Canberra has experienced its worst period of smoke-affected air quality since the 2003 bushfires, according to ACT Health, which monitors air quality year round to inform public health announcements.
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ACT Health public health physician Vanessa Johnston said bushfire events were difficult to predict and heavy smoke blowing into the city was not enough to issue a public health warning.
"We're continuously monitoring the air quality and in deciding whether we issue a public health alert, we have to consider a combination of things," she said.
"We consider the 24-hour rolling average against the national standard. We consider current real-time readings that we have available to us through the ACT government laboratory. We consider the time of the day. ... And then we look at the forecast weather conditions to estimate the intensity and duration of that exposure."
Advice is based on 24-hour rolling average readings of particulates in the air because that better reflects the impact from continued exposure. Instantaneous measurement of air quality often fluctuates and gives a poor indication of the longer term exposure which poses a public health risk.
Air quality in the ACT also drops on winter nights when wood-burning heaters push out smoke, but public health warnings are often not issued in those periods because most people would be indoors and unlikely to be exposed, Dr Johnston said.
She said the advice for people sensitive to smoke was to avoid exposure and for all people to avoid strenuous outdoor activity.
Masks did provide help if they had a filter rated to capture airborne particulates but needed to have a snug fit.
"These masks are generally not available for children and wouldn't necessarily be suitable for people with beards, for example. It has to be a very tight, clean fit for them to be effective. But it is definitely an option," Dr Johnston told the Sunday Canberra Times.
After bushfires in Canberra in January 2003, the air quality index - which takes into account other air pollutants alongside smoke - peaked at 650, 6.5 times the national standard. This was the highest reading in the ACT. In the past week the index peaked at 596.
The director of environmental chemistry at ACT Health, Ian Fox, said the ACT had not recorded anything as high as the past week's peak in the time since 2003.
Mr Fox said the three air quality monitoring stations - in Monash, Florey and the city centre - were inspected twice a week and air filters retrieved to be weighed and the collected particulate matter analysed.
ACT Health has seen more than a 1000 per cent increase in web traffic to air quality update information since smoke from bushfires burning in the Tallaganda National Park near Braidwood and at Currowan north-west of Batemans Bay began affecting air quality.