Title: Fire and Aerosol Modeling for Air Quality and Climate Studies
Description: Open burning of biomass and anthropogenic waste is a major source of aerosols at the biosphere-atmosphere interface, yet its impact on Earth’s climate and air quality is not fully understood due to the intricate feedbacks between the natural environment and human activities. Earth system models (ESMs) are a vital tool in the study of these aerosol-biosphere-atmosphere interactions. ESMs allow the estimation of radiative forcing and climate impacts in terms of changes to temperature and precipitation as well as the attribution to natural or anthropogenic drivers. To provide coherent results, however, ESMs require rigorous development and evaluation against observations. In my work I use the NASA-GISS ESM: ModelE. One of its strengths lie in its detailed aerosol schemes that include microphysics and thermodynamic partitioning, both necessary for the simulation of secondary inorganic aerosols. To overcome one of ModelE’s weaknesses, namely its lack of interactive biomass burning (BB) emissions, I developed pyre: ModelE’s interactive fire emissions module. pyrE is driven by flammability and cloud-to-ground lightning, both of which are calculated in ModelE, and anthropogenic ignition and regional suppression parameterizations, based on population density data.

Notably, the interactive fire emissions are generated from the flaming phase in pyrE (fire count), rather than the scar left behind (burned area), which is commonly used in other interactive fire modules. The performance of pyrE was evaluated against MODIS satellite retrievals and GFED4s inventory, as well as simulations with prescribed emissions. Although the simulated fire count is bias-high compared to MODIS, simulated fire emissions are bias-low compared to GFED4s. However, the bias in total emissions does not propagate to atmospheric composition, as pyrE simulates aerosol optical depth just as well as a simulation with GFED4s prescribed emissions. Upon the development and evaluation of the fire-aerosol capabilities of ModelE, I have utilized it, with the EVA health model, to study the health impacts of outdoor smoke in 1950, 2015, and 2050. I find that chronic exposure to aerosols (PM2.5) is the main driver of premature deaths from smoke exposure, yet by 2050, acute exposure to ozone, formed downwind of BB smoke plumes, is projected to cause more premature deaths than exposure to PM2.5.

I estimate the annual premature deaths from BB and waste burning (WB) smoke in 1950 to be ~41,000 and ~19,000, respectively, and in 2015 to be ~310,000 and ~840,000, respectively. By 2050 I project 390,000 and 1.5 million premature deaths from BB and WB respectively. In light of the growing impact of WB smoke exposure I identify the need to scale up viable waste management practices in regions of rapid population growth.