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Meteorology applied to urban air pollution problems:concepts from COST 715
B. Fisher, J. Kukkonen, M. Piringer, M. W. Rotach, M. Schatzmann
To cite this version:B. Fisher, J. Kukkonen, M. Piringer, M. W. Rotach, M. Schatzmann. Meteorology applied to urbanair pollution problems: concepts from COST 715. Atmospheric Chemistry and Physics, EuropeanGeosciences Union, 2006, 6 (2), pp.555-564.
Atmos. Chem. Phys., 6, 555564, 2006www.atmos-chem-phys.net/6/555/2006/ Author(s) 2006. This work is licensedunder a Creative Commons License.
Meteorology applied to urban air pollution problems: concepts fromCOST 715
B. Fisher1, J. Kukkonen2, M. Piringer3, M. W. Rotach4, and M. Schatzmann5
1Environment Agency, Kings Meadow House, Reading RG1 8DQ, UK2Finnish Meteorological Institute, Air Quality Research, Sahaajankatu 20 E, 00 880 Helsinki, Finland3Central Institute for Meteorology and Geodynamics, Hohe Warte 38, 1190 Vienna, Austria4Swiss Federal Office for Meteorology and Climatology, MeteoSwiss, Kraebuehlstrasse 58, Zurich 8044, Switzerland5University of Hamburg Meteorological Institute, Bundesstrasse 55, 20 146 Hamburg, Germany
Received: 13 July 2005 Published in Atmos. Chem. Phys. Discuss.: 31 August 2005Revised: 21 November 2005 Accepted: 11 January 2006 Published: 22 February 2006
Abstract. The outcome of COST 715 is reviewed from theviewpoint of a potential user who is required to consider ur-ban meteorology within an air pollution assessment. It isshown that descriptive concepts are helpful for understand-ing the complex structure of the urban boundary layer, butthat they only apply under a limited number of conditions.However such concepts are necessary to gain insight intoboth simple and complex air pollution models. It is arguedthat wider considerations are needed when considering rou-tine air quality assessments involving an air quality modelsformulation and pedigree. Moreover there appears to be areluctance from model developers to move away from famil-iar concepts of the atmospheric boundary layer even if theyare not appropriate to urban areas. An example is given fromCOST 715 as to how routine urban meteorological measure-ments of wind speed may be used and adapted for air qualityassessments. Reference to the full COST 715 study is madewhich provides further details.
This paper is a selective review of the COST 715 pro-gramme Meteorology applied to Urban Air Pollution Prob-lems which ran between 19982004. COST is a Europeanactivity which supports scientific exchange and networks. Inurban areas as anywhere else wind, turbulence profiles, sur-face heat flux and mixing height are required to run air qual-ity pollution transport models, including both simple disper-sion models and more complex, numerical simulation mod-els (Middleton, 2002).
Correspondence to: B. Fisher([email protected])
Meteorological pre-processing models provide the bound-ary conditions, or parameter values, profiles etc., needed bythe pollution transport models. Such boundary conditionsand parameter values and profiles are commonly supplied forrural areas. The purpose of COST 715 is to give informationabout methods for providing this meteorological informationfor urban pollution transport models. The urban situation isimportant, as pollution levels are generally highest in urbanareas. In COST 715 a large number of methods have been re-viewed. Notable results are the need to describe properly theroughness sub-layer of the atmosphere, containing and in thevicinity of large urban roughness elements, to treat the urbansurface heat exchange at night, and to interpret large urbanfield programmes and urban air pollution episodes. In addi-tion COST 715 provides advice on where urban meteorolog-ical data may be obtained. It suggests a so-called referenceheight for urban meteorological wind speed measurements.The final report of the project provides further details of theresults (Fisher et al., 2005).
2 Urban complexity and the NUSAP method of evalu-ating models
The main feature of the urban boundary layer is its complex-ity. One can no longer assume that the atmospheric boundarylayer is homogeneous. As seen from Fig. 1, the urban bound-ary layer involves wide variations in time and space scales.However at the same time decision makers require predic-tions relating to important issues concerning air quality andhuman health. In addition, some of the meteorological vari-ables needed for urban air quality assessments are quanti-ties that are not routinely measured, such as the surface fluxparameters or the mixing layer depth. This paper considers
Published by Copernicus GmbH on behalf of the European Geosciences Union.
556 B. Fisher et al.: Meteorology applied to urban air pollution problems
Fig. 1. Schematic diagram showing processes, flow and scale lengths within an urban boundary layer, UBL. This is set in the context ofthe planetary boundary layer, PBL, the urban canopy layer, UCL, and the sky view factor, SVF, a measure of the degree to which the sky isobscured by surrounding buildings at a given point which characterises the geometry of the urban canopy.
the framework for dealing with complexity, and the parallelquestion of uncertainty, within the urban atmospheric bound-ary layer. It will mainly deal with simple approaches in con-trast to advanced methods. Other papers in this Special Issueof Atmospheric Chemistry and Physics, on Urban Meteorol-ogy and Atmospheric Pollution (EMS-FUMAPEX), discussadvanced models.
Modelling approaches leading to predictions and decisionshave been subject to review within the so-called NUSAPframework. In this approach it is argued (Ravetz and Funtow-icz, 20061) that model results should be structured to containnumbers, units, spread, assessment and pedigree. The first
1Ravetz, J. R. and Funtowicz, S. O.: The management of un-certainty and quality in quantitative information, http://www.nusap.net, 2006.
three are familiar to the conventional atmospheric modellerbeing concerned with the predictions and the uncertaintyassociated with predictions, though with some of the mostcomplex models it is not possible to predict all aspects of pa-rameter variations. This is why in the research project Inte-grated Systems for Forecasting Urban Meteorology, Air Pol-lution and Population Exposure (FUMAPEX, project web-site: http://fumapex.dmi.dk/, see this Special Issue) a rangeof models are used to introduce a spread in results.
The need for an assessment of models and consideration oftheir pedigree is less familiar. Assessment refers to qualita-tive judgement regarding the value of a model description. Inthis paper models of features of the urban boundary layer aredescribed in figures, showing the characteristics of the urbanflow. The modeller tries to capture these within his model.
Atmos. Chem. Phys., 6, 555564, 2006 www.atmos-chem-phys.net/6/555/2006/
B. Fisher et al.: Meteorology applied to urban air pollution problems 557
Fig. 2. Interaction of the rural boundary layer as it impacts on to the urban area showing the development of an internal boundary layerat a transition to a rougher surface z02z01: (a) after Hunt and Simpson, (b) after Melas and Kambezidis. The change in the potentialtemperature profile and the surface potential temperatures s1 and s2 are also shown, illustrating the development of the thermal internalboundary layer, TIBL.
However one cannot assume that by including these featuresone will necessarily obtain better predictions. An importantaspect of assessment is that a model should be accessible andis not treated as a black box. Simple models are an effectiveway within modelling to obtain insight into how a model per-forms. This is why it may be advantageous to use a range oftechniques in parallel e.g. numerical models, physical mod-els and field experiments. Pedigree refers to the applicationof the model. A model with a good pedigree is often referredto as one which is well established.
Assessment and pedigree also need to consider the contextin which the model is used. For urban meteorology the mostimportant decisions will apply to the Air Quality FrameworkDirective and to planning decisions relating to new devel-opment in a city (such as the expansion of an airport) oradding new housing to extend a city. One needs a suitabledescription of the meteorology in relation to the other mainfactors, such as emissions and the description of dispersionand chemical reactions, which affect air quality (Karppinenet al., 2000a, b). Since models are usually ultimately testedagainst measurements, it is not easy to tell what would bethe errors arising from an incorrect treatment of meteorology.For the Air Quality Directive, exceedences of the long-termaverages of PM10 and NO2 are of major interest for whichquite approximate methods may be adequate. However thereis also interest in episodes of high pollution, which can onlybe adequately covered by the application of c