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?European CO budget and links with synoptic circulation in accordance with GEOS-CHEM product simulations
European CO budget and links with synoptic circulation in accordance with GEOS-CHEM product simulations
By ANNA P. PROTONOTARIOU 1 *. EFFIE KOSTOPOULOU two. MARIA TOMBROU 1 and CHRISTOS GIANNAKOPOULOS 3 ,  1 Division of Environmental Physics and Meteorology, Department of Physics, National and Kapodistrian University of Athens, Generating V, 157 84, Athens, Greece;  two Department of Geography, University within the Aegean, University Hill, Mytilene, GR 81100, Greece;  3 Institute for Environmental Research and Sustainable Enhancement, National Observatory of Athens, V. Pavlou and Metaxa Str. GR-15236, Palaia Pendeli, Athens, Greece
(Manuscript received 6 May 2012; in final variety eleven March 2013; published twenty five April 2013)
The European carbon monoxide (CO) budget is studied in relation to the synoptic circulation throughout 2001, utilising the nested-grid configuration in the GEOS-CHEM world-wide product and CO measurements from 31 rural background stations. To meet the aims of this study, a seasonal circulation type (CT) classification is developed for your Northern Hemisphere depending on mean sea-level pressure (SLP) fields, also as two upper atmospheric stages, over a 60-yr period. The highest contribution to the European surface CO concentrations is attributed to regional anthropogenic resources (up to
80%), which become much more important beneath the prevalence of anticyclonic circulation conditions. The corresponding contribution of your 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 belonging to the CO towards Europe in winter is increased intense below cyclonic circulation, while you are the two cyclonic and anticyclonic patterns favour LRT during other seasons. Occasionally (mainly in winter and spring), LRT contribution is higher than the regional an individual (up to 45%). During the 100 % 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% inside of the Eastern Mediterranean during this season. Within the other hand, the regional contribution around the upper stages decreases to 22%. The contribution of CO chemical production is significant for your European CO budget in anyway amounts and seasons, exceeding 50% from the no charge troposphere during summer.
Keywords: Europe, atmospheric circulation, carbon monoxide, long-range transport, intercontinental design
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Tellus B 2013. © 2013 A. P. Protonotariou et al. This is undoubtedly an Open Obtain article distributed underneath the terms belonging to the Creative Commons Attribution-Noncommercial 3.0 Unported License (http://creativecommons.org/licenses/by-nc/3.0/ ), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original get the job done is properly cited.
Citation: Tellus B 2013, 65 . 18640, http://dx.doi.org/10.3402/tellusb.v65i0.18640
1. Introduction
The estimation of carbon monoxide (CO) concentrations can be described as complex problem, dependent strongly on fossil fuel, biofuel and biomass burning emissions, the oxidation of methane (CH four ) and non-methane volatile compounds (NMVOCs) and then the hydroxyl radical (OH) (Allen et al. 1996 ; Kanakidou et al. 1999 ; Holloway et al. 2000 ; Duncan and Logan, 2008 ). The atmospheric circulation also has a dominant role to the pollutant degrees since several CO pollution events and large-scale horizontal gradients have been associated with the prevailing atmospheric conditions (Chung et al. 1999 ; Wang et al. 2004a ; Liu et al. 2006 ; Drori et al. 2012 ).
Due to the CO lifetime inside of the troposphere (30–90 d), the pollutant may very well be transported in continental scales through several pathways (Holloway et al. 2000 ; Li et al. 2002 ; Liu et al. 2003 ; Duncan and Bey, 2004 ; Huntrieser and Schlager, 2004 ; Liang et al. 2004 ; Weiss-Penzias et al. 2004 ; Auvray and Bey, 2005 ; Drori et al. 2012 ). The transatlantic long-range transport (LRT) is particularly favoured due to the relatively short distance relating to North America and Europe. The transport of air from North America towards Europe takes spot during the troposphere throughout the calendar year, following the general circulation over the North Atlantic (Wild and Akimoto, 2001 ; Stohl et al. 2003a. 2003b ). Around the lower troposphere (LT), these transport paths are determined by the strength and also position on the Azores Huge, in blend with the Icelandic Lower (Li et al. 2002 ; Auvray and Bey, 2005 ; Christoudias et al. 2012 ). Within the completely free troposphere, the transatlantic LRT takes put when air masses from the North American surface are lifted to the upper amounts through mid-latitude cyclones and convection; then, the pollutants are transported towards Europe, governed primarily by the westerly circulation in addition to the jet streams (Stohl, 2001 ; Cooper et al. 2002 ; Li et al. 2002. 2005 ; Trickl et al. 2003 ; Huntrieser and Schlager, 2004 ). Similarly, the LRT from Asia towards Europe occurs throughout the 12 months when mid-latitude cyclones and deep convection lift the pollutants into the free of charge troposphere (Liu et al. 2003 ; Auvray and Bey, 2005 ). Another export pathway from Asia that directly affects Europe is observed from the conclusion of May until the stop of August and is related using an upper easterly present-day extending to the west across South Arabia and North Africa (Barry and Chorley, 2003 ; Auvray and Bey, 2005 ). As a result, the Asian pollution has frequently been detected not only inside upper troposphere (UT) but also inside the LT over the Eastern Mediterranean (Lelieveld et al. 2002 ; Lawrence et al. 2003 ; Roelofs et al. 2003 ; Scheeren et al. 2003 ; Traub et al. 2003 ; Drori et al. 2012 ). Over the other hand, the transport from the rest on the world towards Europe isn't really favoured due to the presence in the Inter-tropical Convergence Zone (ITCZ). Some pollution of African origin has actually been detected mostly around the Mediterranean region, as transport from Australia and South America to Europe has rarely been reported (Stohl et al. 2002 ; Roelofs et al. 2003 ; Kallos et al. 2006. 2007 ).
The combustion in the fossil fuels and also the biofuels in Asia, North America and Europe dominates the surface CO distribution while in the Northern Hemisphere (NH) (Fig. 1. Table 1 ). The majority on the anthropogenic resources are located inside of a mid-latitude belt relating to 30°N and 65°N, where the population density in addition to the anthropogenic activity are huge (Schultz and Bey, 2004 ). Africa and South America represent the world regions with the highest biomass burning emissions globally. However, it should be noted that the biomass burning activity is substantial also around the Mediterranean and Eastern Europe during the summer. Moreover, the CO chemical production by the oxidation of CH four and NMVOCs can be significant to the pollutant's concentration degrees in just the troposphere.
Table 1.  Longitude and latitude of source regions proven in Fig. 1 and corresponding CO fossil fuel-biofuel/biomass burning emissions (Tg(CO)/yr) on seasonal basis in GEOS-CHEM as considered on this study
The world-wide chemical transport models (CTMs) have proved to be suitable applications to reproduce the observed CO in extended scales (Kanakidou and Crutzen, 1999 ; Holloway et al. 2000 ; Tanimoto et al. 2009 ). Regarding the European domain, simulations within the world CTMs MOZART-2 (Pfister et al. 2004 ) and MATCH-MPIC (Fischer et al. 2006 ) revealed that the predominant contribution to the surface CO stages over Europe is attributed to the regional emissions. Over the contrary, it was found that most of your CO while in the European middle troposphere (MT) and UT is transported from Asia and North America. These successes are consistent with those of other studies that emphasised about the Eastern Mediterranean (Lelieveld et al. 2002 ; Lawrence et al. 2003 ; Drori et al. 2012 ).
In order to track the CO origin, its molecules could possibly be tagged according to the type as well as location of its primary emission resources together with the chemical production. This tagging technique may be carried out within the world wide CTM GEOS-CHEM (Bey et al. 2001a. 2001b ) and its nested-grid software at the same time (Wang et al. 2004a. 2004b ). Previous studies have employed the nested-grid configuration of this product in several world regions this kind of as Asia (Wang et al. 2004a. b. 2009b ; Chen et al. 2009 ), North America (Fiore et al. 2005 ; Li et al. 2005 ; Park et al. 2006 ; Wang et al. 2009a ; Zhang et al. 2011 ) and Europe (Protonotariou et al. 2010 ). The nesting successes indicated that the representation in the pollutants improves in comparison to the world product, particularly for certain regions (e.g. huge emission intensity, complex terrain) and time periods (e.g. pollution events).
World wide simulations for the GEOS-CHEM product have previously been employed to study transport of O 3 and CO towards Europe (Li et al. 2002 ; Auvray and Bey, 2005 ; Guerova et al. 2006 ), but the European CO concentrations haven't systematically been studied in relation to the synoptic circulation. Within the current study, an analysis for the CO budget in just the European troposphere in relation to the atmospheric circulation is carried out for your 1-yr period of 2001, dependant on the nested-grid software for the GEOS-CHEM. To this aim, a fairly recently developed circulation-pattern classification scheme over the NH is presented along with the contribution of direct surface emissions from all continents and also the chemical production are estimated inside of the LT, the MT and also the UT during winter and summer of 2001 according to tagged CO simulations. Furthermore, dependant upon Principal Component Analysis (PCA), the LRT contribution towards Europe is examined in relation to the atmospheric circulation at three station sites, where the surface CO measurements are obtainable for your examined period (Air Good Databases belonging to the European Environmental Agency; http://www.eea.europa.eu/data-and-maps/data/airbase-the-european-air-quality-database-1 ).
two. Methodology
two.1. The GEOS-CHEM design description
GEOS-CHEM can be described as three-dimensional international atmospheric CTM (Bey et al. 2001b ) developed by the Atmospheric Chemistry Modelling Group of Harvard University (http://acmg.seas.harvard.edu/ ). In such a study, the nested-grid configuration belonging to the model's version 07-01-02 is applied over Europe (Protonotariou et al. 2010 ). Assimilated meteorological details from the Goddard Earth Observing Model (GEOS) for the NASA Intercontinental Modelling and Assimilation Office (http://gmao.gsfc.nasa.gov ) are employed around the design, depending on a terrain-following sigma coordinate strategy with 30 vertical concentrations up to 0.01 hPa. Moreover, natural and anthropogenic emissions with no seasonal variation are included (Bey et al. 2001b ), introducing about 14% higher (lower) concentrations than the yearly mean in winter (summer) (Duncan and Bey, 2004 ).
Within this job, the tagging technique is applied inside design, considering 16 CO tracers (Table two ). In order to apply the nested-grid configuration, initially a 2-yr (2000, 2001) world-wide simulation (4°×5° grid-resolution) is performed. As 1-yr spin up is suggested, hourly boundary conditions (BCs) are saved available the nesting domain of Europe (20°W–45°E, 22°N–74°N) during the second run-year. The BCs are then carried out available the European domain for that nested-grid simulation (1°×1° grid-resolution).
Table two.  CO tagged tracers considered in GEOS-CHEM according to emission resources, geographical regions and chemical production
CO by methanol >>
two.two. Classification of circulation forms
With the existing study, an automated map pattern classification is developed following the methodology by Kostopoulou and Jones (2007 ). The obtained circulation catalogue describes the main seasonal circulation styles (CTs) over the NH at sea stage pressure (SLP) and at selected ranges (500 hPa, 200 hPa). Distinct synoptic patterns are produced over an extended European area, along with the atmospheric circulation is studied on the daily basis with the three atmospheric degrees. The ‘environment-to-circulation’ technique (Yarnal, 1993 ) is employed to study the influence of atmospheric circulation for the CO concentrations over Europe for 1 yr. The classification scheme serves as a software to offer the prevailing atmospheric circulation for each individual working day for the study 12 months in order to assess the CO concentrations as well as the LRT contribution over Europe. Towards this purpose, each individual representative working day of calendar year 2001 is assigned to just one of your derived synoptic circulation patterns, along with the simulated daily CO concentrations are grouped according to the prevailing CTs. Similarly, the regional as well as the LRT contributions to the European CO budget are calculated for each individual working day within the calendar year also, the success are interpreted in accordance with the prevailing CTs.
Table 3.  The main characteristics in the seasonal circulation patterns at SLP
Season of occurrence
Prevailing pressure methods in NH
Prevailing circulation over Europe
Location of main pressure centre over Europe
Icelandic Very low, Azores Higher, Siberian Superior
1. Fennoscandia, two. United Kingdom, 3. Central Europe–Western Mediterranean, four. Iberian Peninsula, 5. Central–Eastern Europe, 6. Benelux, 7. Eastern Mediterranean–Eastern Europe
Icelandic Affordable, Azores Very high, Siberian Large
1. Scandinavia, two. Iceland, 3. Central Mediterranean, four. Western Ireland–United Kingdom, 5. Central–Eastern Europe, 6. North Sea, 7. Eastern Mediterranean
Icelandic Affordable, Azores Significant, Siberian Large
1. Fennoscandia–North-eastern Europe, two. Central Europe–Central Mediterranean, 3. Ireland–United Kingdom, four. Iceland, 5. Central–Eastern Europe, 6. Iberian Peninsula, 7. Eastern Europe–Eastern Mediterranean, 8. Benelux
Icelandic Reduced, Azores Huge, Siberian Huge
1. Scandinavia, two. Central Europe–Central Mediterranean, 3. Ireland–United Kingdom, four. Iceland, 5. Eastern Europe, 6. Iberian Peninsula, 7. Eastern Mediterranean, 8.North Sea-Western Scandinavia
Azores Superior, Asian Thermal Very low
1. Fennoscandia, two. Central–Western Europe, 3. Ireland–United Kingdom, four. Iceland, 5. South-eastern Europe, 6. North Atlantic–Iberian Peninsula, 7. Central–Eastern Europe, 8. North Sea–Benelux
Azores Great, Asian Thermal Lower
1. Scandinavia, two. Central Europe, 3. United Kingdom, four. Iceland, 5. South-eastern Europe, 6. South-eastern Europe–Iberian Peninsula, 7. Eastern Europe, 8. Western Scandinavia
Icelandic Lower, Azores Great Siberian Superior
1. Scandinavia, two. Central Europe, 3. United Kingdom, four. Iceland, 5. Eastern Europe, 6. Iberian Peninsula, 7. Eastern Mediterranean–Eastern Europe, 8. Benelux
Icelandic Lower, Azores Excessive Siberian Great
1. Scandinavia, two. Central Mediterranean–Central Europe, 3. United Kingdom, four. Iceland, 5. Eastern Europe, 6. Iberian Peninsula, 7. Eastern Mediterranean, 8. Western Scandinavia
A great deal more specifically, gridded geopotential height reanalysis daily information in the three degrees from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR; Kalnay et al. 1996 ; Kistler et al. 2001 ) are applied as inputs to the synoptic map pattern classifications. The spatial coverage is two.5° in latitude by two.5° in longitude, providing a international grid of 144×73 points (90°N–90°S, 0°E–357.5°E). As this study emphasises within the prevailing NH circulation patterns by having a special interest over the European territory, 60-yr daily details from 1947 to 2007 are utilised for a region covering most with the NH (0°N–70°N, 90°W–90°E).
The for starters step towards the circulation classification is accomplished employing an eigenvector-based process. A rotated PCA (Wilks, 1995 ) is carried out (S-mode, making use of the correlation matrix), which lowers the variety in the original facts to some smaller selection of principal factors (PCs). Just about every PC incorporates a positive and also a negative phase both of those representing atmospheric classification modes. Correspondingly, 50 % of your circulation patterns are associated having a prominent anticyclonic centre (denoted by ‘+’) together with the remaining 50 % using a cyclonic centre (denoted by ‘−’), which govern the atmospheric conditions over the study region. Finally, every single working day in the original facts is assigned to a person mode according to the absolute maximum component scores. The methodology adopted to determine the map-pattern classification is described in greater depth in Kostopoulou and Jones (2007 ).
Table four.  Contribution (%) within the CO resources to the European CO concentrations at surface, 500 hPa and 200 hPa in winter and summer of 2001
two.3. Observations for your product evaluation
In this particular study, measurements of CO concentrations during 2001 from 31 rural background stations, located in Austria, France, Germany, Italy, Poland, Switzerland and also Netherlands (Fig. two a), are employed. Moreover, a PCA is applied with daily mean averages belonging to the CO-modelled concentrations from the 31 stations for your study calendar year, in order to classify the stations into groups with wide-spread characteristics. As a result, the original facts dimension is reduced into a smaller selection of PCs (Protonotariou et al. 2010 ). The PCA yielded three PCs (PC1, PC2, PC3), accounting for 80% within the total variance as suggested by the literature (Jolliffe, 1993 ). It is found that every PC component defines a sub-region (Fig. two b and Appendix S1 ) with very common characteristics in relation to emission intensity, topographical qualities and geographical position. Much more specifically, the 1st sub-region (PC1, capturing 33.7% for the total variance while in the original dataset) involves the stations located on the north-western part on the examined area. This station area, characterised by flat terrain and minimal altitudes, is close to effective anthropogenic resources. As a result, the mean emission rate is significantly very high (up to
50% higher than one other two sub-regions). Inside second sub-region (PC2, which explains 24.8% of your total variance), the stations are located inside southern part for the study region. This station area, located in a prolonged distance from the major anthropogenic resources, is characterised by complex topography along with a mean altitude of
400 m. The third sub-region (PC3, accounting for 22.6% within the total variance) comprises of stations located on the eastern part in the examined area, with lower background emissions in comparison to one other two groups and at similar mean altitude with PC2. For every single PC region, the LRT contribution is calculated on an yearly including a seasonal basis and therefore the circulation patterns that favour the transport paths are investigated.
Fig. 1 .   Intercontinental CO anthropogenic surface emissions (in molec/cm two /s). Black boxes depict the geographical regions considered in GEOS-CHEM tagged CO analysis; 1: Europe, two: North America, 3: Asia, four: Africa, 5: South America, 6: Oceania.
Fig. two .   a) European domain (http://www.ngdc.noaa.gov/mgg/topo/globegal.html#continents ) where the 31 rural background stations are located. b) PC1, PC2 and PC3 station regions in Europe.
Table 5.  Once-a-year contribution (%) of CO FFEU . CO FFNA . CO FFAS . CO FFRW and LRT (sum of CO FFNA . CO FFAS and CO FFRW ) to CO budget with the three station regions (PCs) in 2001
Statistical parameters for the observed (O) plus the estimated (ES) by the nested-grid simulation of GEOS-CHEM mean monthly CO concentrations in Europe are also presented. Statistical parameters equations tend to be found in Appendix S5 .
3. Good results and discussion
3.1. Circulation patterns’ analysis
In order to minimise the potential influences of seasonality and to give a detailed analysis belonging to the atmospheric circulation schemes in each individual season, the PCA in the circulation patterns is undertaken with a seasonal basis (Table 3 ). Fourteen CTs represent the atmospheric circulation at SLP over the NH in winter (December, January, February), declared by the acronym W_CTi (Winter Circulation Type, where i=±1,7 denotes the corresponding PC range). Sixteen CTs (i=±1,8) are associated with the main modes of atmospheric circulation in every of your next three seasons, which is, in spring (March, April, May, SP_CTi), summer (June, July, August, SU_CTi) and autumn (September, October, November, A_CTi). Correspondingly, 12 CTs are obtained that represent the atmospheric circulation at 500 hPa in winter (W 500 _CTi, i=±1,6) and autumn (A 500 _CTi, i=±1,6) and 16 in spring (SP 500 _CTi, i=±1,8) and summer (SU 500 _CTi, i=±1,8). Regarding the 200 hPa industry, 12 CTs are recognised because the dominant circulation patterns for winter and summer (W 200 _CTi and SU 200 _CTi; i=±1,6), and ten CTs for spring and autumn (SP 200 _CTi including a 200 _CTi; i=±1,5). A schematic representation from the main CTs on the three amounts is given in Appendix S2. The reliability of your classification is assessed by comparing the derived CT lessons with daily synoptic charts of atmospheric circulation (at SLP and then the two upper amounts), employing statistical analysis and visible comparison with NCAR/NCEP daily mean composites (http://www.esrl.noaa.gov/psd/data/composites/day/ ).
Table 6.  Percentage contribution (%) of CO FFNA . CO FFAS and their sum (CO FFLRT ) in winter at every PC sub-region in relation to the frequency of occurrence (FO) for the circulation patterns in percentage (%)
3.two. The CO budget at surface
The CO surface concentrations over Europe are mainly driven by the regional anthropogenic emissions, which contribute up to 79 and 68% to the European CO ranges at mid-latitudes in North Europe during winter and summer, respectively (Table four and Appendix S3, Fig. S3-1a, b, Appendix S4, Fig. S4-1 ). Furthermore, the CO accumulation close to the surface is related to the prevalence of frequent anticyclonic circulation patterns over Europe during the two seasons (e.g. W_CT1+, SU_CT7+, Fig. 3 a). Around the contrary, the CO FFEU contribution for the southern latitudes in winter does not exceed 35% (Fig. S4-1a ), because the regional emissions in South Europe are lower than those in Northern Europe. Moreover, the prevailing anticyclonic circulation patterns during the cold period (e.g. W_CT1+, W_CT2+, W_CT7+) do not favour transport from the highly polluted North European regions towards the south. However, the European contribution to Southern Europe increases during summer locally, mainly over sea, exceeding 40% (Fig. S4-1b ). These superior CO amounts are related with the transport on the pollutant from North to South Europe beneath the prevalence of regular summer CTs (e.g. SU_CT7±). The CO concentrations are lower over the land owing to the deep mixing height during this season.
Fig. 3 .   Frequency of occurrence of CTs in winter and summer of 2001 in a) SLP, b) 500 hPa, c) 200 hPa.
The CO production from the regional biomass burning is evident only during the warm period (not demonstrated), contributing up to 34 and 20% to the pollutant's local concentrations in Eastern and Southern Europe, respectively. Particularly in Greece, the prevailing northerly/northeasterly Etesian winds during summer favour the CO transport from the Northern and Eastern Europe underneath the prevalence of representative summer flow patterns (e.g. SU_CT7+). Through this transport path enhanced CO concentrations from the burning of agricultural residences in Eastern Europe ended up transported towards Greece in August 2001 (Lelieveld et al. 2002 ; Balis et al. 2003 ; Salisbury et al. 2003 ; Tombrou et al. 2009 ).
The impact on the North American anthropogenic emissions to the European surface CO concentrations is a little more profound in winter (Fig. S4-2a ). The CO FFNA contribution is higher for the western part from the European continent involving 35°N and 45°N (up to 18%), where air masses are channelled underneath the prevalence of most anticyclonic and cyclonic patterns during this season (W_CT1−, W_CT2−, W_CT3+, W_CT4+, W_CT5±, W_CT6±, W_CT7±). Many of these patterns (W_CT4+, W_CT5−, W_CT6±) also favour CO FFNA to be transported towards the Mediterranean region. In summer (Fig. S4-2b ), the CO FFNA contribution is weaker (up to
12%), attributed to the lower anthropogenic emissions in North America during this season. Moreover, the less organised atmospheric circulation in summer does not favour this transport path. In particular, the LRT takes destination mainly towards the northern/northwestern parts of Europe, as being the westerly winds over the North Atlantic turn to southwesterly for most in the summer CTs (e.g. SU_CT7+). In the other hand, the largest contribution of your Asian anthropogenic tracer is apparent about the eastern borders from the European domain in winter (34%, Fig. S4-3a ) since the prevailing circulation patterns (e.g. W_CT1+) do not favour the intrusion further into the European continent. The CO FFAS contribution can be pronounced on the western/south-western parts of Europe in winter (up to
20%) and inside of the Eastern Mediterranean in summer (up to
15%), attributed to the westerly circulation along with the extension in the Asian thermal Affordable over the Aegean Sea, respectively. The North American as well as the Asian biomass burning contributions are found up to 5% (not proven), due to minimal fire activity in 2001 (EC, 2002 ; Kasischke et al. 2005 ; Yurganov et al. 2005 ; Huang et al. 2009 ). The contribution for the anthropogenic resources from the rest in the world to the European CO surface concentrations is negligible (not demonstrated), mainly considering that the northeastly Trade winds along with the ITCZ prevent the air intrusion from the Southern Hemisphere (SH) into the NH. Similarly, although the fire intensity around the SH contributes significantly to the world CO budget (Table 1 ), this sort of signals are not transmitted towards Europe. Very smallish contributions for the North African anthropogenic and biomass burning emissions (up to 5%) are observed in winter (not proven), if the atmospheric conditions favour this transport path (e.g. W_CT6+).
The methane oxidation is the largest chemical production operation of CO. The highest contribution is found for the southern regions where the solar radiation is intense, reaching 22 and 32% in winter and summer, respectively (not demonstrated). Moreover, CO CH4 is enhanced on the excessive northern latitudes in summer, attributed to the increased CH four production during the permanent ice-covered regions during this season. Among the NMVOCs, the isoprene oxidation contributes the highest CO concentrations (up to 18% for the densely vegetated eastern parts of Europe in summer), as it consists over 40% of their total emissions (Miyoshi et al. 1994 ; Paulot et al. 2009 ). Similarly, the CO production by other NMVOCs (monoterpenes, methanol, acetone) is highest in summer (up to eleven, 6 and 2%, respectively), attributed to the huge temperatures and also increased solar radiation that enhance the photochemical activity during this season.
Table 7.  Percentage contribution (%) of CO FFNA . CO FFAS and their sum (CO FFLRT ) in spring at each and every PC sub-region in relation to the frequency of occurrence (FO) with the circulation patterns in percentage (%)
3.3. The CO budget at rural background stations in Europe
In order to further investigate the LRT contribution to the European CO concentrations at SLP, a a good deal more detailed examination is performed influenced by the PC analysis. To this aim, the once-a-year LRT contribution from every single continent's anthropogenic emissions (CO FFNA . CO FFAS and CO FFRW ) too as their total sum is presented with the three PC station regions, together with the regional (CO FFEU ) contribution (Table 5. Fig. four ). On an yearly basis, the LRT contributions to the three PC regions are found comparable. A slightly higher contribution is evident in PC2 and PC3, partly attributed to the fact that these sub-regions, which are characterised by relatively lower regional emissions, locate at large altitudes, where the LRT contribution increases. Moreover, a statistical analysis is likewise presented with the three PC regions. It is found that the product adequately simulates the observations in any respect regions. The most beneficial effectiveness is achieved in PC1 (Mean Observation, M O =217.8 ppbv; Mean Bias, MB=−four.1 ppbv; Mean Error, ME=32.9 ppbv; correlation coefficient, R two =0.83), attributed to the fact that this region is characterised by flat terrain, which is effectively depicted by the product. The largest bias and error are found in PC2 (M O =208.four ppbv, MB=−28.0 ppbv, ME=49.1 ppbv, R two =0.57 ppbv), as being the representation for the complex topography from the model's coarse grid is probably not sufficient.
Fig. four .   Time series with the mean daily concentrations of CO measurements (black squares) and modelled concentrations of CO total (red line) and CO FFEU (green line) inside left axis and LRT (sum of CO FFNA . CO FFAS and CO FFRW . purple line) concentrations with the right axis in 2001 in a) PC1, b) PC2, c) PC3.
In order to define the atmospheric conditions that favour the LRT towards the study regions, the analysis is extended over a seasonal basis. To this aim, the contribution with the anthropogenic emissions with the major continental resources (North America and Asia) to the total CO concentration, in addition as their sum (CO FFLRT ), is calculated in percentage (<CO>x /CO total ] *100, where x=CO FFNA or CO FFAS ) at every PC region. This analysis is performed in relation to the prevailing circulation patterns with a seasonal basis, together with their frequency of occurrence during the study yr (Tables 6 –9 ). Moreover, in order to assess how perfectly the source contributions are linked to the CTs, the standard deviation with the North American and Asian contributions continues to be calculated for all CTs (not revealed). It should be noted that the circulation patterns depict the general characteristics on the atmospheric circulation and they do not represent the real wind direction and velocity (or pressure values), which in turn determine the source contribution to the study area. Therefore, it is expected that there will be some variability inside the effects. In most cases nevertheless, it was found that the LRT contribution is satisfactorily linked with most belonging to the circulation patterns, with the standard deviation inside the source contributions estimated amongst four and eleven.8% belonging to the contribution itself.
Table 9.  Percentage contribution (%) of CO FFNA . CO FFAS and their sum (CO FFLRT ) in autumn at each individual PC sub-region in relation to the frequency of occurrence (FO) from the circulation patterns in percentage (%)
3.3.1. Winter.
The LRT contribution in the surface CO concentrations with the three PC regions during winter reaches
30%, with the Asian contribution (18.1%) being higher than the North American contribution (12.8%) less than all CTs (Table 6 ). The highest CO FFLRT contribution is found in PC3 (29.6%) beneath the prevalence of your cyclonic pattern W_CT5−. This CT with relatively reduced frequency of occurrence in 2001 (FO: 5.6%, Table 6 ) is associated with the extension from the Azores Substantial over the Western Mediterranean together with the formation of the deep decreased eastwards to PC3. Underneath these conditions, the southwesterly winds over the North Atlantic turn southeastwards before arriving to the study area. Similarly, the LRT contribution in PC1 is highest (28.6%) underneath the prevalence within the same cyclonic pattern, exceeding up to
10% the regional contribution on some days (Fig. four a). As Table 6 shows, the LRT towards PC1 and PC3 is most intensive mainly when cyclonic circulation prevails over Europe during winter. However, it should be mentioned that enhanced LRT contribution (28.1%) also can occur underneath the prevalence from the less frequent anticyclonic type W_CT4+ (FO: two.2%), formed if the well-organised Azores Large extends northeastwards, reaching the study regions.
The highest LRT contribution in PC2 (27.7%) is observed beneath the prevalence belonging to the cyclonic circulation type W_CT2−. This relatively frequent pattern (FO: 8.9%) is associated with westerly winds over the North Atlantic that channel the air masses towards the study area. This flow is established in the event the well-organised deep Icelandic Reduced additionally, the Azores Substantial are formed northwestwards and southwestwards of PC2, respectively. Underneath the prevalence of this circulation pattern, the LRT contribution in PC2 can exceed by up to 21.8% the regional one particular (Fig. four b). Moreover, the LRT contribution exceeds the regional just one by up to 45.9% underneath the cyclonic pattern W_CT4−, when a deep decreased develops westwards of PC2. Below these conditions, winds over the North Atlantic shift from northwesterly to southwesterly before arriving to the study area.
3.3.two. Spring.
The CO FFLRT contribution in spring (31.1%) is for the same amount as in winter. Similarly to winter, the Asian contribution (19.2%) is higher in comparison to the North American (13.5%) for all CTs (Table 7 ). In particular, the highest LRT contribution is accumulated in PC2 underneath the prevalence from the anticyclonic pattern SP_CT6+. This less frequent CT in 2001 (FO: two.2%) is associated with the formation in the deep Azores Excessive southwestwards of PC2. Less than these conditions, the prevailing southwesterly winds over the North Atlantic turn to northwesterlies before arriving with the PC2 region. With this case, the CO FFLRT contribution can exceed the CO FFEU contribution by up to 36% (Fig. four b). Moreover, the LRT contribution are usually up to
45% higher than the regional a person underneath the prevalence for the added frequent cyclonic patterns SP_CT1−, SP_CT3− and SP_CT4− (FO: 6.5, 15.two and 6.5%, respectively). Underneath these conditions, the deep Icelandic Affordable and also the Azores Higher are formed north/northwestwards and southwestwards of PC2 respectively, inducing westerly winds towards the study area.
The largest LRT accumulation in PC1 (27.8%) and PC3 (twenty five.4%) takes spot underneath the prevalence from the cyclonic patterns SP_CT2− (FO: 7.6%) and SP_CT7− (FO: 1.1%). These CTs are related with the formation of the small pressure centre over the Mediterranean, which combined with the great pressures westwards of PC1 and PC3, induces northerly and southwesterly winds, respectively, towards these areas. Moreover, it is noticed that the CO FFLRT contribution in PC3 exceeds by up to 14.6% the CO FFEU amounts (Fig. four c) underneath the prevalence of SP_CT4+ (FO: 15.2%) and SP_CT6− (FO: 12%).
3.3.3. Summer.
The LRT contribution in summer (up to 22.1%) is lower than in winter and spring. During this case, the Asian contribution (12.9%) is higher in comparison to the North American contribution (ten.4%) for most CTs (Table 8 ). The largest contribution is observed in PC1 underneath the prevalence of your anticyclonic pattern SU_CT3+. This relatively frequent type (FO: 7.6%) is associated with the extension in the deep Azores Superior over Western Europe, steering the southwesterly winds over the North Atlantic southeastwards before arriving to the area. Below these atmospheric conditions, the LRT contribution in PC1 and PC2 can exceed the regional an individual (up to 8 and 16.8%, respectively, Fig. four a, b). Similarly, the highest contribution in PC3 (19.2%) is observed beneath the same anticyclonic pattern. Enhanced LRT contributions in PC3 (18.3%) and PC1 (21%) are also observed underneath the cyclonic patterns SU_CT1− and SU_CT8− respectively. Moreover, the highest LRT contribution in PC2 (20.6%) is found underneath the latter CT. Less than these conditions, the formation of the minimal pressure centre to the north plus a large pressure model inside of the North Atlantic induces northwesterly winds towards the study area. A contribution of
20% is likewise observed in PC2 underneath the anticyclonic patterns SU_CT3+ and SU_CT4+.
3.3.four. Autumn.
The LRT contribution in autumn is evidently lower than in winter and spring (and slightly lower than in summer). Moreover, contrary to the opposite seasons, the North American contribution is higher in comparison to the Asian for most CTs (Table 9 ). The highest LRT (19.9%) and CO FFNA contributions (ten.9%) are found in PC1 underneath A_CT1− (FO: 8.8%). This cyclonic pattern is associated with the formation of the deep cyclonic centre over Scandinavia, extending northwards over the study area. The mixture of this procedure with the excessive pressure southwards establishes westerly winds towards PC1. Enhanced LRT contribution (19.6%) is in addition observed in PC1 underneath the highly frequent anticyclonic pattern A_CT3+ (FO: 19.8%). Similarly, the highest LRT contribution in PC3 (18.6%) occurs beneath the same anticyclonic and cyclonic patterns.
The highest LRT contribution in PC2 (18.8%) is found beneath the A_CT5+ (FO: 7.7%). This anticyclonic circulation pattern is associated using an extended well-organised very high pressure strategy over Europe. Furthermore, the LRT contribution in PC2 becomes important (up to 17.8%) beneath the additional frequent A_CT7+ and A_CT8− patterns (FO: 11%). Only number of LRT exceedances are observed in autumn 2001, with CO FFLRT being higher by up to 5.4% than CO FFEU (Fig. four b) mainly underneath the prevalence of A_CT1− and A_CT8−.
3.four. The CO budget with the costless troposphere (MT and UT)
The CO concentrations for the upper stages over Europe are significantly lower than those over the surface, decreasing by up to
70% over highly polluted regions (Fig. S3-1c to f ). The CO stages with the MT during winter (Fig. S1-1c ) increase from south (up to
110 ppbv) to north (up to
130 ppbv). This latitudinal distribution is attributed to the longer CO photochemical lifetime (due to the lower solar radiation) and to your considerably more intense LRT beneath the prevalence of frequent winter CTs (e.g. W 500 _CT1±, Fig. 3 b). The computed summer stages are in general lower than
100 ppbv (Fig. S3-1d ). However, higher concentrations are calculated in Eastern Europe due to robust convection. This well-known upward flow over this region (Duncan and Bey, 2004 ) is usually evident from some of the most frequent summer CTs at SLP (Fig. 3 a). The CO concentrations at 200 hPa are in general lower than 100 ppbv, except over Eastern Europe where they may possibly be supported by the convective mixing (Fig. S3-1e, f ).
The chemical production is the major source of CO with the cost-free troposphere (not revealed), exceeding 50% within the UT during summer (Table four ). Moreover, the LRT inside of the MT/UT is considerably more profound than inside LT. The largest contribution originates from Asia, reaching 25% in Western Europe and at higher latitudes in winter (Fig. S6-3a, c ). This distribution reflects the transport paths followed by the pollutant beneath the influence on the prevailing winter CTs from the MT (e.g. W 500 _CT1±, Fig. 3 b) and UT (W 200 _CT5±, Fig. 3 c). In summer, CO FFAS from the MT/UT (Fig. S6-3b, d ) is in general lower than in winter. However, higher contributions are observed from the UT over the Eastern Mediterranean (
30%), when a ridge extends over the greater area (e.g. SU 200 _CT1+). These conditions cultivate easterly winds that transfer CO FFAS towards the Eastern Mediterranean and North Africa. The North American contribution is higher at significant latitudes inside of the MT during winter (up to 18%, Fig. S6-2a ). Moreover, the CO FFNA contribution around the UT reaches 14% over the Iberian Peninsula as well as the Western Mediterranean during summer (Fig. S6-2d ). This distribution is favoured by the westerly/southwesterly circulation that's established underneath the influence in the prevailing CTs at these heights (e.g. SU 500 _CT3−, SU 500 _CT5−, SU 200 _CT1+, SU 200 _CT2+). The anthropogenic and biomass burning emissions signals from Africa are detected only in the southern parts (up to 6%, not demonstrated) when a ridge over the Mediterranean Sea and North Africa transfers the air masses towards Southern Europe (W 200 _CT3+, W 200 _CT5+). Over the contrary, the impact belonging to the regional anthropogenic resources decreases significantly, contributing up to 18 and 10% inside of the MT together with the UT during winter, respectively (Fig. S6-1 ). However, as now mentioned, there are some regions over Eastern Europe, where CO FFEU reaches 22% on the UT due to robust convection in summer.
Similarly to the surface, some differences are found in between GEOS-CHEM and MOZART-2 benefits at 500 hPa and 200 hPa. Moreover, the contribution from the anthropogenic emissions (additionally, the chemistry production) in GEOS-CHEM is up to
20% higher (lower) than MATCH-MPIC effects over Western Europe in MT (Fischer et al. 2006 ). These discrepancies are attributed to the intercontinental models’ configurations (i.e. grid resolution, emission inventories, OH concentrations).
four. Conclusions
While in the existing study, the European CO budget was examined in relation to the prevailing atmospheric conditions in 2001, according to the nested-grid simulations for the GEOS-CHEM intercontinental design. To this aim, a seasonal CT classification was developed to the NH with the SLP and two atmospheric amounts within the MT additionally, the UT, over a 60-yr period. It was found that the regional anthropogenic emissions have significant impacts around the European CO degrees during the LT, contributing to the surface CO budget up to
80%, based upon the season plus the atmospheric conditions. Particularly in winter, the anticyclonic circulation patterns over Europe favoured the pollutant's accumulation close to the resources. In summer, the prevailing northerly winds favoured the pollutant's transport of anthropogenic or biomass burning origins from Northern and Eastern Europe southwards, increasing the CO stages in Southern Europe.
The transport in the anthropogenic pollution from North America and Asia towards the European LT was favoured by the westerly circulation, contributing up to 18–20% each individual to the CO surface concentrations over Europe in winter. To the contrary, the less organised atmospheric circulation in summer, in conjunction with the lower anthropogenic emissions, constrained these contributions to 12–15% during this season. The Asian along with the North American contributions at three regions in Europe, where CO measurements had been available in the market at 31 rural background stations with the study calendar year, had been found highest (lowest) in winter and spring (summer and autumn). In winter, the LRT at SLP was intense mainly underneath the prevalence of cyclonic circulation patterns. During another seasons, the pollutant's transport towards Europe was enhanced for several cyclonic and anticyclonic patterns. The Asian tracer contribution was found higher than the North American in winter, spring and summer less than most CTs (but lower in autumn). Events where the LRT contribution is higher than the regional a person by up to
45% had been detected in any respect station sites mainly in winter and spring. The LRT contribution increased around the no cost troposphere, with the Asian anthropogenic sources’ contribution being higher than the North American in most cases. In particular, the Asian tracer reached
30% over the Eastern Mediterranean within the UT during summer, favoured by the prevailing easterlies. Around the MT, this contribution was 25% during winter in Western Europe and at higher latitudes, reflecting the transport pathways followed by the pollutant beneath the influence from the prevailing winds. Similarly, the North American contribution was highest during winter (summer) from the MT (UT) in the western parts belonging to the continent, reaching 18% (14%). To the other hand, no significant amount of CO originated from the remaining parts from the world. Reduced biomass burning signals from Africa have been detected over Southern Europe within the UT (6%). The regional anthropogenic emissions’ contribution with the 100 percent free troposphere was lower than the surface, contributing 18% (10%) during the MT (UT). However, higher regional contribution was found over Eastern Europe in summer (22%) due to robust convection. The contribution on the CO chemical production was superior in the slightest degree stages and seasons, exceeding 50% while in the UT during summer. Quantitative differences concerning GEOS-CHEM and other world-wide models’ outcome were being attributed mainly to different models’ configurations.
5. Acknowledgments
Datasets were being provided by the NOAA/ESRL Physical Sciences Division, Boulder, Colorado, from their Net page http://www.esrl.noaa.gov/psd/data/composites/day/. We also acknowledge European Environmental Agency (© E.E.A, Copenhagen, 2001) for providing Airbase details.
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About The Authors
Anna P. Protonotariou University of Athens, Department of Physics, Division of Environmental Physics and Meteorology Greece
Effie Kostopoulou University with the Aegean, Department of Geography, University Hill, Mytilene GR 81100, Greece Greece
Maria Tombrou University of Athens, Department of Physics, Division of Environmental Physics and Meteorology Greece
Christos Giannakopoulos Institute for Environmental Research and Sustainable Growth, National Observatory of Athens, V.Pavlou and Metaxa Str. GR-15236 Palaia Pendeli, Athens, Greece. Greece
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