This case study looks at the severe fires experienced across parts of Indonesia in August to October 2019, and the resulting severe air pollution that was generated.

Smoke from peatland and forest fires in Central Kalimantan, located on the island of Borneo, was sampled using ground-based measurement devices. The fires themselves were imaged from unmanned aerial vehicles. These kind of insitu measurements enable precise investigations of both the fires and the composition of the smoke, complementing data obtained from satellites.

These peatland fires often start at the surface in the vegetation layer, but then move underground into the carbon-rich peat where they can smoulder for days, weeks or even longer. Smouldering combustion is particularly effective at producing smoke rich in air pollutants – such as carbon monoxide and fine particulate matter. In the cities surrounding the fires, this smoke led to some of the worst air quality conditions ever measured in urban areas, even cities of hundreds of thousands of people. In Palangkaraya in Central Kalimantan PM_2.5 concentrations rose to well over 1000µg.m^-3  - which is far higher than the World Health Organisation considers ‘extremely hazardous to health’ and many tens of times that found in Central London on a bad air quality day.  The smoke travelled great distances to also affect neighbouring countries, and this smoke transport was seen very clearly from space.

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On the ground, an infrared spectrometer was utilised to measure the composition of the smoke. The instrument works by measuring the absorption of infrared light by the smoke. An infrared lamp was positioned some tens of meters away from the receiver, and light from the lamp was measured at different wavelengths using the receiving spectrometer. Particular wavelengths of light are absorbed by different gases in the smoke, acting like a fingerprint to identify the individual gaseous species present. The depth of the absorption features produced by each gas can also be used to determine its concentration. As a result, these measurements can be used to determine both what gases are emitted by the fire, and in what ratios. From these ratios, so-called gaseous ‘emission factors’ can be derived, and these represent the amount of a particular species that is emitted per kg of dry vegetation or organic soil burned. These emissions factors are used in models that convert satellite data of fires into estimates of fire emissions, and which underpin many atmospheric models that use fire emissions data as inputs.

Featured Educator

• Professor Martin Wooster, Professor of Earth Observation Science, KCL

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