Characteristic scales of transport and transformation of air pollutants - possible impacts on climate

The main purpose of this work has been the study of the production, transformation and transport processes of atmospheric pollutants in the Mediterranean Region. This region is considered a key-sensitive area due to the unique climatic and air quality characteristics associated with the regional climatic patterns, the geomorphology and the coexistence of pollutants from different origin. The Mediterranean Region including the Saharan desert and important part of Europe is very often influenced by high levels of desert dust, long-range transport of pollutants from Europe and intense photochemical activity, leading to atmospheric pollutant concentrations higher than the imposed EU limit values. The processes occurring along the characteristic paths of transport, the production of various generations of pollutants and the role of mineral dust and sea-salt are under consideration in this study. The modeling tools have been revised accordingly by the development and improvement of several physico-chemical mechanisms. In particular, the new development included the impacts of desert dust on photochemical processes, the sea salt particle production and the treatment of soil dust particles as reactive agents (through the incorporation of heterogeneous chemical processes). Sensitivity tests have been carried out for each part of the development, supporting the fact that high concentrations of desert dust can reduce the photolysis rates and cause reduction of ozone and sulfate concentration (5% and 10% of the concentration without the dust influence, respectively). The implementation of the heterogeneous reactions on dust particles has revealed changes in the gaseous and particulate pollutant concentrations that, in several cases, enhanced the model performance. Large-scale model simulations have been performed for April and August, in order to better understand the transport and transformation patterns over large distances from the origin of various pollutants. The results from these simulations delineated the sensitivity of the region to the coexistence of natural and anthropogenic pollutants. The paths followed by the pollutants are driven by the meteorological conditions, as already known. The composition of the air masses though, is subject to changes because of the chemical transformations that occur during their journey. In that way, the air masses reaching Africa are enriched with 3rd generation pollutants apart from the pure natural or anthropogenic species. The average concentration of the aerosol species (sulfates, nitrates, sodium, chloride and dust) calculated for the specific simulation domain showed the dominance of sulfates and nitrates in the size section of 0.1-2.5μm (diameter), and the dominance of dust, sodium and chloride in the coarser fraction. Combining this information with the capability of each species to affect solar radiation (absorption, scatter, extinction) and taking into account their deposition pathways, interesting insights can emerge on the potential climatic and environmental impacts for the Mediterranean Region.Ο στόχος της παρούσας διατριβής είναι η μελέτη των μηχανισμών παραγωγής, μετασχηματισμού και μεταφοράς ατμοσφαιρικών ρύπων στην ευρύτερη περιοχή της Μεσογείου. Η περιοχή αυτή χαρακτηρίζεται ως ιδιαίτερης ευαισθησίας λόγω των μοναδικών κλιματικών χαρακτηριστικών και της ποιότητας της ατμόσφαιρας τα οποία συνδέονται με τη γεωμορφολογία της περιοχής και τη συνύπαρξη ρύπων διαφορετικής προέλευσης. Η περιοχή της Μεσογείου συμπεριλαμβανομένης της ερήμου Σαχάρα και σημαντικού μέρους της Βορείου Ευρώπης εκτίθεται συχνά σε αυξημένες συγκεντρώσεις σκόνης, σε μεγάλης κλίμακας μεταφορά αέριων ρύπων από την υπόλοιπη Ευρώπη και σε έντονη φωτοχημική δραστηριότητα, οδηγώντας πολύ συχνά τις συγκεντρώσεις αρκετά πιο ψηλά από τα όρια που έχουν τεθεί από την Ευρωπαϊκή Ένωση. Οι διαδικασίες που πραγματοποιούνται κατά τη διάρκεια της μεταφοράς των ατμοσφαιρικών ρύπων, η παραγωγή ρύπων διαφορετικής γενιάς και ο ρόλος της ερημικής σκόνης και του θαλασσινού αλατιού είναι τα θέματα που λαμβάνονται υπόψη και αναλύονται στην παρούσα διατριβή. Η ανάπτυξη των αριθμητικών μοντέλων συνίσταται στη μοντελοποίηση της επίδρασης της ερημικής σκόνης στους ρυθμούς φωτόλυσης των φωτοχημικών αντιδράσεων, της παραγωγής του θαλασσινού αλατιού ως αερόλυμα μέσα στο μοντέλο ατμοσφαιρικής χημείας και της διαχείρισης των σωματιδίων σκόνης ως πυρήνων εναπόθεσης αέριων ρύπων (ετερογενείς αντιδράσεις πάνω σε σωματίδια σκόνης). Σε κάθε στάδιο της ανάπτυξης πραγματοποιήθηκαν τεστ ευαισθησίας, τα οποία κατέδειξαν πως οι μεγάλες συγκεντρώσεις ερημικής σκόνης μπορούν να μειώσουν τους ρυθμούς φωτόλυσης με αποτέλεσμα τη μείωση του τροποσφαιρικού όζοντος και των θειικών σωματιδίων (μείωση 5% και 10% της συγκέντρωσης χωρίς την επίδραση της σκόνης, αντίστοιχα). Οι ετερογενείς αντιδράσεις πάνω στα σωματίδια ερημικής σκόνης έδειξαν μεταβολές στη συγκέντρωση των αέριων και σωματιδιακών ρύπων, οι οποίες σε αρκετές περιπτώσεις βελτίωσαν την απόδοση του μοντέλου. Μεγάλης κλίμακας προσομοιώσεις πραγματοποιήθηκαν για τον Απρίλιο και τον Αύγουστο, καλύπτοντας μια ευρεία περιοχή από τη Βόρεια Ευρώπη ως την Νότια Αφρική και από την Αραβική χερσόνησο μέχρι τον Ατλαντικό Ωκεανό. Οι προσομοιώσεις αυτές, έχοντας συμπεριλάβει τις νέες φυσικοχημικές διεργασίες, έδειξαν την ευαισθησία της περιοχής στη συνύπαρξη ρύπων ανθρωπογενούς και φυσικής προέλευσης. Η πορεία που ακολουθούν οι ατμοσφαιρικοί ρύποι επηρεάζεται όπως είναι γνωστό από τις επικρατούσες μετεωρολογικές συνθήκες, αλλά η χημική σύσταση των ρύπων μεταβάλλεται λόγω των χημικών μετασχηματισμών που συμβαίνουν κατά το ταξίδι τους. Με αυτό τον τρόπο, οι αέριες μάζες που καταλήγουν στην Αφρική περιέχουν τρίτης γενιάς ρύπους εκτός από τους ανθρωπογενείς και φυσικούς. Η μέση συγκέντρωση θειικών και νιτρικών αερολυμάτων στην περιοχή της προσομοίωσης έδειξε να έχει μέγιστο στο μεσαίο διαμετρικό μέγεθος (0.1-2.5μm), ενώ η ερημική σκόνη, το νάτριο και το χλώριο κυριαρχούν στα μεγαλύτερα μεγέθη. Συνδυάζοντας αυτές τις πληροφορίες με την ικανότητα κάθε ρύπου να επηρεάζει την ηλιακή ακτινοβολία και λαμβάνοντας υπόψη την εναπόθεσή τους, μπορούν να προκύψουν ενδιαφέροντα συμπεράσματα για τις πιθανές κλιματικές επιπτώσεις στην περιοχή της Μεσογείου

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

On Predicting Offshore Hub Height Wind Speed and Wind Power Density in the Northeast US Coast Using High-Resolution WRF Model Configurations during Anticyclones Coinciding with Wind Drought

We investigated the predictive capability of various configurations of the Weather Research and Forecasting (WRF) model version 4.4, to predict hub height offshore wind speed and wind power density in the Northeast US wind farm lease areas. The selected atmospheric conditions were high-pressure systems (anticyclones) coinciding with wind speed below the cut-in wind turbine threshold. There are many factors affecting the potential of offshore wind power generation, one of them being low winds, namely wind droughts, that have been present in future climate change scenarios. The efficiency of high-resolution hub height wind prediction for such events has not been extensively investigated, even though the anticipation of such events will be important in our increased reliance on wind and solar power resources in the near future. We used offshore wind observations from the Woods Hole Oceanographic Institution’s (WHOI) Air–Sea Interaction Tower (ASIT) located south of Martha’s Vineyard to assess the impact of the initial and boundary conditions, number of model vertical levels, and inclusion of high-resolution sea surface temperature (SST) fields. Our focus has been on the influence of the initial and boundary conditions (ICBCs), SST, and model vertical layers. Our findings showed that the ICBCs exhibited the strongest influence on hub height wind predictions above all other factors. The NAM/WRF and HRRR/WRF were able to capture the decreased wind speed, and there was no single configuration that systematically produced better results. However, when using the predicted wind speed to estimate the wind power density, the HRRR/WRF had statistically improved results, with lower errors than the NAM/WRF. Our work underscored that for predicting offshore wind resources, it is important to evaluate not only the WRF predictive wind speed, but also the connection of wind speed to wind power

Investigating the Coherence Between a Global and a Limited Area Model for Dust Particle Production and Distribution in N-Africa

The choice of the parameterization scheme, the input parameters and the spatial resolution are options that can provide significantly different modelling results for the processes of desert dust production and transport. This work will discuss the level of coherence between a regional and a global modelling system with regards to the simulation of desert dust production and transport in N-Africa. The limited-area model SKIRON/Dust and the atmospheric chemistry general circulation model EMAC (ECHAM5/MESSy2 Atmospheric Chemistry) have been applied using a common physically-based dust emission scheme. The differences between the two modelling systems and the comparison with the observations will be analysed and discussed, as well as the plans for future work in their offline coupling

The Role of Aerosols in Low and Upper Atmospheric Layers Condensation

Airborne particles of anthropogenic and/or natural origin have certain direct and indirect effects in the atmosphere. Radiative transfer is the category of processes related to aerosols and clouds (direct effects). Indirect effects are always associated with condensates at various atmospheric layers. Condensation within the tropospheric layers is mainly related to aerosol physical and chemical properties, thermodynamical and dynamical processes. As it was found in various studies, there is a strong relationship between aerosols and extreme weather events such as deep convection and extreme rainfall. Low-level condensation is associated with low-cloud formation and fog. In this presentation we will discuss the condensation processes within the lower and upper troposphere and how they are affected by the various types of aerosols. New model development related to nucleation processes and condensation at different levels is discussed. The model used for development and application is the fully-coupled atmospheric modeling system RAMS/ICLAMS. Model simulations have been performed for selected cases related to (i) extreme precipitation events and (ii) low-level condensation and fog formation in the Euro-Mediterranean and Arabian Peninsula. The sensitivity tests showed that the explicit activation of aerosols as CCN and IN causes changes in the precipitation distribution as well as in its spatiotemporal patterns. Fog formation near the coastline and low-cloud formation mechanisms are controlled by the thermal cooling and moisture evaporation by the surface. The accurate simulation of the microphysical processes involved in formation and dissipation of fog depends on several variables

Saharan dust levels in Greece and received inhalation doses

The desert of Sahara is one of the major sources of mineral dust on Earth, producing around 2×10<sup>8</sup> tons/yr. Under certain weather conditions, dust particles from Saharan desert get transported over the Mediterranean Sea and most of Europe. The limiting values set by the directive EC/30/1999 of European Union can easily be exceeded by the transport of desert dust particles in the south European Region and especially in urban areas, where there is also significant contribution from anthropogenic sources. In this study, the effects of dust transport on air quality in several Greek urban areas are quantified. PM<sub>10</sub> concentration values from stationary monitoring stations are compared to dust concentrations for the 4-year period 2003–2006. The dust concentration values in the Greek areas were estimated by the SKIRON modelling system coupled with embedded algorithms describing the dust cycle. The mean annual dust contribution to daily-averaged PM<sub>10</sub> concentration values was found to be around or even greater than 10% in the urban areas throughout the years examined. Natural dust transport may contribute by more than 20% to the annual number of exceedances – PM<sub>10</sub> values greater than EU limits – depending on the specific monitoring location. In a second stage of the study, the inhaled lung dose received by the residents in various Greek locations is calculated. The particle deposition efficiency of mineral dust at the different parts of the human respiratory tract is determined by applying a lung dosimetry numerical model, which incorporates inhalation dynamics and aerosol physical processes. The inhalation dose from mineral dust particles was greater in the upper respiratory system (extrathoracic region) and less significant in the lungs, especially in the sensitive alveolar region. However, in cases of dust episodes, the amounts of mineral dust deposited along the human lung are comparable to those received during exposure in heavily polluted urban or smoking areas

Integrated Study of Dust-air Pollution Interaction over the Eastern Mediterranean

Interactions of desert dust and air pollution over the Eastern Mediterranean (EM) have been studied, focusing on two distinct dust transport events on 22 and 28 September 2011. The atmospheric chemistry-climate model EMAC has been used at about 50 km grid spacing on global scale, applying an online dust emission scheme and calcium as a proxy for dust reactivity. EMAC includes a detailed tropospheric chemistry mechanism, aerosol microphysics and thermodynamics schemes to describe dust" aging''. The model is evaluated using ground-based observations for aerosol concentrations and aerosol optical depth, LIDAR as well as satellite observations. Simulation results and back trajectory analysis show that the development of synoptic disturbances over the EM can enhance dust transport from the Sahara and Arabian deserts in frontal systems that also carry air pollution to the EM

Dynamics of fine particles and photo-oxidants in the Eastern Mediterranean

Summarization: As part of the European project SUB-AERO, comprehensive aerosol and gaseous pollutant measurement campaigns were performed at the Finokalia station (July 2000 and January 2001) on the island of Crete (Greece) in combination with boat measurements in the eastern part of the Mediterranean area. The measurements were performed with the participation of nine European research institutions. The objective of the measurement campaigns was to evaluate and assess the spatial and temporal variability of photochemical pollutants and fine particles. The current overview paper presents the framework and main results of the measurements and modelling studies performed during the project. Extensive measurements of gaseous and atmospheric-aerosol physical, chemical and optical characteristics were performed during the measurement campaigns in conjunction with detailed chemical analyses of the aerosol species. Along with the experimental work mesoscale modelling, using a combination of the UAM-AERO air quality model together with the RAMS prognostic meteorological model, was used to reveal the dynamics of particulate matter and photo-oxidants. Furthermore, regional chemistry transport models were applied to determine the background and initial conditions for the mesoscale modelling.Presented on: Atmospheric environmen