Review of emissions from smouldering peat fires and their contribution to regional haze episodes

Smouldering peat fires, the largest fires on Earth in terms of fuel consumption, are reported in six continents and are responsible for regional haze episodes. Haze is the large scale accumulation of smoke at low altitudes in the atmosphere. It deteriorates air quality, disrupts transportation and causes health emergencies. Research on peat emissions and haze is modest at best and many key aspects remain poorly understood. Here, we compile an up-to-date inter-study of peat fire emission factors (EFs) in the literature both from laboratory and field studies. Tropical peat fires present larger EFs for the prominent carbon gas species than boreal and temperate peat fires, possibly due to the higher fuel carbon content (56.0% vs. 44.2%). In contrast, tropical peat fires present slightly lower PM2.5 EFs for unknown reasons but probably related to combustion dynamics. An analysis of the modified combustion efficiency, a parameter widely used for determining the combustion regime of wildfires, shows it is partially misunderstood and highly sensitive to unknown field variables. This is the first review on smouldering peat emissions and haze. Our integration of the existing literature, allows for the identification of existing gaps in knowledge and is expected to accelerate progress towards mitigation strategies.