Marina Astitha

Analysis of air quality observations with the aid of the source-receptor relationship approach

Abstract 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).

Heterogeneous Chemical Processes and Their Role on Particulate Matter Formation in the Mediterranean Region

The impact of particulate matter on air quality and the environment is an important subject for areas like the Greater Mediterranean Region, mostly due to the coexistence of major anthropogenic and natural sources. Such coexistence can create air quality conditions that exceed the imposed air quality limit values. Particulate matter formation and the factors enhancing or reducing such formation in the Mediterranean Region will be the primary focus of the work presented herein. Natural particulate matter appears mainly in the form of desert dust, sea salt and pollen among others and anthropogenic particulate matter appears as particulate sulfate and nitrate. The processes affecting the formation of new types of aerosols are based on the heterogeneous uptake of gases onto dust particles. New model development will be presented referring to the implementation of sea salt production and heterogeneous chemical processes leading to new aerosol formation in the photochemical model CAMx. Results from these simulations showed reasonable agreement with the available measurements. These results also revealed interesting effects of the coexistence of natural and anthropogenic particulate matter concerning the direct and indirect impacts on air quality and the environment.

Ten-year operational dust forecasting – Recent model development and future plans

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.

Mechanisms of Climate Variability, Air Quality and Impacts of Atmospheric Constituents in the Mediterranean Region

This chapter describes the physicochemical mechanisms that formulate the air quality over the Mediterranean region and the resulted impacts on the regional climate. At first, a detailed description of the teleconnections and regional flow patterns that dominate in the region is provided. The dominant flow patterns during the different seasons of the year determine the transport paths of air pollutants and aerosols towards and across the study area. The analysis on the characteristics of the air pollution transport is separated for the different parts of the Mediterranean region (eastern, western and entire), since the sources of pollutants that reach at different points in the region vary, while specific pollutant transport paths may influence the wider Mediterranean area. Similarities and differences in patterns are discussed. The air quality over the region, as recorded from black/organic carbon, ozone, aerosol observations, is extensively discussed, along with seasonal variabilities and annual trends. There is particular discussion on the suspension of naturally-produced aerosols and especially desert dust particles in the region and their spatial influence on the aerosol levels. At the last part of the chapter, the major impacts of the transport and transformation processes (natural and anthropogenic pollutants) on the regional climate are discussed. The impacts of aerosols are distinguished in direct (the impacts on radiation budget), health (the amounts of inhaled particles and impacts on health) and indirect effects (impacts on clouds and precipitation), are discussed on qualitative and quantitative way.

Issues Related to On/Offline Meteorological and Atmospheric Chemistry Model Coupling

The online approach consists of the coupled treatment of chemical parameters, simultaneously with the meteorological parameters, in a single integrated modeling system that is referred to as chemical weather modeling. This approach offers the possibility to simulate the links and feedbacks between atmospheric processes that are traditionally neglected in air quality models. Both meteorological and chemical components are expected to benefit from this approach. Both approaches have advantages and disadvantages that make their use appropriate for different applications. This study discusses and evaluates the performance of the online Integrated Community Limited Area Modeling System (RAMS/ICLAMS) and the offline model, Comprehensive Air Quality Model with Extensions (CAMx), for a month long retrospective summertime text period, over Europe and the Greater Mediterranean Area (GMR). The implementation of the same chemical mechanisms, meteorological fields, emissions, initial and boundary conditions makes it easier to compare the results from the two models. However, there are some differences in the physical parameterizations utilized in the two models that are expected to result in differences between them. The feedback mechanisms are not activated in order to evaluate the performance of the two models regarding the advantages that the online approach offers (same projection, no interpolation in time and space, explicit calculation of the meteorological components, availability of the meteorological fields at each time step etc.). Results showed that the online approach gave better results regarding ground 1 h ozone and 24 h sulfate aerosol concentrations improving the main statistical parameters by roughly 20 % and increased correlation from 0.51 to 0.70. The differences may be mainly the outcome of the utilization of different methods for the calculation of the photolysis rates and the interpolation of the meteorological data for use in the offline model.

An Online Coupled Two Way Interactive Modelling Study of Air Pollution Over Europe and Mediterranean

During the last decade, the efforts in the field of atmospheric modeling have been directed towards a joint ‘online’ approach of the meteorological and chemical processes in order to treat, in an integrated way, their complex and interactive links. This approach allows for the use of all meteorological fields as input in the chemical submodel, at each model time step, as well as takes into consideration the concentration of the pollutants on the meteorological processes (radiation and cloud microphysics). In this work, the air pollution over East Mediterranean is assessed with the use of the fully coupled, two-way interactive modeling system ICLAMS. Simulations have been performed for several test cases enhancing on the feedback mechanisms that occur. The summer case (July 2005) is used as base evaluation case due the increased insolation and high photolytic activity. The ozone model results are compared with measurements from stations from the European Monitoring and Evaluation Programme (EMEP). The correlation coefficient over all model domain reaches 0.7 with a root mean square error 22.78 μg/m3 and mean bias 0.74 μg/m3. The spring case (April 2004) highlights on the impact of mineral dust and sea salt on the photolysis rates that in turn determine the concentration of ozone in the area. The presence of dust over Finokalia station (Crete, Greece) leads to a decrease in the photolysis rates of NO2 and O3. Another winter case has also been discussed regarding the role of anthropogenic aerosols on clouds and precipitation.