Chemistry of Biomass Burning

Biomass combustion worldwide mainly comprises forest and grass fires, domestic fires and crop residue fires in agricultural fields. Depending on the type of biomass burned and the geographical location of the fire, emissions from combustion and their impact on air quality and climate will differ. However, the impact of forest fires is the biggest contributor to total biomass combustion emissions worldwide.

Forest and biomass fires are becoming increasingly common around the world. This can be partly linked to climate change, with adverse effects not only on local and regional air quality, but also on the global climate. The news of summer 2022 is a perfect illustration of this, with record fire episodes in France transporting pollutants several hundred kilometers. The second major event is the long period of wildfires in Australia in late 2019 and early 2020, impacting the composition of the troposphere and stratosphere at hemispheric level. We should also mention the recurrent forest fires in California and Canada every year, impacting local populations, regional air quality and hemispheric pollutant transport.

During biomass combustion phenomena (equatorial or mid- and high-latitude forests, savannahs...), a large quantity of chemical species is emitted (CH ₄ , CO, CO ₂ , NO _x = NO + NO ₂ ), but also oxygenated or non-oxygenated volatile organic compounds (VOCs) (aldehydes, acids...), accompanied by particles in the form of soot. The diversity and reactivity of the chemical species at the heart of the plume make it a large-scale chemical reactor where numerous species with varying lifetimes are formed, such as ozone and secondary organic aerosols.

Increasing fire frequency and intensity has led to high levels of VOCs and NOx for many years (from all sources) with an approximate doubling of ozone in the lower troposphere over the last two centuries, making ground-level ozone one of the most important anthropogenic greenhouse gases after carbon dioxide (CO ₂ ) and methane (CH ₄ ).

Observation and understanding of the phenomena occurring within biomass fires from source to transport are crucial to validate chemistry and climate models (regional and global) for long-term prediction of the impact of fires on air quality and climate.