Dimitrios Melas

Forecasting peak pollutant levels from meteorological variables

The main objective of this paper is to present analytical models relating maximum pollutant concentrations in urban areas with meteorological and other variables. The analysis is based on measurements from Greater Athens Area and is restricted in only one pollutant of special interest, namely N02. The meteorological variables, used in analytical modeling for forecasting pollution concentrations, cover the most important atmospheric processes favoring pollution episodes. The selection of the variables was based both on extensive correlation analysis and on the existing knowledge from the scientific literature. The evaluation of the developed forecasting models showed that their degree of success is promising. The final model equations derived are simple and they can be used easily for operational forecasts from the air quality management authorities.

The depth of the internal boundary layer over an urban area under sea-breeze conditions

Field data are analyzed in order to study the development of the Thermal Internal Boundary Layer (TIBL) under sea breeze conditions. The measurements were carried out by the National Observatory of Athens (NOA) during ATHens Internal Boundary Layer Experiment (ATHIBLEX) in summer 1989 and 1990.Several formulations found in the literature are tested against the measurements in order to investigate whether they are capable of predicting the depth of the TIBL. It is found that a slab model including mechanical production of turbulence gives overall good agreement with the measurements.Finally, the concept of local equilibrium is used to explain the discrepancies found between small-and meso-scale observations and models; a formula is proposed which is intended for use over a wide range of downwind fetches.

Air quality in the Athens basin during sea breeze and non-sea breeze days using laser-remote-sensing technique

It is well established both from theory and experimental evidence that sea breeze plays an advert role on air pollution situation over a coastal urban area, specially during summer. This also applies to Athens area. Ground-based measurements in the area have shown that northerly wind flows during summertime play a depollution role in the Greater Athens Area. A wind field over a city is responsible for a mechanism forming a particular profile of the air pollutant considered; such air pollutant profiles were found in Athens for first time to a height of 1200 m in the Atmospheric Boundary Layer during an experimental campaign in the summer of 1994. The paper gives profiles of ozone and nitrogen dioxide on sea-breeze and non-sea-breeze days with possible explanations. Air quality aspects within the first 1500 m of the Atmospheric Boundary Layer over Athens are also discussed.

Boundary layer dynamics in an urban coastal environment under sea breeze conditions

Abstract A three-dimensional, higher-order turbulence closure model is applied to simulate the boundary layer dynamics in Attica peninsula, where the city of Athens is located. All model equations are transformed to a terrain influenced coordinate system, which enables studies of flow over complex terrain. Major characteristics of the sea breeze circulation including vertical extension and intensity as well as the growth rate of the thermal internal boundary layer are identified and discussed. Model predictions agree fairly well with measured profiles at one location and measured surface winds in the center of Athens. In addition to the basic simulations, a series of sensitivity tests has been performed in order to evaluate the relative importance of the various input parameters. It was found that some parameters (topography, the amplitude; of the diurnal variation of the temperature over the land) have relatively larger impact on the development of sea breeze circulation over the Athens basin than others. The sea breeze circulation developing at the east side of the Attica peninsula is particularly sensitive to the input geostrophic wind.

Anatomy of the sea-breeze circulation in Athens area under weak large-scale ambient winds

Abstract The city of Athens is located near an irregular coastline and is surrounded by moderately high mountains. The complex structure of the sea breezes developing in Greater Athens Area (GAA) during a day with weak large-scale ambient winds is examined using consolidated field data and results from numerical model simulations. The data used in the analysis are from the MEDditerranean CAmpaign of PHOtochemical Tracers-TRAnsport and Chemical Evolution (MEDCAPHOT-TRACE) which took place in the GAA during the period 20 August–20 September 1994. The numerical simulations were performed using a three-dimensional, higher-order turbulence closure model. All model equations are transformed to a terrain-influenced coordinate system, which enables studies of flow over complex terrain. A full diurnal cycle has been simulated for the typical sea-breeze day of 15 September 1994. Major characteristics of the sea-breeze circulation including surface wind pattern, inland penetration of the sea-breeze front and vertical extension and intensity as well as diurnal variation of the vertical eddy thermal diffusivity are identified and discussed. Model predictions show a good agreement with the comprehensive data set.

A model for European Biogenic Volatile Organic Compound emissions: Software development and first validation

A grid-oriented Biogenic Emission Model (BEM) has been developed to calculate Non-Methane Volatile Organic Compound (NMVOC) emissions from vegetation in high spatial and temporal resolutions. The model allows the emissions calculation for any modeling domain covering Europe on the basis of: 1) the U.S. Geological Survey 1-km resolution land-use database, 2) a land-use specific, monthly isoprene, monoterpene and Other Volatile Organic Compound (OVOC) emission potentials and foliar biomass densities database, 3) temperature and solar radiation data provided by the mesoscale meteorological model MM5. The model was applied for Europe in 30-km spatial resolution for the year 2003. The European total emissions for 2003 consist of 33.0% isoprene, 25.5% monoterpenes and 41.5% OVOC. BEM results are compared with those from the well-documented global Model of Emissions of Gases and Aerosols from Nature (MEGAN). The BEM total emissions compare well with the MEGAN ones. In July 2003, the results of both models agree within a factor of 1.2 for total isoprene emissions and within a factor of 2 for total monoterpene emissions. The comparison of the spatial distributions of the July 2003 isoprene and monoterpene emissions calculated with BEM and MEGAN shows that, in the greater part of the study area, the differences are below the current uncertainty limit for the estimation of spatially-resolved biogenic VOC emissions in Europe being equal to about +/-600 kg km^-^2 month^-^1. Differences that are above this limit are found mainly in the eastern European countries for isoprene and in the Mediterranean countries for monoterpenes.

A GIS based anthropogenic PM10 emission inventory for Greece

An anthropogenic, chemically speciated PM10 emission inventory was compiled for Greece in 10 km spatial resolution. The inventory comprises of all anthropogenic particulate matter sources and it was compiled using a Geographical Information System (GIS) integrated with SQL programming language. Input data from the national and international databases were used for the calculation of spatially and temporally resolved emissions for the road transport and all the subsectors of the other mobile sources and machinery sector using top–down or bottom–up methodologies. Annual data from existing emission databases were also used and were temporally and spatially disaggregated using source relevant statistical data and high resolution maps. The sectoral emission totals are compared with other emission databases or studies conducted in the area. Total anthropogenic emissions in Greece were estimated to be 182 219 t for the base year 2003. The results indicate the industrial sector as the major PM10 emission source (39.9% contribution) with the major industrial units though to be situated inside the organised industrial areas of the country. The power generation sector (21.4%) is the second largest contributor in national level mostly derived from one specific industrial region at north. International cargo shipping activities (9.6%) is also an important source category for particles. Heat production and road transport are found to play a significant role inside the urban centres of the country.

An environmental experiment over Athens urban area under sea breeze conditions

Abstract Instrumental and technical details as well as results from ATHens Internal Boundary Layer EXperiment (ATHIBLEX) are presented in this paper. This experiment was performed during June 1989 and June–July 1990. The aim of ATHIBLEX was to study the IBL formation over Athens urban area under sea breeze conditions and its association with the city environmental problems. The results show a well established IBL over Athens basin. A slab model is adopted to estimate IBL heights at positions where no measurements were taken. The orograhic effect of Athens basin on the wind profiles is also demonstrated. u ′-, v ′- and w ′-power spectral densities from a uvw propeller anemometer installed 4500 m downwind of the shoreline on the top of a hill 107 m a.m.s.l. exhibit the −5/3 law.

An Investigation of the Boundary Layer Dynamics of Sardinia Island under Sea-Breeze Conditions

A numerical mesoscale model is used to study the wind field and the boundary layer structure of the island of Sardinia during typical summer conditions. The numerical model is three-dimensional and employs a higherorder turbulence closure scheme. The model simulations were performed for summer conditions characterized by weak synoptic forcing from the northwest and clear skies. These conditions favor the development of thermal circulations, the most significant of which are the sea-breeze systems. The nighttime wind patterns generally are dominated by topography, which leads to the development of strong drainage flow. On the other hand, as revealed in the simulated wind field, at midday the wind has an onshore component at virtually every coastline. The well-organized sea-breeze systems interact to produce convergence zones. Another interesting feature is the development of a cyclonic eddy pattern during late-afternoon hours. The model results are compared with observations taken at a network of near-surface wind stations and rawinsonde profiles from the Cagliari airport. Available observations agreed relatively well with model predictions.

Neural network model for predicting peak photochemical pollutant levels

ABSTRACT In this paper, an attempt is made for the 24-hr prediction of photochemical pollutant levels using a neural network model. For this purpose, a model is developed that relates peak pollutant concentrations to meteorological and emission variables and indexes. The analysis is based on measurements of O3 and NO2 from the city of Athens. The meteorological variables are selected to cover atmospheric processes that determine the fate of the airborne pollutants while special care is taken to ensure the availability of the required input data from routine observations or forecasts. The comparison between model predictions and actual observations shows a good agreement. In addition, a series of sensitivity tests is performed in order to evaluate the sensitivity of the model to the uncertainty in meteorological variables. Model forecasts are generally rather insensitive to small perturbations in most of the input meteorological data, while they are relatively more sensitive in changes in wind speed and direction.