N. Moussiopoulos

A numerical study of atmospheric pollutant dispersion in different two-dimensional street canyon configurations

Abstract The scope of this paper is to study numerically the dispersion of atmospheric pollutants within different street canyon geometrical configurations and building height scenarios. The microscale model MIMO, designed to take into account pollution dispersion in the vicinity of buildings, is validated against a two-dimensional wind-tunnel experiment for a square (W/H=1) and a deep canyon (W/H=1/2) configuration. It was found that the model performance is satisfactory. Having established this, the study involved the alteration of the building heights bounding the canyon for both square and deep configurations. Furthermore, the effects of different aspect ratios on the pollution dispersion characteristics are investigated. It is demonstrated that, under certain conditions, pollutants disperse more easily, while under others pollutant levels increase, with implications for pedestrian exposure. Furthermore, interaction of air in and above the canyons is investigated under different street geometries. It is found that both street geometry and building height influence the interaction between air inside and above the canyons.

The use of multi-criteria decision analysis to tackle waste management problems: a literature review.

Problems in waste management have become more and more complex during recent decades. The increasing volumes of waste produced and social environmental consciousness present prominent drivers for environmental managers towards the achievement of a sustainable waste management scheme. However, in practice, there are many factors and influences – often mutually conflicting – criteria for finding solutions in real-life applications. This paper presents a review of the literature on multi-criteria decision aiding in waste management problems for all reported waste streams. Despite limitations, which are clearly stated, most of the work published in this field is reviewed. The present review aims to provide environmental managers and decision-makers with a thorough list of practical applications of the multi-criteria decision analysis techniques that are used to solve real-life waste management problems, as well as the criteria that are mostly employed in such applications according to the nature of the problem under study. Moreover, the paper explores the advantages and disadvantages of using multi-criteria decision analysis techniques in waste management problems in comparison to other available alternatives.

Application of ELECTRE III for the integrated management of municipal solid wastes in the Greater Athens Area

Abstract The present work presents an application of multicriterial aid for decisions in the area of municipal solid waste management in Greece, in the context of a case study for household wastes in the Greater Athens Area. For the case study area, a concise family of 24 evaluation criteria is proposed. Through these, five selectively composed alternatives for the integrated management of household waste are compared and ranked by the ELECTRE III multicriterial method. Results indicate separate collection at the source to be particularly important, whereas the need for careful sensitivity analysis to inter- and intra-criteria information is demonstrated.

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

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

Increased biomass burning due to the economic crisis in Greece and its adverse impact on wintertime air quality in Thessaloniki.

The recent economic crisis in Greece resulted in a serious wintertime air pollution episode in Thessaloniki. This air quality deterioration was mostly due to the increased price of fuel oil, conventionally used as a source of energy for domestic heating, which encouraged the residents to burn the less expensive wood/biomass during the cold season. A wintertime sampling campaign for fine particles (PM2.5) was conducted in Thessaloniki during the winters of 2012 and 2013 in an effort to quantify the extent to which the ambient air was impacted by the increased wood smoke emissions. The results indicated a 30% increase in the PM2.5 mass concentration as well as a 2-5-fold increase in the concentration of wood smoke tracers, including potassium, levoglucosan, mannosan, and galactosan. The concentrations of fuel oil tracers (e.g., Ni and V), on the other hand, declined by 20-30% during 2013 compared with 2012. Moreover, a distinct diurnal variation was observed for wood smoke tracers, with significantly higher concentrations in the evening period compared with the morning. Correlation analysis indicated a strong association between reactive oxygen species (ROS) activity and the concentrations of levoglucosan, galactosan, and potassium, underscoring the potential impact of wood smoke on PM-induced toxicity during the winter months in Thessaloniki.

Simulation of the wind field in Athens using refined boundary conditions

Abstract The nested version of the prognostic mesoscale model MEMO was applied in the frame of the APSIS project to simulate air flow in Athens. By performing an additional simulation for an expanded model domain, this version allows imposing numerically computed boundary values at a higher temporal and spatial resolution. This approach is far superior compared to that of the non-nested version of MEMO, in the case of which lateral boundary conditions proved to have a significant influence on the surface flow field. In the present paper two days corresponding to two different meteorological situations are considered: 25 May 1990 (APSIS A) and 10 June 1987 (APSIS A′). While the former case is typical for stagnant conditions in Athens, the latter is characteristic for the sea breeze circulation in the area. Simulation results for 10 June 1987 are compared with available measurements. This comparison reveals that MEMO reproduces very satisfactorily the mesoscale flow pattern in Athens. Both investigated synoptic conditions are found to be favourable for the occurrence of air pollution episodes in Athens. Additionally it is proved that mesoscale flow results are rather sensitive to even small changes in large scale environment conditions.

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

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

Air quality in cities

Executive Summary.- 1: Introduction.- 2: Urban Air Pollution Phenomenology.- 3: Air Pollutant Emissions in Cities.- 4: Urban Field Campaigns.- 5: Particulate Matter in Urban Air.- 6: Modelling Urban Air Pollution.- 7: Quality Assurance of Air Pollution Models.- 8: Photochemical Smog in South European Cities.- 9: Integrated Urban Air Quality Assessment.- 10: Conclusions.- References.

Simulations of the wind field in Athens with the nonhydrostatic mesoscale model MEMO

Abstract MEMO is a fully vectorized nonhydrostatic mesoscale model using terrain-following coordinates. The numerical solution is based on second-order discretization applied on a staggered grid which is allowed to be non-equidistant in all directions. Special care is taken that conservative propeprties are preserved within the discrete model equations. The discrete pressure equation is solved with a direct elliptic solver in conjuction with a generalized conjugate gradient method. Advective terms are treated with an explicit, monotonicity-preserving discretization scheme with only small implicit diffusion. Turbulent diffusion is described using an one-equation turbulence model, while at roughness height similarity theory is applied. An efficient scheme is applied to calculate radiative transfer. The algebraic surface heat budget equation and an one dimensional heat conduction equation are solved to obtain the surface temperature over land and the soil temperature. In the frame of the APSIS exercise A the model MEMO was used to simulate the mesoscale flow in the Athens basin on May 25, 1990. Being in satisfactory agreement with observations, the results indicate that weak pressure gradients accompanied by warm advection aloft may lead to stagnant conditions and thus to severe air pollution episodes in Athens.

Comparing land use regression and dispersion modelling to assess residential exposure to ambient air pollution for epidemiological studies

BACKGROUND Land-use regression (LUR) and dispersion models (DM) are commonly used for estimating individual air pollution exposure in population studies. Few comparisons have however been made of the performance of these methods. OBJECTIVES Within the European Study of Cohorts for Air Pollution Effects (ESCAPE) we explored the differences between LUR and DM estimates for NO2, PM10 and PM2.5. METHODS The ESCAPE study developed LUR models for outdoor air pollution levels based on a harmonised monitoring campaign. In thirteen ESCAPE study areas we further applied dispersion models. We compared LUR and DM estimates at the residential addresses of participants in 13 cohorts for NO2; 7 for PM10 and 4 for PM2.5. Additionally, we compared the DM estimates with measured concentrations at the 20-40 ESCAPE monitoring sites in each area. RESULTS The median Pearson R (range) correlation coefficients between LUR and DM estimates for the annual average concentrations of NO2, PM10 and PM2.5 were 0.75 (0.19-0.89), 0.39 (0.23-0.66) and 0.29 (0.22-0.81) for 112,971 (13 study areas), 69,591 (7) and 28,519 (4) addresses respectively. The median Pearson R correlation coefficients (range) between DM estimates and ESCAPE measurements were of 0.74 (0.09-0.86) for NO2; 0.58 (0.36-0.88) for PM10 and 0.58 (0.39-0.66) for PM2.5. CONCLUSIONS LUR and dispersion model estimates correlated on average well for NO2 but only moderately for PM10 and PM2.5, with large variability across areas. DM predicted a moderate to large proportion of the measured variation for NO2 but less for PM10 and PM2.5.