Experimental investigation of peat fire emissions and haze phenomena

Abstract

Emissions from peat fires, the largest fires on Earth in terms of fuel consumption, are the dominant source of haze episodes, especially in Southeast Asia. Haze is notorious for regional air quality deterioration, transport disruptions and respiratory and cardiovascular health emergencies. Despite their importance, current scientific understanding of peat fire emissions is limited, and the link to combustion dynamics has not been extensively considered in the literature. This knowledge gap impedes the development of mitigation strategies for peat fires. In this thesis, I investigated peat fire emissions through a series of laboratory and field-scale experiments. In the laboratory, a new experimental rig using advanced diagnostics was developed to quantify haze composition, fluxes and emission factors. The series of experiments revealed the roles of different peat soil properties (moisture content, inorganic content and bulk density) in fire dynamics and emissions. For the first time, transient gas and particulate matter (PM) emissions are shown to be significantly dependent on the combustion dynamics, and moisture content was found to have the primary influence on fire dynamics and the fire chemistry. Peat at high moisture content (160%, in dry basis) significantly reduces fire spread rate, decreases (> 50%) carbon and NH3 emissions, and limits PM emissions (< 25 g kg-1). An increase in inorganic content decreases fire spread rate, while an increase in bulk density delays emissions. The results also show that modified combustion efficiency (MCE), a fire behaviour proxy widely used in remote sensing and atmospheric sciences, fails to recognise smouldering combustion with sufficient accuracy, especially for wet peat with moisture content >120%. In addition to the lab experiments, a novel field experiment was carried out to quantify emissions from a tropical Indonesian peatland fire. I provide v the first field evidence indicating that changes in weather conditions (e.g., wind, rainfall) and the large inhomogeneity of soil properties in the field (e.g., bulk density and moisture content) affect the heat transfer and oxygen supply of peat fires, altering the fire dynamics, and thus introducing substantial variability into the emissions. This thesis provides a unique and comprehensive understanding of peat fire emissions, advancing our understanding of how haze is formed and how to mitigate against peat fire and haze.