Climate Impacts of Biomass Burning Aerosols: Constraining the Chemicophysical Properties of Fresh and Aged Particles
Biomass burning is one of the largest contributors of particles and trace gases to the atmosphere. This work focuses on constraining the impacts that biomass burning has on Earth's climate through two effects: scattering or absorption of light by particles and particle impacts on cloud formation. To explore biomass burning light interaction and hygroscopicity, a series of environmental chamber experiments were carried out using fuels common to the southwest U.S. This work includes the effects that photochemical aging has on the emissions to provide a realistic assessment of the emissions' lifetime in the atmosphere.
The work done on the cloud formation properties of the emissions shows that two common assumptions applied to the emissions misrepresent their cloud forming abilities. The first assumption, that surface active compounds are negligible in cloud activation, is shown to not apply to biomass burning aerosols. Not accounting for the presence of surface active compounds over estimates the hygroscopicity of the aerosols by up to 30%. The second assumption, that the volume of the particles is well characterized by the electrical mobility diameter, is also shown to not apply to the system. Making the second assumption when parameterizing the hygroscopicity of the aerosols underestimates the hygroscopicity by up to 50%. Accounting for both assumptions is shown to have a greater impact at the point of emission than after six hours of photochemical aging. Therefore, the age of the aerosols must be taken into account when predicting the indirect effects of biomass burning aerosol.
This work also explores the light absorption of biomass burning aerosol and its reaction to photochemical aging. The results indicate that the aerosol is light absorbing and the magnitude of absorption can change with photochemical exposure. This work also shows that the absorption of the aerosol evolves with the volatility and surface active compounds present in the aerosol.
The final part of this work demonstrates that the local air quality that biomass is grown in can have an impact when that biomass is burned. Biomass grown in a polluted area is shown to emit more NOx than biomass grown in a clean area and that the aerosols are less volatile.