1. Topic

  How to locate monitoring stations?

2. Introduction

   

The location of the monitoring stations in an urban monitoring network is an important issue. There are two basic applications of urban air quality monitoring data which sets, to some extent different, requirements to the location of the stations:

· Assessment of air quality directly from the monitoring results, as a basis for evaluation of exposure and health (and other) effects and

· Use of the monitoring for evaluation of dispersion models.

In both cases, the proper locating of stations is important, following certain criteria.

Some requirements to monitoring station location are given in the EU AQ Daughter Directives. Specifications of types of monitoring stations, with some location criteria, are given as part of the EU Exchange of Information (EoI) Decision as well as in EEA EUROAIRNET Criteria report (see references and links below).

Locating monitoring stations is an integral part of the Design of urban air quality monitoring network, which is described in topic How to design Urban monitoring networks, and what methods to use ?.

3. Discussion

   

Stations used for direct assessment of urban air quality

The number and types of stations to be established in the urban area is part of the network design process (see topic: How to design Urban monitoring networks, and what methods to use ?).

It has then also been decided in which parts of the urban area the stations will be located. This part of the location process can be termed "macro-locating", a term also referred to in the Directives, with some guidance.

The actual detailed locating of the station within the given area is then termed "micro-locating".

Important considerations re. micro-locating:

· The location must be representative of a certain area around it, so its measurements won't be representing only the very small area where it is located. The EoI Guidance report as well as the Directives and the EUROAIRNET criteria report give guidance of the minimum requirements on area of representativeness.

· The location of the air intake (or probe) relative to nearly dominating sources. See EoI and the Directives for guidance and

· The intake (or probe) for air to be sampled by the instruments must be placed according to given criteria, so that the sampled air is not influenced unduly by very local effects (such as distance to walls, vegetation, etc.)

Problems with micro-locating typically arises regarding availability of space for a station cabin at the desired location, and availability of electric power, phone lines (not so important now as mobile phones can be used), security and easy access. Such problems may result in compromises between the ideal and possible locations to be chosen.

An important aspect of the representativeness of a station location, in addition to its representativeness area, is its representativeness for the exposure situations it is supposed to represent: How does the station represent similar areas of exposure in the city? A good assessment of the representativeness area would require special monitoring and modelling studies. The need for such studies must be evaluated in each case.

Stations used for evaluation of dispersion models

In addition to the above criteria and problems, the locating of stations for model testing has to fulfil the following criteria:

Its location must be representative of an area which corresponds to the spatial resolution of the dispersion model. For instance.

· For a grid model which gives a calculated value which represents the average of e.g. a 1 km2 area, the station must be located such that it also represents the average concentration of the km2 area around it, which corresponds with the actual location of the grid used in the model. The model also represents the concentration in a certain height, or rather, the average value (height wise) of a layer of air of a given height (e.g. the lowest 30 m of the atmosphere). The combination of the location and height of the air inlet for the instruments must also be chosen so as to represent a similar average value, height wise.

· For a subgrid model, e.g. a line source model which calculates the concentrations near streets/roads, the station location must reflect the situation which is represented by the model. Typically, such a model gives the concentrations for an idealised type of street/building configuration (e.g. continuous building facades of similar height, both sides, although Computational Fluid Dynamics (CFD) models exist which can calculate concentrations for more complex configurations) along the street section, away from influence from complicating effects near intersections. Typically, such stations should be located away from intersections in street sections with fairly homogeneous building topography.

4. Recommendation / Conclusion

   

The detailed location of AQ monitoring stations is a process that follows the network design process (see the How to design Urban monitoring networks, and what methods to use ?). Prepare for the station location by studying the EoI guidance, the Directives and the EUROAIRNET texts. Look also at examples from other cities, which have been through the process to benefit from their experiences.

5. Examples / Further Reading

   

Monitoring locations in Turku region

The Influence of Sampling Height to concentration of air pollutants

The Veneto Region air quality monitoring network optimisation project

Further Examples:

Example of monitoring networks in Bristol
An Urban Monitoring Network in Birmingham, UK
Biological monitoring of air quality: Example used in the surroundings of the Porto Marghera industrial area (Venice, I)
Study of atmospheric depositions in the surroundings of the porto Margera industrial area (Venice, I) and in corresponence with some biomonitoring stations.

6. Additional Documents / Web Links

   

· EU AQ Directives, especially Annexes related to locating of stations: http://europa.eu.int/comm/environment/air/ambient.htm

· Guidance on AQ Assessment under the AQ Directives report: http://europa.eu.int/comm/environment/air/pdf/guidanceunderairquality.pdf

· EEA EUROAIRNET Criteria Report: http://reports.eea.eu.int/search_results?SearchTitle=euroairnet

· Exchange of Information (EoI) Decision and its Guidance report: http://europa.eu.int/comm/environment/air/pdf/guidancetoannexes97101ec.pdf

Last Updated


 

25th January 2005

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