<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!DOCTYPE article SYSTEM "http://www.atmos-chem-phys.net/inc/acp/copernicus.dtd">
<article language="en">
	<journal>
		<journal_title>Atmospheric Chemistry and Physics</journal_title>
		<journal_url>www.atmos-chem-phys.net</journal_url>
		<issn>1680-7316</issn>
		<eissn>1680-7324</eissn>
		<volume_number>9</volume_number>
		<issue_number>8</issue_number>
		<publication_year>2009</publication_year>
	</journal>
	<doi>10.5194/acp-9-2695-2009</doi>
	<article_url>http://www.atmos-chem-phys.net/9/2695/2009/</article_url>
	<abstract_html>http://www.atmos-chem-phys.net/9/2695/2009/acp-9-2695-2009.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys.net/9/2695/2009/acp-9-2695-2009.pdf</fulltext_pdf>
	<start_page>2695</start_page>
	<end_page>2714</end_page>
	<publication_date>2009-04-23</publication_date>
	<article_title content_type="html">The impact of weather and atmospheric circulation on O&lt;sub&gt;3&lt;/sub&gt; and PM&lt;sub&gt;10&lt;/sub&gt; levels at a rural mid-latitude site</article_title>
	<authors>
		<author numeration="1" affiliations="1,2">
			<name>M. Demuzere</name>
			<email>matthias.demuzere@ees.kuleuven.be</email>
		</author>
		<author numeration="2" affiliations="2">
			<name>R. M. Trigo</name>
		</author>
		<author numeration="3" affiliations="3">
			<name>J. Vila-Guerau de Arellano</name>
		</author>
		<author numeration="4" affiliations="1">
			<name>N. P. M. van Lipzig</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Earth and environmental Sciences, Celestijnenlaan 200E, 3001 Heverlee (Leuven), Katholieke Universiteit Leuven, Belgium</affiliation>
		<affiliation numeration="2" content_type="html">Centro de Geofísica da Universidade de Lisboa (CGUL), IDL, University of Lisbon, Fac. Ciencias, Campo Grande, Ed. C8, Piso 6, 1749-016 Lisbon, Portugal</affiliation>
		<affiliation numeration="3" content_type="html">Meteorology and Air Quality Section, Wageningen University, Droevendaalsesteeg 4, P.O. Box 47, 6700 AA Wageningen, The Netherlands</affiliation>
	</affiliations>
	<abstract content_type="html">In spite of the strict EU regulations, concentrations of surface ozone and
PM&lt;sub&gt;10&lt;/sub&gt; often exceed the pollution standards for the Netherlands and
Europe. Their concentrations are controlled by (precursor) emissions, social
and economic developments and a complex combination of meteorological
actors. This study tackles the latter, and provides insight in the
meteorological processes that play a role in O&lt;sub&gt;3&lt;/sub&gt; and PM&lt;sub&gt;10&lt;/sub&gt; levels in
rural mid-latitudes sites in the Netherlands. The relations between
meteorological actors and air quality are studied on a local scale based on
observations from four rural sites and are determined by a comprehensive
correlation analysis and a multiple regression (MLR) analysis in 2 modes,
with and without air quality variables as predictors. Furthermore, the
objective Lamb Weather Type approach is used to assess the influence of the
large-scale circulation on air quality. Keeping in mind its future use in
downscaling future climate scenarios for air quality purposes, special
emphasis is given to an appropriate selection of the regressor variables
readily available from operational meteorological forecasts or AOGCMs
(Atmosphere-Ocean coupled General Circulation Models). The regression models
perform satisfactory, especially for O&lt;sub&gt;3&lt;/sub&gt;, with an (&lt;i&gt;R&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt; of 57.0%
and 25.0% for PM&lt;sub&gt;10&lt;/sub&gt;. Including previous day air quality information
increases significantly the models performance by 15% (O&lt;sub&gt;3&lt;/sub&gt;) and
18% (PM&lt;sub&gt;10&lt;/sub&gt;). The Lamb weather types show a seasonal distinct pattern
for high (low) episodes of average O&lt;sub&gt;3&lt;/sub&gt; and PM&lt;sub&gt;10&lt;/sub&gt; concentrations, and
these are clear related with the meteorology-air quality correlation
analysis. Although using a circulation type approach can provide important
additional physical relations forward, our analysis reveals the circulation
method is limited in terms of short-term air quality forecast for both
O&lt;sub&gt;3&lt;/sub&gt; and PM&lt;sub&gt;10&lt;/sub&gt; (&lt;i&gt;R&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt; between 0.12 and 23%). In summary, it is
concluded that the use of a regression model is more promising for
short-term downscaling from climate scenarios than the use of a weather type
classification approach.</abstract>
	<references>
		<reference numeration="1" content_type="text"> Agirre-Basurko, E., Ibarra-Berastegi, G., and Madariaga, I.: Regression and multilayer perceptron-based models to forecast hourly O&lt;sub&gt;3&lt;/sub&gt; and NO&lt;sub&gt;2&lt;/sub&gt; levels in the Bilbao area, Environ. Model. Softw., 21, 430–446, 2006. </reference>
		<reference numeration="2" content_type="text"> Ainslie, B. and Steyn, D. G.: Spatiotemporal trends in episodic ozone pollution in the Lower Fraser Valley, British Columbia, in relation to mesoscale atmospheric circulation patterns and emissions, J. Appl. Meteor. Climatol., 46, 1631–1644, 2007. </reference>
		<reference numeration="3" content_type="text"> Al-Alawi, S. M., Abdul-Wahab, S. A., and Bakheit, C. S.: Combining principal component regression and artificial neural networks for more accurate predictions of ground-level ozone, Environ. Model. Softw., 23, 396–403, 2008. </reference>
		<reference numeration="4" content_type="text"> Andersson, C. and Langner, J.: Inter-anual variations of ozone and nitrogen dioxide over europe during 1958–2003 simulated with a regional CTM, Water Air Soil Poll., 7, 15–23, 2007a. </reference>
		<reference numeration="5" content_type="text"> Andersson, C., Langner, J., and Bergström, R.: Interannual variation and trends in air pollution over Europe due to climate variability during 1958–2001 simulated with a regional CTM coupled to the ERA40 reanalysis, Tellus A, 59B, 77–98, 2007b. </reference>
		<reference numeration="6" content_type="text"> Barrero, M. A., Grimalt, J. O., and Canton, L.: Prediction of daily ozone concentration maxima in the urban atmosphere, Chemometr. Intel. Lab. Sys., 80, 67–76, 2006. </reference>
		<reference numeration="7" content_type="text"> Baur, F., Hess, P., and H. Nagel, H.: Kalendar der Groswetterlagen Europas 1881–1939, Bad Homburg, Germany, 1944. </reference>
		<reference numeration="8" content_type="text"> Beljaars, A. C. M. and Bosveld, F. C.: Cabauw data for the validation of land surface parameterization schemes, J. Clim., 10, 1172–1193, 1997. </reference>
		<reference numeration="9" content_type="text"> Benvenuto, F. and Marani, A.: Nowcasting of urban air pollutants by neural networks, Nuovo Cimento Della Societa Italiana Di Fisica C-Geophysics and Space Physics, 23, 567–586, 2000. </reference>
		<reference numeration="10" content_type="text"> Bridgeman, H. and O&apos;Connor, J.: Relationships between air pollution and meteorology in Newcastle, Australia, Proceedings of the 6th international conference on Urban Air Quality, 2007. </reference>
		<reference numeration="11" content_type="text"> Brunekreef, B. and Holgate, S. T.: Air pollution and health, Lancet 360, 1233–1242, 2002. </reference>
		<reference numeration="12" content_type="text"> Cannon, A. J., Whitfield, P. H., and Lord, E. R.: Synoptic map-pattern classification using recursive partitioning and principal component analysis, Mon. Weather Rev., 130, 1187–1206, 2002. </reference>
		<reference numeration="13" content_type="text"> Cheng, S. Q. and Lam, K. C.; Synoptic typing and its application to the assessment of climatic impact on concentrations of sulfur dioxide and nitrogen oxides in Hong Kong, Atmos. Environ., 34, 585–594, 2000. </reference>
		<reference numeration="14" content_type="text"> Cobourn, W. G., Dolcine, L., French, M., and Hubbard, M. C.: A comparison of nonlinear regression and neural network models for ground-level ozone forecasting, J. Air Waste Manage. Assoc., 50, 1999–2009, 2000. </reference>
		<reference numeration="15" content_type="text"> Cobourn, W. G.: Accuracy and reliability of an automated air quality forecast system for ozone in seven Kentucky metropolitan areas, Atmos. Environ.t, 41, 5863–5875, 2007. </reference>
		<reference numeration="16" content_type="text"> Comrie, A. C.: An enhanced synoptic climatology of ozone using a sequencing technique, Phys. Geogr., 13, 53–65, 1992. </reference>
		<reference numeration="17" content_type="text"> Comrie, A. C. and Yarnal, B.: Relationships between Synoptic-Scale Atmospheric Circulation and Ozone Concentrations in Metropolitan Pittsburgh, Pennsylvania, Atmos. Environ., 26, 301–312, 1992. </reference>
		<reference numeration="18" content_type="text"> Comrie, A. C.: Comparing neural networks and regression models for ozone forecasting, J. Air Waste Manage. Assoc., 47, 653–663, 1997. </reference>
		<reference numeration="19" content_type="text"> D&apos;Andrea, F., Tibaldi, S., Blackburn, M., Boer, G., Deque, M., Dix, M. R., Dugas, B., Ferranti, L., Iwasaki, T., Kitoh, A., Pope, V., Randall, D., Roeckner, E., Straus, D., Stern, W., Van den Dool, H., and Williamson, D.: Northern Hemisphere atmospheric blocking as simulated by 15 atmospheric general circulation models in the period 1979–1988, Clim. Dynam., 14, 385–407, 1998. </reference>
		<reference numeration="20" content_type="text"> Davies, T. D., Kelly, P. M., Low, P. S., and Pierce, C. E.: Surface Ozone Concentrations in Europe – Links with the Regional-Scale Atmospheric Circulation, J. Geophys. Res.-Atmos., 97, 9819–9832, 1992a. </reference>
		<reference numeration="21" content_type="text"> Davies, T. D., Farmer, G., Kelly, P. M., Glover, G. M., Apsimon, H. M., and Barthelmie, R. J.: Surface Pressure Pattern Indicators of Mean Monthly Pollutant Concentrations in Southern Scandinavian Precipitation - a Test Using Case-Studies of Months with High and Low Concentrations of Nonmarine Sulfate and Nitrate, Atmos. Environ., 26, 261–278, 1992b. </reference>
		<reference numeration="22" content_type="text"> Davis, J. M. and Speckman, P.: A model for predicting maximum and 8 h average ozone in Houston, Atmos. Environ., 33, 2487–2500, 1999. </reference>
		<reference numeration="23" content_type="text"> de Arellano, Jordi Vila-Guerau, Duynkerke, P. G., Jonker, P. J., and Builtjes, P. J. H.: An observational study on the effects of time and space averaging in photochemical models, Atmos. Environ., 27, 353–362, 1993. </reference>
		<reference numeration="24" content_type="text"> Delcloo, A. W. and De Backer, H.: Modelling planetary boundary layer ozone, using meteorological parameters at Uccle and Payerne, Atmos. Environ., 39, 5067–5077, 2005. </reference>
		<reference numeration="25" content_type="text"> Delcloo, A. W. and De Backer, H.: Five day 3D back trajectory clusters and trends analysis of the Uccle ozone sounding time series in the lower troposphere (1969–2001), Atmos. Environ., 42, 4419–4432, 2008. </reference>
		<reference numeration="26" content_type="text"> Demuzere, M., Werner, M., Van Lipzig, N. P. M, and Roeckner, E.: An analysis of present and future ECHAM5 pressure fields using a classification of circulation patterns, Int. J. Climattol., 28(1), 1–15, doi:10.1002/joc.1821, 2008. </reference>
		<reference numeration="27" content_type="text"> European Union: Council Directive 1999/39/EC of 22 April 1999 regulating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air, Official Journal of the European Communities, L163, 0041–0060, 1999. </reference>
		<reference numeration="28" content_type="text"> European Union: Directive 2008/50/EC of the European Parliament and of the council of 21 May 2008 on ambient air quality and cleaner air for Europe. Official Journal of the European Union L 152/1, 2008. </reference>
		<reference numeration="29" content_type="text"> Flemming, J., Stern, R., and Yamartino, R. J.: A new air quality regime classification scheme for O&lt;sub&gt;3&lt;/sub&gt;, NO&lt;sub&gt;2&lt;/sub&gt;, SO&lt;sub&gt;2&lt;/sub&gt; and PM$_10$ observations sites, Atmos. Environ., 39, 6121–6129, 2005. </reference>
		<reference numeration="30" content_type="text"> Gardner, M. W. and Dorling, S. R.: Artificial neural networks (the multilayer perceptron) – A review of applications in the atmospheric sciences, Atmos. Environ., 32, 2627–2636, 1998. </reference>
		<reference numeration="31" content_type="text"> Gardner, M. W. and Dorling, S. R.: Neural network modelling and prediction of hourly NOx and NO2 concentrations in urban air in London, Atmos. Environ., 33, 709–719, 1999. </reference>
		<reference numeration="32" content_type="text"> Gardner, M. W. and Dorling, S. R.: Meteorologically adjusted trends in UK daily maximum surface ozone concentrations, Atmos. Environ., 34, 171–176, 2000. </reference>
		<reference numeration="33" content_type="text"> Giorgi, F. and Meleux, F.: Modelling the regional effects of climate change on air quality, Comp. Rend. Geosci., 339, 721–733, 2007. </reference>
		<reference numeration="34" content_type="text"> Goyal, P., Chan, A. T., and Jaiswal, N.: Statistical models for the prediction of respirable suspended particulate matter in urban cities, Atmos. Environ., 40, 2068–2077, 2006. </reference>
		<reference numeration="35" content_type="text"> Graedel, T. E. and Crutzen, P. J.: Atmospheric Change: An Earth System Prospective, Freeman, New York, USA, 1993. </reference>
		<reference numeration="36" content_type="text"> Grivas, G. and Chaloulakou, A.: Artificial neural network models for prediction of PM$_10$ hourly concentrations, in the Greater Area of Athens, Greece, Atmos. Environ., 40, 1216–1229, 2006. </reference>
		<reference numeration="37" content_type="text"> Guicherit, R. and Van Dop, H.: Photochemical production of ozone in western Europe (1971–1975) and its relation to meteorology, Atmos. Environ., 11, 145–155, 1977. </reference>
		<reference numeration="38" content_type="text"> Harrison, R. M., Deacon, A. R., Jones, M. R., and Appleby, R. S.: Sources and processes affecting concentrations of PM$_10$ and PM$_2.5$ particulate matter in Birmingham (UK), Atmos. Environ., 31, 4103–4117, 1997. </reference>
		<reference numeration="39" content_type="text"> Hess, P. and Brezowsky, H.: Katalog der Großwetterlagen Europas. Ber. Dt. Wetterd. in der US-Zone 33, Bad Kissingen, Germany, 1952. </reference>
		<reference numeration="40" content_type="text"> Hooyberghs, J., Mensink, C., Dumont, G., Fierens, F., and Brasseur, O.: A neural network forecast for daily average PM$_10$ concentrations in Belgium, Atmos. Environ., 39, 3279–3289, 2005. </reference>
		<reference numeration="41" content_type="text"> Hubbard, M. C. and Cobourn, W. G.: Development of a regression model to forecast ground-level ozone concentration in Louisville, KY, Atmos. Environ., 32, 2637–2647, 1998. </reference>
		<reference numeration="42" content_type="text"> Huth, R., Beck, C., Philipp, A. Demuzere, M. Ustrnul, Z., Cahynová, M., Kysel\&apos;y, K., and Tveito, O. E.: Classifications of atmospheric circulation patterns: recent advances and applications, Annals of the New York Academy of sciences, 1146, 105–152, 2008. </reference>
		<reference numeration="43" content_type="text"> Intergovernmental Panel on Climate Change (IPCC): the Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the IPCC 2007, available online at: http://www.ipcc.ch, 2007. </reference>
		<reference numeration="44" content_type="text"> Jacobson, M. Z.: On the causal link between carbon dioxide and air pollution mortality, Geophys. Res. Lett., 35(3), 1–5, 2008. </reference>
		<reference numeration="45" content_type="text"> Jenkinson, A. F. and Collison, B. P.: An initial climatology of gales of the North Sea, Synoptic climatology Branch Memorandum, 62, 1977. </reference>
		<reference numeration="46" content_type="text"> Jol, A. and Kielland, G. (Eds.): Air Pollution in Europe 1997, European Environment Agency, Copenhagen, Denmark, 1997. </reference>
		<reference numeration="47" content_type="text"> Jones, P. D., Hulme, M., and Briffa, K. R.: A Comparison of Lamb Circulation Types with an Objective Classification Scheme, Int. J. Climatol., 13, 655–663, 1993. </reference>
		<reference numeration="48" content_type="text"> Jones, P. D., Hulme, M., and Briffa, K. R.: A Comparison of Lamb Circulation Types with an Objective Classification Scheme, Int. J. Climatol., 13, 655–663, 1993. </reference>
		<reference numeration="49" content_type="text"> Kalkstein, L. S. and Corrigan, P.: A Synoptic Climatological Approach For Geographical Analysis: Assessment of Sulfur Dioxide Concentrations, Ann. Assoc. Am. Geogr., 76, 381–395, 1986. </reference>
		<reference numeration="50" content_type="text"> Kalkstein, L. S., Nichols, M. C., Barthel, C. D., and Greene, J. S.: A new spatial synoptic classification: Application to air-mass analysis, Int. J. Climatol., 16, 983–1004, 1996. </reference>
		<reference numeration="51" content_type="text"> Kassomenos, P. A., Sindosi, O. A., Lolis, C. J., and Chaloulakou, A.: On the relation between seasonal synoptic circulation types and spatial air quality characteristics in Athens, Greece, J. Air Waste Manage. Assoc., 53, 309–324, 2003. </reference>
		<reference numeration="52" content_type="text"> Kruskal, H. and Wallis, W. A.: Use of ranks in one-criterion variance analysis, J. Am. Stat. Assoc., 47, 583–621, 1952. </reference>
		<reference numeration="53" content_type="text"> Kukkonen, J., Partanen, L., Karppinen, A., Ruuskanen, J., Junninen, H., Kolehmainen, M., Niska, H., Dorling, S., Chatterton, T., Foxall, R., and Cawley, G.: Extensive evaluation of neural network models for the prediction of NO&lt;sub&gt;2&lt;/sub&gt; and PM$_10$ concentrations, compared with a deterministic modelling system and measurements in central Helsinki, Atmos. Environ., 37, 4539–4550, 2003. </reference>
		<reference numeration="54" content_type="text"> Lasry, F., Coll, I., and Buisson, E.: An insight into the formation of severe ozone episodes: modeling the 21/03/01 event in the ESCOMPTE region, Atmos. Res., 74, 191–215, 2005. </reference>
		<reference numeration="55" content_type="text"> Lu, H. C., Hsieh, J. C., and Chang, T. S.: Prediction of daily maximum ozone concentrations from meteorological conditions using a two-stage neural network, Atmos. Res., 81, 124–139, 2006. </reference>
		<reference numeration="56" content_type="text"> Medina, S., Plasencia, A., Ballester, F., Mucke, H. G., Schwartz, J.: Apheis: public health impact of PM$_10$ in 19 European cities, J. Epidem. Comm. Health, 58, 831–836, 2004. </reference>
		<reference numeration="57" content_type="text"> Mondal, R., Sen, G. K., Chatterjee, M., Sen, B. K., and Sen, S.: Ground-level concentration of nitrogen oxides (NO&lt;sub&gt;x&lt;/sub&gt;) at some traffic intersection points in Calcutta, Atmos. Environ., 34, 629–633, 2000. </reference>
		<reference numeration="58" content_type="text"> Norusis, M. J.: SPSS 11.0 guide to data analysis, Upper saddle River, NJ, Prentice Hall, 2002. </reference>
		<reference numeration="59" content_type="text"> NRC: Human exposure assessment for airborne pollution: advances and opportunities, National Acadamy Press, Washington DC, USA, 321 pp., 1991. </reference>
		<reference numeration="60" content_type="text"> Murphy, A. H.: Skill scores based on the mean square error and their relationship to the correlation coefficient, Mon. Weather Rev., 116, 2417–2424, 1988. </reference>
		<reference numeration="61" content_type="text"> Nunnari, G., Nucifora, A. F. M., and Randieri, C.: The application of neural techniques to the modelling of time-series of atmospheric pollution data, Ecol. Model., 111, 187–205, 1998. </reference>
		<reference numeration="62" content_type="text"> Oanh, N. T. K., Chutimon, P., Ekbordin, W., and Supat, W.: Meteorological pattern classification and application for forecasting air pollution episode potential in a mountain-valley area, Atmos. Environ., 39, 1211–1225, 2005. </reference>
		<reference numeration="63" content_type="text"> Papanastasiou, D. K., Melas, D., and Kioutsioukis, I.: Development and assessment of neural network and multiple regression models in order to predict PM$_10$ levels in a medium-sized mediterranean city, Water Air Soil Poll., 182, 325–334, 2007. </reference>
		<reference numeration="64" content_type="text"> Perez, P., Trier, A., and Reyes, J.: Prediction of PM2.5 concentrations several hours in advance using neural networks in Santiago, Chile, Atmos. Environ., 34, 1189–1196, 2000. </reference>
		<reference numeration="65" content_type="text"> Perez, P.: Prediction of sulfur dioxide concentrations at a site near downtown Santiago, Chile, Atmos. Environ., 35, 4929–4935, 2001. </reference>
		<reference numeration="66" content_type="text"> Reich, S. L., Gomez, D. R., and Dawidowski, L. E.: Artificial neural network for the identification of unknown air pollution sources, Atmos. Environ., 33, 3045–3052, 1999. </reference>
		<reference numeration="67" content_type="text"> Reis, S., Simpson, D., Friedrich, R., Jonson, J. E., Unger, S., and Obermeier, A.: Road traffic emissions - predictions of future contributions to regional ozone levels in Europe, Atmos. Environ., 34, 4701–4710, 2000. </reference>
		<reference numeration="68" content_type="text"> Santer, B. D., Wigley, T. M. L., Boyle, J. S., Gaffen, D. J., Hnilo, J. J., Nychka, D., Parker, D. E., and Taylor, K. E.: Statistical significance of trends and trend differences in layer-average atmospheric temperature time series, J. Geophys. Res.-Atmos., 105, 7337–7356, 2000. </reference>
		<reference numeration="69" content_type="text"> Satsangi, G. S., Lakhani, A., Kulshrestha, P. R., and Taneja, A.: Seasonal and diurnal variation of surface ozone and a preliminary analysis of exceedance of its critical levels at a semi-arid site in India, J. Atmos. Chem., 47, 271–286, 2004. </reference>
		<reference numeration="70" content_type="text"> Schaap, M., Apituley, A.,~Timmermans, R M A., Koelemeijer, R B A and~de~Leeuw, G.: Exploring the relation between aerosol optical depth and PM$_2.5$ at Cabauw, the Netherlands, Atmos. Chem. Phys., 9, 909–925, 2009. </reference>
		<reference numeration="71" content_type="text"> Schlink, U., Herbarth, O., Richter, M., Dorling, S., Nunnari, G., Cawley, G., and Pelikan, E.: Statistical models to assess the health effects and to forecast ground-level ozone, Environ. Model. Softw., 21, 547–558, 2006. </reference>
		<reference numeration="72" content_type="text"> Seinfeld, J. H. and Pandis, S. N.: Atmospheric chemistry and physics from air pollution to climate change, New York, John Wiley &amp; Sons, Inc, 1113 pp., 1998. </reference>
		<reference numeration="73" content_type="text"> Semazzi, F.: Air quality research: perspective from climate change modelling research, Environ. Int., 29, 253–261, 2003. </reference>
		<reference numeration="74" content_type="text"> Sillman, S.: The relation between ozone, NOx and hydrocarbons in urban and polluted rural environments, Atmos. Environ., 33, 1821–1845, 1999. </reference>
		<reference numeration="75" content_type="text"> Sillman, S. and He, D. Y.: Some theoretical results concerning O&lt;sub&gt;3&lt;/sub&gt;-NO&lt;sub&gt;x&lt;/sub&gt;-VOC chemistry and NO&lt;sub&gt;x&lt;/sub&gt;-VOC indicators, J. Geophys. Res.-Atmos., 107, 26–41, 2002. </reference>
		<reference numeration="76" content_type="text"> Smith, R. L., Davis, J. M., Sacks, J., Speckman, P., and Styer, P.: Regression models for air pollution and daily mortality: analysis of data from Birmingham, Alabama, Environmetrics, 11, 719–743, 2000. </reference>
		<reference numeration="77" content_type="text"> Slini, T., Kaprara, A., Karatzas, K., and Moussiopoulos, N.: PM$_10$ forecasting for Thessaloniki, Greece, Environ. Model. Softw., 21, 559–565, 2006. </reference>
		<reference numeration="78" content_type="text"> Stadlober, E., Hormann, S., and Pfeiler, B.: Quality and performance of a PM$_10$ daily forecasting model, Atmos. Environ., 42, 1098–1109, 2008. </reference>
		<reference numeration="79" content_type="text"> Styer, P., Mcmillan, N., Gao, F., Davis, J., and Sacks, J.: Effect of Outdoor Airborne Particulate Matter on Daily Death Counts, Environ. Health Perspect., 103, 490–497, 1995. </reference>
		<reference numeration="80" content_type="text"> Sousa, S. I. V., Martins, F. G., Alvim-Ferraz, M. C. M., and Pereira, M. C.: Multiple linear regression and artificial neural networks based on principal components to predict ozone concentrations, Environmental Modelling &amp; Software 22, 97–103, 2007. </reference>
		<reference numeration="81" content_type="text"> Trigo, R. M. and DaCamara, C. C.: Circulation weather types and their influence on the precipitation regime in Portugal, Int. J. Climatol., 20, 1559–1581, 2000. </reference>
		<reference numeration="82" content_type="text"> Trigo, R. M., Trigo, I. F., DaCamara, C. C., and Osborn, T. J.: Climate impact of the European winter blocking episodes from the NCEP/NCAR Reanalyses, Clim. Dynam., 23, 17–28, 2004. </reference>
		<reference numeration="83" content_type="text"> Tulet, P., Crassier, V., and Rosset, R.: Air pollution modelling at a regional scale, Environ. Model. Softw., 15, 693–701, 2000. </reference>
		<reference numeration="84" content_type="text"> van der Wal, J. T. and Janssen, L. H. J. M.: Analysis of spatial and temporal variations of PM$_10$ concentrations in the Netherlands using Kalman filtering, Atmos. Environ., 34, 3675–3687, 2000. </reference>
		<reference numeration="85" content_type="text"> Warneck P.: Chemistry of the Natural Atmosphere, 2nd ed., International Geophysics Series Vol.71, Academic Press, New York, USA, 1998. </reference>
		<reference numeration="86" content_type="text"> Wilks, D. S.: Statistical Methods in the Atmospheric Sciences, Academic Press, San Diego, CA, USA, 476 pp., 1995. </reference>
		<reference numeration="87" content_type="text"> Wise, E. K. and Comrie, A. C.: Meteorologically adjusted urban air quality trends in the Southwestern United States, Atmos. Environ., 39, 2969–2980, 2005. </reference>
		<reference numeration="88" content_type="text"> WHO: Air quality guidelines for Europe, 2nd ed. Copenhagen, World Health Organization Regional Office for Europe, 2000 (WHO Regional Publications, European Series No. 91), 2000. </reference>
		<reference numeration="89" content_type="text"> WHO: World Health Organisation air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide, global update 2005, Summary of risk assessment, World Health Organization Regional Office for Europe, 2005. </reference>
		<reference numeration="90" content_type="text"> Yarnal, B.: Synoptic climatology in environmental analysis, London, Belhaven Press, 195 pp., 1993. </reference>
		<reference numeration="91" content_type="text"> Ziomas, I. C., Melas, D., Zerefos, C. S., Bais, A. F., and Paliatsos, A. G.: Forecasting peak pollutant levels from meteorological variables, Atmos. Environ., 29, 3703–3711, 1995. </reference>
	</references>
</article>

