Both prescribed burns and bushfires emit smoke plumes, which are visible because of the PM they contain. The smoke is the product of incomplete combustion. Fire emissions rates are affected by fire behaviour and the amount of fuel being burned. Fires can emit up to 1 per cent of the fuel load as PM to the atmosphere. Smoke particles have a life of hours to days and, because they often rise high into the atmosphere, they can travel long distances and affect people a long way from the fire. Smoke irritation includes itchy eyes, sore throat, runny nose, coughing and wheezing. The fine particles (and gases) are small enough to be breathed deep into the lungs and can cause health problems.
Australian weekly bushfire frequencies increased by 40 per cent in the 5 years to 2013, particularly during the summer months (Dutta et al. 2016). The increasing threat from bushfires has increased pressure for more prescribed burning — for example, the Royal Commission into Victoria’s 2009 bushfires recommended that there be a rolling annual target to burn 5 per cent of all public land. The emissions from these fires have increased pressure on air quality both close to the areas burned and in much larger urban areas affected by the smoke. Climate change is expected to increase these pressures.