Air quality: Monitoring and reporting

Ambient air monitoring is the systematic, long-term assessment of pollutant levels by measuring the quantity and types of certain pollutants in the surrounding, outdoor air.

Currently, in developed countries, ambient air quality is monitored using networks of strategically located sensors. In most cases, high-quality reference-grade instruments are used to ensure data integrity and allow regulation and compliance monitoring. However, lower-cost sensors are becoming more widely accepted and used. This is especially the case in developing countries, such as Africa, where “hybrid” air quality monitoring networks have been developed that combine low-cost sensors and reference-grade instruments. Ambient air monitoring is an integral part of an effective air quality management system.

The main reasons to collect such data include to:

• assess the extent of and composition of pollution
• provide air pollution data to the general public during disasters and emergencies
• support the implementation of air quality goals or standards
• evaluate the effectiveness of emissions control strategies
• provide information on air quality trends
• provide data for the evaluation of air quality models
• support research (eg long-term studies of the health effects of air pollution).

There are different methods to measure any given pollutant. A developer of a monitoring strategy examines the options to determine which methods are most appropriate, taking into account the main uses of the data, initial investment costs for equipment, operating costs, reliability of systems, and ease of operation.

The locations of monitoring stations depend on the purpose of the monitoring. Most air quality monitoring networks are designed to support human health objectives, and monitoring stations are established in population centres. They may be near busy roads, in city centres, or at locations of particular concern (eg a school, hospital, or near particular emissions sources). Monitoring stations also may be established to determine background air pollution levels, away from urban areas and emission sources.

Protocols are needed to ensure that data are of acceptable quality, to record and store the data, and to analyse the data and present results.

How is air quality officially monitored in the EU?

Over recent decades, the EU has been working to continually improve air quality by controlling emissions of harmful substances into the atmosphere, improving fuel quality and integrating environmental protection requirements into the transport, industrial and energy sectors.

In Europe, the “Air Quality Framework Directive” on ambient air quality assessment and management (96/62/EC) was adopted by the European Council in September 1996. Supplementing the Air Quality Framework Directive was a series of ‘daughter’ directives. Subsequently, the Framework Directive and the First, Second and Third daughter directives have been brought together under the Ambient Air Quality and Cleaner Air for Europe (CAFE) Directive (2008/50/EC).

In the EU, the Air Quality Directives set threshold concentrations for the main air pollutants that shall not be exceeded in a given period and/or a certain number of times over a given period. These thresholds, called limit values, cover the following air pollutants: particulate matter (PM), nitrogen dioxide (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), benzene (C₆H₆) and lead (Pb). In the event of exceedance of a limit value, competent authorities are required to develop and implement air quality plans.

These plans should be designed to support efforts to bring concentrations of air pollutants below the limit values set for the protection of human health and the environment. When measuring air quality, member states must meet rigorous quality standards for accuracy and reliability. They are supported by AQUILA—the EU-wide network of air quality reference laboratories.

Spatial monitoring in Europe

Within the European Union, most countries have a substantial number of monitoring sites in operation. The networks in each state may be national, regional or local in area coverage, and different states have different organisations of monitoring responsibilities—national, regional or local authorities.

The largest states in the EU have the most sites. Examples: France (close to 900 sites), Germany (more than 500 sites), Spain (about 1000 sites), and the UK (more than 1200 sites).

On the other end of the scale, Albania has 23 urban sites, Greece has 32 sites (31 urban), Croatia has 41 sites (40 urban), Norway has 45 sites (6 urban), Denmark has 35 sites (18 urban), Hungary has 39 urban sites, and Estonia has 18 sites (16 urban/local).

Totally, the number of air quality monitoring sites in Europe is very large. For the 29 countries, there are close to 5 000 urban/local sites, and more than 800 regional sites.

Temporal monitoring in Europe

Most countries operate the networks the entire year. Exceptions are Norway and Sweden, where the monitoring is concentrated in the six winter months, which have the highest concentrations. For regional sites in Sweden, O₃ and NO₂ are monitored only in the six summer months. With a few exceptions, especially in East European countries, the monitoring/sampling covers all days/hours.

Let’s hear what Dr Martine Dennekamp has to say.