ACT State of the Environment 2007

Indicator: Outdoor air quality


Outdoor air quality in the Canberra urban area generally remained good throughout the reporting period.

National Environment Protection (Ambient Air Quality) Measure (NEPM) standards were met for all measured pollutants with the occasional exception of particulate matter (PM) (see Air emissions indicator). As well, one-hourly values for ozone were breached on 31 December 2006 and 1 January 2007.

No dramatic long-term trends were apparent in the monitored pollutants, although there was an interesting hint of improvement in carbon monoxide. Airborne lead is no longer monitored, as its level is now so low; and there is no need to monitor sulphur dioxide in the Territory, as there are no significant sulphur dioxide emission sources in the area.

What the results tell us about the ACT

The results clearly show that Canberra enjoys good air quality most of the time. However, unlike other jurisdictions, Canberrans know little about the air quality in our city.  It is important the Canberrans have a better understanding of the quality of air they are breathing and the effects our actions and choices have on our air quality.  The city is fortunate that it has no heavy industry, mining, ore processing or other activities that are known to adversely affect air quality. Despite heavy and growing motor vehicle use, the city is sufficiently dispersed to mitigate any potentially health-damaging build up of emitted pollutants.

The main cause for concern arises from airborne particles occasionally exceeding desirable values. This can happen naturally or as a result of human activity. Bushfires and dust storms are the principal natural causes, and they occur mainly during summer; and wood-burning heaters are an important anthropogenic cause during the cooler months.

The monitoring station in the southern suburb of Monash recorded isolated breaches of the PM 2.5 NEPM in the winter of each year during the reporting period. The Civic centre does not monitor PM 2.5, but it does monitor PM 10; one or two exceedences of PM 10 were recorded in both Civic and Monash, but these mainly occurred during summer (especially in November/December 2006 and January 2007). These spikes were probably caused by drift from extensive bushfires near Tumut (New South Wales) and Gippsland and northeast Victoria.

Data captured before March 2007 is considered suspect as work to stabilise the air conditioning in the balance room was not completed until March 2007. Part of the quality control for the PM 2.5 is that the balance room where the filters are weighed is kept within a specified range for temperature and relative humidity. It is thought that changes in the temperature and relative humidity may have affected the weights of the filter and/or its contents. Quality control testing of blank filters does not show a significant change in the filter weights between weighing sessions.

Breaches of the NEPM standard for ozone occurred in Civic in 2006, but there were no breaches in 2004 or 2005. For four-hourly ozone monitoring, the NEPM was breached once, with a maximum recorded value of 0.145 parts per million (ppm) on 20 December 2006 (the NEPM standard is 0.08 ppm). This was the only exceedence in that year; the NEPM goal permits one exceedence day per year for ozone. However, the hourly value for ozone was exceeded more than once in December 2006, with the highest value being 0.25 ppm (the NEPM is 0.1 ppm).

Monash did not record any exceedences for ozone. Theory predicts that ozone values would be lower in Monash than in Civic, and the data support this. The reason is that ozone is formed when sunlight promotes chemical reactions among pollutants that are emitted from motor vehicles. Civic's higher concentration of motor vehicles is the culprit, and if the city centre becomes more congested with vehicular traffic more exceedences of ozone will occur in the summer, and greater concentrations of carbon monoxide and nitrogen dioxide will occur year round.

Airborne lead

Monitoring ceased in 2002 because values were so low.

Carbon monoxide

Graphs of carbon monoxide measurements (102 kB pdf)

Neither monitoring site recorded any breaches of the NEPM for carbon monoxide. There is a seasonal pattern, with higher values in the winter. A slight diminution in the values is discernible in the data from 2000 to 2007. This could be an encouraging trend, although it is too early to say if it represents a genuine reduction or a random fluctuation. Reasons for a decline in carbon monoxide values could be a decline in the popularity of wood burning heating (which is the main cause of the emissions – hence the seasonal peaks in winter). Anecdotally, it is believed that newer houses are less likely to use wood burning heating although there is no hard data to this effect.

Nitrogen dioxide

Graphs of nitrogen dioxide measurements (109 kB pdf)

All values at both monitoring sites are well below the NEPM standard. There is no clear long-term trend.


Graphs of ozone measurements (133 kB pdf)

Exceedences occurred in both four-hourly and one-hourly ozone values in Civic. There were no exceedences in Monash in the reporting period. There is no discernible long-term trend in the series from 2000 to 2007.

Particulate Matter

Graphs of airborne particulate measurements (90 kB pdf)

Particulate matter (PM), also known as airborne particles, refers to material that is emitted into the air and, because it is so small, floats there for a prolonged period. The material is categorised according to size; PM 10 means all particles with a diameter of less than or equal to 10 micrometres and PM 2.5 refers to a category of smaller particles, namely all those whose size does not exceed 2.5 micrometres in diameter.

Until June 2003, legislation only required that PM 10 be monitored. However, in 2003 the National Environment Protection Council decided that PM 2.5 should be monitored separately. This decision was based on accumulated evidence that the smallest particles are the most dangerous to health as they remain airborne for longer, and can reach further into the lungs without being readily filtered out. A total figure for the concentration of PM 10 in the air does not reveal whether most of the particles are in the upper end of the size range or, more dangerously, the lower end. Therefore the new standard was proposed. New equipment was required, and the ACT started monitoring PM 2.5 in June 2004.

Monash monitors both PM 2.5 and PM 10; Civic monitors only PM 10. The NEPM permits exceedences on five days per year. PM 2.5 values were exceeded in Monash 47 times during the reporting period.

The ACT Government Analytical Laboratory carries out all monitoring of airborne pollutants on behalf of Environment ACT (Environment Protection, TAMS). The NEPM air quality standards are listed in Table 1. For averaging times shorter than one year, compliance with the NEPM goal is achieved if the standard for a pollutant is exceeded on no more than a specified number of days in a calendar year (one day per year for all pollutants except PM 10, which may be exceeded no more than five days per year). The National Environment Protection Council website at gives more information about NEPMs.

Table 1: Standards and goal
Pollutant Averaging period Maximum concentration Maximum allowable exceedences*
Airborne particles (as PM 10) 1 day 50 µg/m3 5 days a year
Carbon monoxide 8 hours 9.0 ppm 1 day a year
Lead 1 year 0.50 µg/m3 none
Nitrogen dioxide 1 hour 0.12 ppm 1 day a year
1 year 0.03 ppm none
Ozone (photochemical oxidants) 1 hour 0.10 ppm 1 day a year
4 hours 0.08 ppm 1 day a year
Sulfur dioxide 1 hour 0.20 ppm 1 day a year
1 day 0.08 ppm 1 day a year
1 year 0.02 ppm none

Note: * to be fully achieved by 2008; Source: National Environment Protection Council

Data sources and references

ACT Government Analytical Laboratory

National Environment Protection Council website at last viewed 28 March 2008

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