Anna P. Protonotariou

Study of CO surface pollution in Europe based on observations and nested-grid applications of GEOS-CHEM global chemical transport model.

Carbon monoxide (CO) is studied over Europe for 2001 using measurements from 31 rural-background stations and the nested-grid application of the global CTM GEOS-CHEM. The model reveals lowest (highest) biases in warm (cold) periods, tracking observations in most cases more closely than the global model. The role of CO production and destruction processes and the atmospheric conditions are investigated. A rotated Principal Component Analysis is applied to all stations, based on daily CO modelled concentrations in 2001, yielding three principal components (PCs) with stations of common characteristics. CO concentrations are studied for these groups in relation to the circulation patterns prevailing over Europe in 2001, at mean sea level and 850 hPa. The nested-grid model improves results in comparison to those calculated by the global model by up to ∼22% for first principal component subregion, where emissions are high and elevation is low. Improvement reaches∼17 and∼7%, respectively, for second and third principal component subregions, where emissions are lower and altitudes are higher. Better performance is achieved for patterns associated with westerly flow, whereas poor skills are revealed during stagnant conditions. During pollution events, the nesting model’s ability in capturing CO surface concentrations improves by up to ∼40% in comparison to the global simulation.

Biomass Burning Aerosol Transport and Vertical Distribution over the South African-Atlantic Region

Optically thick smoke aerosol plumes originating from biomass burning (BB) in the southwestern African Savanna during the austral spring are transported westward by the free-tropospheric winds to primarily overlie vast stretches of stratocumulus cloud decks in the South-East Atlantic. We evaluated the simulations of long-range transport of BB aerosol by the Goddard Earth Observing System (GEOS-5) and four other global aerosol models over the complete South African-Atlantic region using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations to find any distinguishing or common model biases. Models in general captured the vertical distribution of aerosol over land, but exhibited some common features after long-range transport of smoke plumes that were distinct from that of CALIOP. Most importantly, the model simulated BB aerosol plumes quickly descend to lower levels just off the western coast of the continent, while CALIOP data suggests that smoke plumes continue their horizontal transport at elevated levels above the marine boundary layer. This is crucial because the sign of simulated aerosol semi-direct effect can change depending on whether the bulk of the absorbing aerosols are present within or above the cloud levels in a model. The levels to which the aerosol plumes get subsided and the steepness of their descent vary amongst the models as well as amongst the different sub-regions of the domain. Investigations into possible causes of differences between GEOS-5 and CALIOP aerosol transport over the ocean revealed a minimal role of aerosol removal process representation in the model as opposed to model dynamics.

European CO budget and links with synoptic circulation based on GEOS-CHEM model simulations

The European carbon monoxide (CO) budget is studied in relation to the synoptic circulation throughout 2001, using the nested-grid configuration of the GEOS-CHEM global model and CO measurements from 31 rural background stations. To meet the aims of this study, a seasonal circulation type (CT) classification is developed for the Northern Hemisphere based on mean sea-level pressure (SLP) fields, as well as two upper atmospheric levels, over a 60-yr period. The highest contribution to the European surface CO concentrations is attributed to regional anthropogenic sources (up to ~80%), which become more important under the prevalence of anticyclonic circulation conditions. The corresponding contribution of the long-range transport (LRT) from North America (up to 18%) and Asia (up to 20%) is found highest (lowest) in winter and spring (summer and autumn). The transport of the CO towards Europe in winter is more intense under cyclonic circulation, while both cyclonic and anticyclonic patterns favour LRT during other seasons. Occasionally (mainly in winter and spring), LRT contribution is higher than the regional one (up to 45%). In the free troposphere, the LRT contribution increases, with the largest impact originating from Asia. This flow is favoured by the intense easterly circulation in summer, contributing up to 30% in the Eastern Mediterranean during this season. On the other hand, the regional contribution in the upper levels decreases to 22%. The contribution of CO chemical production is significant for the European CO budget at all levels and seasons, exceeding 50% in the free troposphere during summer.

Physical and Chemical Processes of Polluted Air Masses During Etesians: Aegean-Game Airborne Campaign – An Outline

Gaseous species and aerosol size distribution and chemical composition within the boundary layer during the Etesians is investigated, based upon airborne measurements, over the Aegean Sea, from Crete to Limnos islands (29/8–8/9 2011, Aircraft_BAe146–FAAM). Three flights of a similar route covered the eastern and western parts of the Aegean Sea. Two flights were performed on the same day to study the impact of the diurnal cycle. The sorties involved horizontal tracks mainly at 150 m a.s.l. and above the aerosol layer, at 2.5 km a.s.l., and profiles up to 4.5 km near the ground stations of Crete and Limnos and the Central Aegean Sea. Marked variations were detected in the vertical structure of aerosols and thermodynamic variables between the eastern and western segments flown around the Aegean. Several discrete aerosol layers, separated by a clean slot, containing particles of different chemical composition were observed, with sulfates and organics being the dominant components. CO concentrations ranged from 80 ppb above the mixing layer, up to 140 ppb near the surface. O3 ranged between 50 and 75 ppb, with higher values observed at surface upwind of Finokalia and in the mixing layer in Central and Northern Aegean Sea.

Evaluation of CALPUFF modelling system performance: an application over the Greater Athens Area, Greece

This study has been carried out in order to evaluate the performance of CALPUFF modelling system in an area of complex topography. For this reason a comparison was performed between numerical results produced by this modelling system and those derived by two Eulerian models (UAM-V and REMSAD), together with experimental measurements. The meteorological input parameters, produced by the meteorological model CALMET are also examined through comparison with observations and to MM5 model results. Emphasis is given to the mixing height calculation, due to its importance in the prediction of pollutant concentrations. It was found that the overall performance of the CALPUFF is satisfactory and the results derived are compatible with these produced by the Eulerian models, especially under unstable atmospheric conditions. The CALPUFF models performance is improved significantly when vertical meteorological profiles produced by MM5 are additionally employed.

Comparison of data fusion methods for satellite-assisted determination of PM10 ambient concentration

Our recent work has demonstrated the feasibility of using satellite-derived data to draw quantitative maps of particulate loading within the planetary boundary layer. Our method, when used in conjunction with atmospheric dispersion models and ground data, can provide a comprehensive estimate of tropospheric pollution from particulate matter. Information filtering techniques are used to reduce the error of the information fusion algorithm and, consequently, produce the best possible estimate of tropospheric aerosol. Two data filtering methods have been used and their effectiveness with regard to overall error reduction is determined in this work. The first one is based on a weight scheme to take into account an empirical estimate of local error and/or uncertainty in input data. The second uses a modified Kalman filter for error reduction. The effectiveness of each of the filtering techniques depends on factors such as relative error variance across the computational domain, and precision of model input, i.e. on the accuracy of the ground emissions inventory and the reliability of measured ambient aerosol concentrations. The ICAROS NET fusion method was applied in the greater area of Athens, Greece over several days of observation in order to assess conclusively the adequacy of the information fusion filters employed.

Air Pollution in Eastern Mediterranean: Nested-Grid GEOS-CHEM Model Results and Airborne Observations

Trace gases concentrations in the boundary layer (BL) and the free troposphere are studied in the Eastern Mediterranean based on an updated nested-grid application of GEOS-CHEM global model and airborne observations that were collected over the Greek territory during the AEGEAN GAME airborne field campaign in September 2011. Modelled concentrations are studied against measurements along the flight tracks. Moreover, the spatial distribution of the pollutants over the study domain is examined in relation to the prevailing wind regime. The role of the long-range transport of pollution is investigated particularly through the northern and eastern boundaries due to the prevailing NE circulation. It is found that the model captures adequately carbon monoxide (CO) and ozone (O3) levels within the troposphere. CO and O3 concentrations over the Aegean Sea can exceed the background levels attributed either to transport downwind the local sources or to long range transport particularly from the northern and eastern part of the domain under the strong NE Etesian winds.