Abstract
Prescribed burns produce smoke pollution, but little is known about the spatial and temporal pattern because smoke plumes are usually small and poorly captured by State air-quality networks. Here, we sampled smoke around 18 forested prescribed burns in the Sydney region of eastern Australia using up to 11 Nova SDS011 particulate sensors and developed a Generalised Linear Mixed Model to predict hourly PM2.5 concentrations as a function of distance, fire size and weather conditions. During the day of the burn, PM2.5 tended to show hourly exceedances (indicating poor air quality) up to ~2 km from the fire but only in the downwind direction. In the evening, this zone expanded to up to 5 km and included upwind areas. PM2.5 concentrations were higher in still, cool weather and with an unstable atmosphere. PM2.5 concentrations were also higher in larger fires. The statistical model confirmed these results, identifying the effects of distance, period of the day, wind angle, fire size, temperature and C-Haines (atmospheric instability). The model correctly identified 78% of hourly exceedance and 72% of non-exceedance values in retained test data. Applying the statistical model predicts that prescribed burns of 1000 ha can be expected to cause air quality exceedances over an area of ~3500 ha. Cool weather that reduces the risk of fire escape, has the highest potential for polluting nearby communities, and fires that burn into the night are particularly bad.
Highlights
Prescribed burning is a common strategy for reducing many aspects of wildfire risk, effects that have been quantified in many studies around the world
Di Virgilio, Hart [14] identified days when prescribed burns occurred in the Sydney region and investigated the weather conditions that influenced whether those days had elevated PM2.5 levels
The temperature effects showed a similar split according to the time of day, with higher temperatures associated with higher PM2.5 concentrations in the day time, but lower temperatures associated with high concentrations in the evening and night
Summary
Prescribed burning is a common strategy for reducing many aspects of wildfire risk, effects that have been quantified in many studies around the world. Navarro, Schweizer [12] reviewed observational studies in the USA and found only seven empirical studies of prescribed burning These reported higher levels of particulates than studies of wildfire, but they were not directly comparable because the measurements were closer to the exposed communities. Di Virgilio, Hart [14] identified days when prescribed burns occurred in the Sydney region and investigated the weather conditions that influenced whether those days had elevated PM2.5 levels. They found that cool, stable conditions with light westerly winds were associated with smoke impacts in Sydney. The objective was to identify weather conditions that are likely to cause greater smoke impact (so they can be avoided) and predict the distance that pollution will spread to improve the ability of fire authorities to manage risks to communities
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