Athens,Greece

Ground-based measurements of suspended aerosols in the lower troposphere (0.6-3.5 km height) in Athens, Greece were performed for a period of 10 days in November 1994. The measurements were performed in a suburban area in the northern part of the Athenian basin, using a two-wavelength backscattering lidar system operating at 355 nm and 532 nm, simultaneously. The lidar system was pointing vertically and was operated under different meteorological conditions. A lidar inversion algorithm was applied to determine the vertical profile of the aerosol backscattering coefficient in the 0.6-3.5 km altitude range. The analysis of the bi-dimensional cross-section of the aerosol backscattering coefficient and slope rate, for two selected cases, in conjunction with radiosonde, solar UV-B irradiance and in situ air pollution data, gave the possibility to study air pollution characteristics inside the Athens basin.