The fundamental objective of air quality monitoring is to collect data that can be used to make informed decisions to best manage and improve the environment. This section describes an approach for developing an air quality monitoring strategy.
2.1 Regional policies and plans
Monitoring programmes should be closely linked to the main issues of concern within a region, as specified in its regional plan. Air quality monitoring provides evidence on the current levels of contaminants and provides policy-makers with information on how to better manage air quality in their regions.
Air quality data is continuously collected to provide information to aid policy development and evaluation. After a regional plan has been put in place, monitoring can confirm if targets are being met and if the rules implemented are producing the anticipated results.
Compulsory monitoring requirements were also introduced when the NES for air quality were implemented in 2004. Regional councils should consider these requirements when drafting their regional plans and monitoring programmes.
2.2 Regional monitoring objectives
To quantify ambient air quality in a region and note spatial and temporal variations, the monitoring should:
provide comprehensive data to judge the significance of actual and perceived regional issues
be related to the issues, objectives and methods of implementation specified in the regional air plan
supply sufficient data to determine geographical patterns in air quality over various time scales (eg, seasonally)
lead to an understanding of whether national or regional air quality standards, guidelines, objectives and environmental outcomes are being met, and whether areas of concern are being identified
develop a picture of representative concentrations in areas of high population density where air quality is known, or suspected, to be poor
provide sufficient data to determine trends in air quality over time and the background levels of contaminants
supply enough information to determine the population at risk from exposure to poor air quality in order to evaluate the potential and actual health effects in a region (eg, personal exposure assessments).
2.3 Developing an air quality monitoring programme
The intended use of data from a monitoring site should be identified before a site is established.
Usually, the general objective of an ambient air quality monitoring programme is to determine air quality in a region to assess its effects on human health. However, programmes may have different specific objectives (eg, to establish long-term trends and patterns, or validate dispersion modelling).
There are many factors to consider in developing a monitoring programme, but the following are of fundamental importance.
Why is monitoring being undertaken? What is the expected outcome of the monitoring? Establishing a monitoring objective is the fundamental step in developing a monitoring programme because all subsequent decisions will be based on why the monitoring is being undertaken. The most common reasons for monitoring include:
- determining the level of contaminants in an airshed to compare with standards and guidelines
- reporting on the state of the environment
- obtaining exploratory data
- conducting air quality research
- obtaining data for air quality modelling
- providing air quality information for policy or strategy development
- assessing the effectiveness of policy based on air quality trends.
Which species to monitor?
In many cases this may be obvious, based on known emission sources in the area, but in other cases it merits careful consideration. Once the target contaminant has been identified, in what form should it be monitored? For example, total hydrocarbons or individual (speciated) hydrocarbons? Total particulate matter or a specific size fraction? Is further analysis required?
How to sample?
Both the type of sampling and the analytical end method need to be considered. Method selection involves an appraisal of cost versus performance; the latter includes the limits of detection, sensitivity, speed of instrument response, susceptibility to interfering species and the overall uncertainty of the measurement. Consider the aim of monitoring and choose appropriate methods and equipment. When using a screening method for exploratory testing, is the level of accuracy and precision suitable to measure contaminant levels?
Where to sample?
The decisions around where to locate a monitoring site are based on the objectives of monitoring. The siting of an air quality monitor has a profound effect on the resulting measurements of contaminant levels and on achieving monitoring objectives. Will the site measure peak or background concentrations? What atmospheric reactions affect the formation/destruction of the contaminant to be monitored?
How to calibrate and maintain equipment?
Calibration and maintenance of monitoring equipment is an important part of every monitoring programme. How frequently should calibration be undertaken? What documentation is required? What procedures will ensure the efficient and smooth operation of monitoring equipment?
What data management protocols should be used?
It is important to ensure that air quality data is properly validated and managed after it is obtained. What data quality assurance processes are in place? What supplementary data needs to be collected? Other information may be relevant to the study (eg, meteorological conditions, process data and traffic flows). Meteorological conditions are important in assessing the impacts of sources on surrounding areas because they dictate the transport and dispersion of contaminants in ambient air.
How will data be stored and reported?
What time format should be used? How will exceedences be determined and reported? Following the recommended format in the reporting of monitoring results is a step towards achieving national consistency in air quality reporting.
These factors are discussed in greater detail in the following chapters.
2.4 Desktop assessments
In the early stages of establishing a regional monitoring programme little may be known about the air quality of the area under investigation. Initially, it will be necessary to assess where air quality in the region is likely to be at risk of exceeding standards for each contaminant. This can often be done by a desktop assessment.
The following factors need to be investigated to determine areas at risk within a region:
emissions sources (eg, domestic, industrial, transport, agricultural and natural) and the contaminants emitted
meteorology (eg, areas prone to temperature inversions)
population centres (especially where domestic fires and traffic emissions occur)
historical monitoring data (where available)
areas with high natural environmental values (eg, in and around natural parks, forests, wilderness areas and wetlands)
the location of sensitive areas particularly vulnerable to air pollution (eg, hospitals, schools, child- and aged-care facilities)
areas planned for development (eg, to get a picture of background concentrations)
any public complaints or issues of concern relating to air pollution
any epidemiological studies on air quality effects on health already carried out.
This information should provide a good basis to determine which contaminants should be monitored and where contaminant levels may be elevated. Should any risks be identified, preliminary screening surveys may need to be established to better identify risk areas and potential contaminant levels, particularly if no historical monitoring data is available. Even with a well-established regional monitoring programme, emission sources within an air quality management area can change significantly over time (requiring an efficient approach to updating emission inventories), and may result in the need for further screening surveys.
2.5 Types of monitoring
2.5.1 Screening surveys
Screening surveys using local knowledge and simple monitoring techniques can provide a quick and cost-effective picture of contaminant concentrations over a wide spatial distribution. They are usually intended to assess air quality at a particular location to determine indicative ambient concentrations and identify whether more permanent monitoring is needed. Screening surveys can include non-standard methods such as passive samplers for gases and volatile organic compounds (VOCs) and low-volume gravimetric samplers for PM10. However, the use of standard methods housed in a mobile air quality monitoring station may be more appropriate where decisions on establishing permanent sites (at considerable financial investment)
Consideration should be given to ensuring the monitoring period is representative of pollution levels throughout the year. Screening should ideally be undertaken for at least a six-month period to include summer and winter conditions. Screening surveys should cover particular seasons in which contaminant peak levels occur.
2.5.2 Continuous monitoring
Screening programmes should only be used to provide an indication of where detailed monitoring is required. Data derived from screening surveys must not be used to determine whether an airshed complies with the NES for air quality or air quality guidelines. When there is an indication that national standards are likely to be breached, it will be necessary to select sites where contaminants will be monitored using the methods in Schedule 2 of the NES for air quality. This is likely to require commitment to a long-term site in order to measure the effects of management strategies in the airshed.
Two examples of continuous monitoring sites are:
permanent ambientsite – a site established for long-term monitoring of contaminant levels and trends using standard monitoring methods
compliance monitoringsite – a site established for long-term monitoring of contaminant levels and trends over time for the purposes of determining compliance with the NES for air quality in a particular airshed. The use of standard monitoring methods is compulsory.
2.5.3 Monitoring for research purposes
Air quality monitoring is often undertaken for research purposes to address specific issues such as local dispersion characteristics using tracer gases, or the collection of particle samples for speciation analyses and source apportionment work. This work is usually carried out using non-standard methods and specialised sampling equipment.