Fine particle emissions from tropical peat fires decrease rapidly with time since ignition

Abstract

Southeast Asia experiences frequent fires in fuel‐rich tropical peatlands, leading to extreme episodes of regional haze with high concentrations of fine particulate matter (PM2.5) impacting human health. In a study published recently, the first field measurements of PM2.5 emission factors for tropical peat fires showed larger emissions than from other fuel types. Here we report even higher PM2.5 emissions factors, measured at newly ignited peat fires in Malaysia, suggesting current estimates of fine particulate emissions from peat fires, may be underestimated by a factor of three or more. In addition, we use both field and laboratory measurements of burning peat to provide the first mechanistic explanation for the high variability in PM2.5 emission factors, demonstrating that build‐up of a surface ash layer causes the emissions of PM2.5 to decrease as the peat fire progresses. This finding implies that peat fires are more hazardous (in terms of aerosol emissions) when first ignited than when still burning many days later. Varying emission factors for PM2.5 also has implications for our ability to correctly model the climate and air quality impacts downwind of the peat fires. For modelers able to implement a time varying emission factor, we recommend an emission factor for PM2.5 from newly ignited tropical peat fires of 58 grams of PM2.5 per kilogram of dry fuel consumed (g.kg‐1), reducing exponentially at a rate of 9% per day. If the age of the fire is unknown or only a single value may be used, we recommend an average value of 28 g.kg‐1. Plain Language Summary This paper provides evidence that peat fire emissions of fine particulates are much larger than for other fires when the peat is newly ignited but decrease rapid as the fire progresses. This is important because it means that newly ignited fires are particularly detrimental to ambient air quality in impacted regions