Transient gas and particle emissions from smouldering combustion of peat

Smouldering combustion of peat drives the largest fires on Earth, and their emissions play an important role in global carbon balance and regional air quality. Here we report a series of controlled laboratory experiments of peat fires. Peat samples of 100% moisture content in dry basis were burnt in an open-top reactor with dimensions of 20 × 20 × 10 cm. The diagnostics are a unique set of simultaneous measurements consisting of real-time mass loss, up to 20 different gas species concentration, size-fractioned particle mass (PM10, PM2.5 and PM1), temperature profile, and visual and infrared imaging. This comprehensive framework of measurements reveals that the evolution of the emissions varies in time with four observed stages (ignition, growth, steady and burn out) which are characterised by different combustion dynamics. Mass flux measurements show that CO2, CO, CH4 and NH3 are the four most predominant gas species emitted in the steady stage. Incorporating the mass loss rate, the transient emission factors (EFm) of both gas and particle species are calculated and reported here for the first time. Averaging the steady stage, the EFm of PM2.5 reached 23.12 g kg-1, which accounts for 87.2% of the total particle mass, and PM1 EFm was reported to be 15.04 g kg-1. The EFm of alkane species (CH4, C2H6, C3H8, C4H10) were found to peak within the ignition stage, whereas the EFm of CO2, CO and NH3 kept increasing during the steady stage. Because of these measurements, for the first time we were able to validate the EF calculated by assuming averaged values and a carbon balance, which is the preferred method used in remote sensing and atmospheric sciences. This work contributes to a better understanding of peat fire emissions and could help develop strategies tackling regional haze.