Indicator: Outdoor Air Quality
Summary of results
This reporting period was unusual because of the intense and prolonged bushfires in and around the ACT. These, as well as dust-storms, caused higher levels of airborne particulate matter than in the past. The National Environmental Protection Measure (NEPM) goal for particulate matter of no more than five exceedences per year was not met. There were 17 exceedences at Monash in the year ended 30 June 2003, and 22 exceedences during the whole reporting period.
The bushfires also caused higher levels of other monitored pollutants, and an exceedence of both the one-hour and the four-hour ozone value was also recorded in January 2003. The NEPM’s goal is only one exceedence per year.
Apart from the pollution caused by the fires, the ACT continues to meet most NEPM standards most of the time, and air quality is generally good in Canberra, given that it is an urban area. Solid fuel-burning for domestic heating and operation of motor vehicles continue to be the main factors reducing the city’s outdoor air quality.
There are no strong trends in the concentration of monitored pollutants, apart from the steady decline of airborne lead, which has now reached such low concentrations that continued monitoring is not worthwhile.
What the results tell us about the ACT
Concentrations of airborne particles (particulate matter with particles smaller than 10 micrograms, or PM10) usually remain below the National Environmental Protection Measure (NEPM) value of 50 micrograms of matter per cubic metre of air, although occasional exceedences occur in most years. The NEPM goal is for no more than five exceedences per year.
During the reporting period the Monash recording site registered 22 exceedences of the NEPM for PM10, but there were some data absences. Before 14 March 2002, PM10 levels were recorded only once every six days at Monash, a rate that is unlikely to pick up all exceedences. There are also no data for the period of the Christmas 2001 fires. Nonetheless, it is certain the goal of no more than five exceedences per year was not met.
During the reporting period, Civic recorded three exceedences, but it should be noted that PM10 continues to be measured only every sixth day at Civic. Furthermore, the Civic monitoring station was moved from the Petrie Street car park to a new location between Civic swimming pool and the YMCA, and the two monitoring sites were not run in parallel. This means differences between the sites could not be assessed, and new data cannot be reliably compared to old. Also, the new Civic monitoring station was not functioning during January and February 2003. Multiple monitoring stations, taking daily readings, are recommended as a way of checking any anomalies and for insurance should one site become temporarily inoperable.
Impacts of bushfires and dust storms on levels of airborne particles
The January 2003 bushfires injected a massive quantity of particles into the air, and this shows up quite clearly in measured values at both Civic and Monash. On 18 January 2003, the day of the main Canberra fires, Monash recorded a reading of 193 micrograms of matter per cubic metre. Values remained high on many other days in January, reaching nearly 328 micrograms of matter per cubic metre on 30 January.
Even this value was exceeded during the duststorm of 20 March, when Monash recorded 350 micrograms of matter per cubic metre, which is seven times the NEPM. Eroded soil particles were carried from further inland and coated Canberra cars and buildings in a fine red patina. The days before and after that reading both yielded ‘normal’ values, close to 20 micrograms of matter per cubic metre.
A NEPM for PM2.5 (much finer particles, smaller than 2.5 micrograms) was agreed to in June 2003 with monitoring to start in June 2004. The ACT Government has financed purchase of relevant equipment, which is being prepared and tested to start PM2.5 analysis at Monash in January 2004. Results and analysis should be presented in the next report.
A main source of airborne particles in the ACT related to human activity is wood-burning heaters. Smoke particles, and other pollutants produced by wood burning, are a particular problem when atmospheric inversion layers, especially in valleys, do not allow them to disperse. The ACT Government has announced that, from 1 January 2004, it will offer a subsidy to households to replace older, high-emission wood heaters.
New nephelometer network
An ACT-wide array of nephelometers, which measure haze, will help provide better information on the true extent of smoke pollution. An additional $50,000 will be spent in 2004–05 to buy extra nephelometers. Once a correlation has been determined between these instruments and the PM2.5 instrument they will be able to be used for campaign or mobile monitoring.
It is hoped the new measures to be introduced will allow greater coverage of air quality monitoring across the ACT, especially in the north of Canberra. The lack of any north Canberra air quality data since the closure of the Belconnen monitoring site in June 1996 continues to be of concern.
There is no discernible long-term trend in carbon monoxide levels, but the data show the usual pattern of winter peaks and summer troughs. Winter values are three to four parts per million in Monash (Figure 3) and five to six parts per million in Civic (Figure 4). Summer values usually remain less than 1 part per million in Monash and hover between zero and 1.5 parts per million in Civic. The higher concentrations in winter are thought to be due mainly to solid fuel burning (wood smoke). The recorded concentrations at all monitoring sites remain below the NEPM value of 9 parts per million over an eight-hour period. There were some unseasonally high 8-hour readings in Monash in January 2003, probably related to the bushfires. The values were still below the NEPM and below those commonly found on winter days.
Concentrations of airborne lead are now only slightly above the normal background level of nonurban air. In the 1980s, lead concentrations were much higher, frequently exceeding the guidelines of the time. The dramatic decline in this pollutant is clear from Figure 5, which shows lead recorded at all monitoring stations from 1990. Because of these continuing low concentrations, airborne lead is no longer routinely monitored. The data demonstrate a clear success story of environmental improvement through legislated action. There is no longer any significant source of lead emissions to the air in the ACT, since the change-over to lead replacement fuel means that even older motor vehicles do not use leaded fuel.
There is no discernible trend of atmospheric nitrogen oxide levels over the years. One-hour concentrations at the two monitoring locations (Monash and Civic) hovered around the 0.02 parts per million level, with occasional peaks to 0.04 parts per million or even, on one occasion in Civic, 0.9 parts per million (Figures 6 and 7). This is well below the National Environment Protection Measure onehour standard of 0.12 parts per million.
In this reporting period, both NEPM standards for ozone were exceeded on one occasion in Monash; and Civic also came close to exceeding the standards. This is unusual, but the high levels occurred in January 2003, when the bushfires would undoubtedly have contributed.
The highest reported value for 4-hourly ozone occurred on 21 January 2003, when Monash recorded 0.02 parts per million (the NEPM standard is 0.08). The one-hour standard of 0.1 parts per million was exceeded in Monash on 18 January 2003, with a value of 0.102 parts per million (see Figure 10).
Apart from during the bushfire period, four-hour concentrations were generally in the region of 0.02–0.04 parts per million (Figures 8 and 9). This is well below the NEPM four-hour standard (of 0.08 parts per million). The same is true for onehour concentrations, which fluctuated between about 0.02–0.04 parts per million at both monitoring sites (see Figure 10 for Monash data).
There is no discernible long-term trend in the concentration of ozone, although there is a slight seasonal pattern, with slightly higher concentrations in the summer. This is mainly due to the influence of sunlight in forming ozone in the lower atmosphere. Most of this ozone is not directly emitted; it is a secondary pollutant, formed by the action of sunlight on emitted pollutants, such as nitrogen oxides and volatile organic compounds, most of which come from vehicle exhaust, although the bushfires of January 2003 were also a major source.
All monitoring of airborne pollutants is carried out by the ACT Government Analytical Laboratory (ACTGAL) on behalf of Environment ACT.
The standards set under the Air Quality NEPM are listed in Table 1.
|Pollutant||Averaging period||Maximum concentration||Maximum allowable exceedences*|
|Airborne particles (as PM10)||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|
* to be fully achieved by 2008
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 PM10, which may be exceeded no more than five days per year).
The National Environment Protection Council website http://www.ephc.gov.au gives more information about NEPMs.