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The climatic conditions in the Greater Mediterranean Region (GMR) are known to have significant regional scale characteristics capable of long-range transport. The climatic patterns and the physiographic characteristics of the Mediterranean Region, forces the air quality in the area to exhibit remarkable spatiotemporal variability. In addition, concentrations of various pollutants (primary and/or secondary) are found to be significant in remote locations as well as in multiple-layer structures up to a few kilometers above the surface. For the GMR, besides the production, the term of transport of tropospheric ozone and its precursors should be of great interest, as well as the role of ozone in the production of several other pollutants, such as mercury. During the last years, a great number of studies also focus on the important role of aerosols in the air quality of a specific area, due to the potential impact on human health and ecosystems. Desert dust is one of the crucial components that contribute to the air quality degradation of the GMR. Due to these facts the aerosol concentration and deposition patterns are of great interest, along with ozone and its precursors, especially efforts for predicting air quality degradation episodes.

“How can we assimilate detailed information from the urban canopy into regional models?” That is the question to be addressed in this contribution. In regional air quality models the exchange of pollutants between the surface and the atmosphere is generally represented by an emission source term and a deposition term. It is common practise that emissions generated at the surface are instantaneously diffused into the grid cells. Many of the dynamics of the urban canopy are not represented in regional models despite the fact that we have a lot of detailed information about these dynamics, e.g. on the canopy structure and roughness elements, on traffic emissions and on street canyon dynamics (Vardoulakis et al., 2003). In particular road transport emissions can be described hourly as a function of the road type, vehicle type, fuel type, traffic volume, vehicle age, trip length distribution and the actual ambient temperature (Mensink et al, 2000).

Many city intersections are often heavily polluted due to intensive traffic. Dispersion of pollutants originating from traffic is directly connected with the geometry of the urban area and traffic conditions. The urban area is mostly heavily built-up area and buildings and other obstacles that may significantly influence local concentrations. Moving vehicles enhance both micro- and large-scale mixing processes in their surroundings. Not taking into account traffic will lead to neglecting one of the most important phenomena that influences mixing processes in the proximity of traffic paths. The influence of traffic is increasingly important in situations of very low wind speed.

In recent years, there has been a growing realization that regional-scale ozone (O3) air quality is influenced by processes occurring on global scales, such as the intercontinental transport of pollutants (Jacob et al., 1999; Fiore et al., 2002, 2003; Yienger et al., 2000) and the projected growth in global emissions that alter the chemical composition of the global troposphere (Prather and Ehhalt, 2001; Prather et al., 2003). However, little work has been performed to date to study the potential impacts of regional-scale climate change on near-surface air pollution. Climate change can influence the concentration and distribution of air pollutants through a variety of direct and indirect processes, including the modification of biogenic emissions, the change of chemical reaction rates, changes in mixedlayer heights that affect vertical mixing of pollutants, and modifications of synoptic flow patterns that govern pollutant transport. Another parameter affecting local and regional meteorology and air pollution is land use, and significant land use changes associated with continued urbanization are expected to occur over the same time scales as changes in regional climate.

Depending on their chemical composition, sizes and shapes, aerosol particles may scatter and absorb solar radiation and act as nuclei for condensation of water vapour and for freezing of water droplets. Availability of cloud condensation (CCN) and ice nuclei (IN) is responsible for the realized water vapour super-saturations in the troposphere. Human activity inadvertently produces aerosol particles. Production mechanisms include combustion of fossil fuels and biomass, leading to submicron particles containing sulphate, nitrate, black carbon and particulate organic matter. These compounds typically reside up to a week in the troposphere and the mixing ratios have considerable gradients. Depending on their composition as a function of size and shape, particles may scatter and absorb solar radiation and act as CCN. Anthropogenic changes in these properties may directly produce radiative forcing, or indirectly through changes in cloud properties. Considerable attention has been paid to the potential climate influence of anthropogenic particles (e.g. Charlson ., 1987; Wigley, 1989; Charlson . 1991; Kiehl and Briegleb, 1993). There is considerable incertitude associated with its quantification, and in particular the indirect effect (Houghton ., 2001).

Aerosol formation in the remote marine atmosphere and its effect on climate has been an area of intense study as a negative feedback to warmer surface oceans. Fine aerosols form cloud condensation nucleii (CCN) and scatter incident radiation back to space. Charlson ., 1987 proposed that dimethylsulphide (DMS), a gas released from the ocean during turnover of microalgae populations in the ocean’s surface, and its oxidation products including sulphur dioxide (SO2) were crucial pieces to understanding the global climate puzzle.

Recently there have been significant improvements with respect to aerosol modelling. Models with 1-atmosphere approach are able to simulate both gaseous and particulate pollutants and suitable for episodic and annual calculations (Ackermann et al., 1998; Schell et al., 2001). There are also more complete models including full-science algorithms for aerosol modelling (Griffin et al., 2003; Bessagnet et al., 2004; Zhang et al., 2004). However, such models are more complex and demanding. A model intercomparison study showed that a more complex model approach to the aerosol problem does not automatically lead to better results in a 3-dimensional application (Hass et al., 2003). As long as speciated aerosol measurements with high time resolution are limited, the necessity of using so called full-science aerosol models is questionable. In this study, two air quality models with different approaches were applied to two domains, northern Italy and Switzerland, to investigate the capabilities, strengths and weaknesses.

A substantial fraction of fine particulate matter (PM) across the United States is composed of carbon, which may be either emitted in particulate form (i.e., primary) or formed in the atmosphere through gas-to-particle conversion processes (i.e., secondary). Primary carbonaceous aerosol is emitted from numerous sources including motor vehicle exhaust, residential wood combustion, coal combustion, forest fires, agricultural burning, solid waste incineration, food cooking operations, and road dust. Quantifying the primary contributions from each major emission source category is a prerequisite to formulating an effective control strategy for the reduction of carbonaceous aerosol concentrations. A quantitative assessment of secondary carbonaceous aerosol concentrations also is required, but falls outside the scope of the present work.

In the last years, there has been an increase of scientific studies confirming that long- and short-term exposure to particulate matter pollution leads to adverse health effects. The determination of accumulated human exposure in urban areas (in the present study focused on Lisbon) is the main objective of the current work combining information on concentrations at different microenvironments and population timeactivity pattern data. A link between a mesoscale meteorological model and a local scale model (Computational Fluid Dynamics’ based) was developed to define the boundary conditions for the local scale application. The time-activity pattern of the population was derived from statistical information for different sub-population groups and linked to digital city maps. Finally, the hourly PM10 concentrations for indoor and outdoor microenvironments were estimated for the Lisbon city centre based on the local scale air quality model application for a chosen day.

In winter and summer of 2000 field experiments were conducted to investigate the physical and chemical evolution of two different plume sources, one is a copper smelter in Quebec and the other is a coal-fired power plant in Ontario. The field experimental data was used to support a modelling study of the transport and deposition of particulate metals from these industrial sources. The purpose of this study is to investigate the particle size dependent concentration and deposition patterns of current emissions of particulate metals and to estimate the proportion subject to long range transport.