1. Topic

2. Introduction

There can be various objectives behind the assessment of the air quality in urban areas and there is a variety of methods used in the assessment leading to different levels of usefulness of the results.

The methodology of urban air quality assessment (AQA) is influenced by its objectives, which can be policy-related and/or research-related. Policy-related objectives are: the comparison between ambient air pollution levels assessed in zones/agglomerations and the limit values (LVs), to quantify the exceedances; the development of cost-effective action plans to reduce air pollutants levels; the evaluation of the effectiveness of policy measures (including future projections and scenarios); the information to the public.

Research-related objectives are: providing data for health/other effects (on the vegetation and cultural heritage) studies, to implement new AQA tools (such as geo-statistical techniques, dispersion modelling, etc.).

In this topic the main emphasis is to describe structure and methods of urban air quality (AQ) Assessments with basis in the requirements set in the EU AQ Directives. The further emphasis will be on how various methods fulfil AQ assessment objectives and on the applicability and usefulness of the results from the various methods.

One of the basic requirements of the Framework Directive (http://www.europa.eu.int/comm/environment/air/index.htm) is that EU Member States make AQA in their territory, using methodologies depending upon the ambient air quality levels seen relative to the AQ limit values. The process is as follows:

· A preliminary AQA is carried out for the whole territory to assess preliminary the AQ levels in the various cities/agglomerations, as well as in rural areas, relative to the limit values.

· Based on this, each Member State divides its territory into “air quality zones”, including agglomerations (urban areas with more than 250,000 inhabitants) that are suitable for assessment and management.

· In the zones, different AQA regimes come into effect dependent upon the air pollution levels (see Topic Terms in the EC Air Quality Directives: What do they mean?)

· Monitoring networks and modelling capabilities are established in the zones according to set requirements in the Daughter Directives.

· Periodical AQ assessments are then carried out, and the results reported to the Commission regularly.

· Plans and programmes for improvements in the air quality are then mandated in the zones where the limit values are exceeded (see e.g. Topic How to develop an Air Quality Action Plan ?).

The different basic “methods” of air quality assessment are:

· Monitoring of air quality levels, by means of stationary stations, mobile laboratories and diffusive sampling techniques;

· Modelling of pollutants’ concentrations and depositions;

· Combination of monitoring and modelling, called “data assimilation”, meaning that the model’s predictions can be improved when combining it with monitoring data.

In the Member States the Authority responsible to make AQA can be different (regional/national, province/county, urban/local), depending on the transposition of AQ Directives (AQD) into the national legislation. At local or urban level, the methodology adopted to perform Air Quality Assessment (AQA) depends on the level of air pollution (LV, UAT, LAT, see below) registered in the zone or agglomeration comprising the urban area and on its objectives. Sometimes the “quality” of urban AQA is affected by human, technical and economic limitations, so that only a basic level of AQA can be performed.

3. Discussion

AQA methods

The following overview (the table and figure below) shows the different AQ “assessment regimes”, how the AQA methods are related to the requirements in the Framework Directive (FWD) and how they fulfil various assessment objectives:

APC: air pollutant concentration; LV: Pollutant Limit Value; UAT and LAT: Upper and Lower Assessment Threshold.

The word “low quality” in the table means methods which are simple and often less expensive, and having less accuracy, rather than implying poor quality as such.

Further description of AQA methodologies in light of the requirements of the European Commission is given in a technical guidance report to the AQ Directives:

http://www.europa.eu.int/comm/environment/air/pdf/guidanceunderairquality.pdf

Assessment by monitoring

Both traditionally, and as required by the Directives, monitoring is the first “method” to use in AQ assessments, in urban areas as on other scales. The differentiation in the Directives between high, medium and low level quality (read: “accuracy”) monitoring reflects the experience and practices acquired by the air pollution monitoring community over several decades.

· “Low quality” monitoring methods, to be used both in the preliminary assessment phase, and later when it has been demonstrated that the pollution level is low, include e.g. passive samplers, simple manual samplers taking daily average samples, etc. (see e.g. Preliminary Assessment methods report: http://reports.eea.eu.int/TEC11a/en ).

· High quality” monitoring methods, which are required in agglomerations and when the air pollution concentration exceeds UAT, entail automatic monitors giving hourly values or better, with near real time transfer of data, so information to the public can be given. The methods must comply with the accuracy requirements in the Directives.

· “Medium quality monitoring”, which is to be used when the air pollution concentration is between UAT and LAT, does not imply that there are some separate “medium quality” types of methods. It means rather that fewer locations may need to be monitored, and the intensity of monitoring can be less, for instance covering less of the time of the day/week/year, mobile monitoring stations can be used to a larger extent, etc.

Monitoring methods present some important topics, such as: the optimisation of the macro-sitting or network design, as well as micro-sitting parameters; stationary monitoring stations’ classification (e.g.: urban background station, traffic hot-spot station, etc.); sampling and analysis of polluted air at a particular location, including calibration techniques (reference methods, equivalent methods, Quality Control/Quality Assessment); indicative measurements such as the use of mobile laboratories and the diffusive sampling techniques; estimation of the human/economic resources needed to maintain the network’s efficiency. (See the topic descriptions in the section Air Quality Monitoring Methods.)

General references on AQ monitoring methods: see Additional Documents section below.

Assessment by modelling

Use of modelling methods is suggested under the new AQ Directives, to assess the spatial distribution of concentrations (such as iso-lines in maps) and the analysis of the causes of air pollution (by means of the emission inventories), which have to be reported for zones/agglomerations where levels exceed limit values.

Advancing from monitoring to modelling involves some important steps: the implementation of an emission inventory (see the Topic How to develop urban Emission Inventories?) and the set up of monitoring of meteorological and dispersion data, and dispersion and/or statistical. This is a major step for local authorities, in terms of additional expertise and capacity. Often the tasks involving modelling are contracted out to expert consultants.

Relevant items for modelling methods are: the type of model and its choice, which is depending on the application to be implemented; its input data requirements (meteorological data or modelling and the emission inventory); the topography of the area; the monitoring data needed for the model’s validation; using monitoring data to improve the local applicability of the model; the needed results, deriving from the various model runs, for example: evaluation of present Air Quality status; contributions from selected human/natural activities or single sources (e.g. industrial point sources, emissions from harbour’s activities, etc.); distribution of population exposure (e.g. patterns of exposure due to traffic emissions, or to industrial emissions in the nearby of an urban area); future Air Quality projections, to evaluate effectiveness of policies.

General references on AQ modelling and models:

· http://reports.eea.eu.int/92-9167-028-6/en/tab_abstract_RLR

· http://www.epa.gov/scram001

· http://www.arb.ca.gov/html/aqe&m.htm

· http://air-climate.eionet.eu.int/databases/MDS/index_html

· http://www.harmo.org/

· http://www.uwe.ac.uk/aqm/centre/model.html

· http://www.europa.eu.int/comm/environment/air/cafe/activities/activities.htm

· Note by the CAFE-Working Group on Implementation, Nr. 2003/3, Subject: “Air Quality assessment around point sources”): Air Quality assessment around point sources (pdf 20K)

4. Recommendation / Conclusion

The initial identification of the levels of pollution (Preliminary AQA) is a fundamental step to determine what the requirements for assessment in the individual zones are, as given in the AQ Directives. (See the Guidance Report on Preliminary Assessment under EC Air Quality Directives, web-link below). After that, the “quality” of the following AQA depends on human, technical and economic resources available to the experts in the field of air quality assessment within governmental or local authorities, and their capacity to out-source various assessment tasks. Technical Guidance is given by the EU to choose the most suitable method to perform it (see web-links below). The performance of AQA can be regarded as a gradual process that can be improved in parallel with the acquirement of more sophisticated tools and techniques to assess air quality (i.e. statistical and mathematical modelling). However, local authorities have the responsibility to perform assessments according to the requirements in the AQ Directives.

5. Examples / Further Reading

Traffic, Emissions and AQ Models in HEAVEN integrated AQMS system in Rome

Further Examples:

6. Additional Documents / Web Links

Background references on AQA structure/methods:

· Framework Directive 96/62/EC, Daughter Directives 1999/30/EC, 2000/69/EC and 2002/3/EC: http://www.europa.eu.int/comm/environment/air/index.htm;

· Guidance report on preliminary assessment under EC air quality directives: http://reports.eea.eu.int/TEC11a/en;

· Overview of Methods and Results of the Preliminary Assessment of Air Quality in Europe under Directives 96/62/EC and 1999/30/EC:http://www.europa.eu.int/comm/environment/air/pdf/reportpreliminaryasses.pdf

· Technical guidance on how to assess air quality under the new EU air quality directives, in particular the Framework Directive 96/62/EC and the first Daughter Directive 1999/30/EC (with examples):http://www.europa.eu.int/comm/environment/air/pdf/guidanceunderairquality.pdf

· World Bank, Urban air quality management strategy in Asia - guidebook: http://www-wds.worldbank.org/servlet/WDS_IBank_Servlet?stype=AllWords&all=urbair&ptype=sSrch&pcont=results&sortby=D&sortcat=D&x=13&y=10;

· UK 2003 Guidance for Air Quality Management (Policy Guidance LAQM.PG(03) and Technical Guidance LAQM.TG(03)): http://www.uwe.ac.uk/aqm/centre/

Background references related to AQA by monitoring methods

· US EPA Ambient AQ Monitoring Information Centre: http://www.epa.gov/ttn/amtic/

· Jon Bower: Ambient Air Quality Monitoring. In Air Quality management, Issues in Environmental Science and Technology, Monograph 8 (Eds: R.E. Hester and R.M. Harrison); The Royal Society of Chemistry. Herts, UK.

· Monitoring Ambient Air Quality for Health Impact Assessment; WHO Regional Publications, European Series, No. 85.

· Criteria for EUROAIRNET - The EEA Air Quality Monitoring and Information Network, Technical report No 12: http://reports.eea.eu.int/TEC12/en/tab_content_RLR;

· Exchange of Information (EoI) Decision and Guidance note:

· Council Decision 97/101/EC.

· Commision Decision 2001/752/EC

· Guidance report on the Annexes to Decision 97/101/EC (pdf 930K)

· http://europa.eu.int/comm/environment/air/cafe/pdf/working_groups/01121718guidanceoverview.pdf and http://europa.eu.int/comm/environment/air/cafe/pdf/steering_technical_group/item6_eolreview.pdf;

· CEN standards: http://www.cenorm.be/catweb/cwsen.htm

Background references on modelling methods

· European Topic Centre on Air and Climate Change, Topic Centre of European Environment Agency, Model Documentation System (MDS): http://air-climate.eionet.eu.int/databases/mds.html;

· EUROTRAC 2: GENEMIS Project: http://www.ier.uni-stuttgart.de/public/de/organisation/abt/tfu/projekte/genemis/

Examples of assessment from monitoring, European scale

· European scale: European Environmental Agency, Air Quality in Europe Reports 1999, 2000: Air quality in Europe: state and trends 1990-99

· Air pollution in Europe 1990-2000

· European Topic Centre on Air and Climate Change, Topic Centre of European Environment Agency, European Air Quality in 1998, Final Report: http://air-climate.eionet.eu.int/reports/EoI_European_Air_Quality_In_1998_FinalReport

Examples of assessment from modelling

Regional/National scale: EMEP (Convention on Long-Range Transboundary Air Pollution): http://www.emep.int/ and RAINS: http://www.iiasa.ac.at/rains/Rains-online.html?sb=8

Last Updated

25th January 2005