UC Irvine

Fire impacts climate over wide spatial and temporal scales via many complex, interdependent, and often poorly understood processes. For example, fires emit substantial amounts of greenhouse gases and aerosols. Vulnerable regions worldwide are becoming more prone to larger, and more intense wildfires. Global change in the form of climate change and/or land use change is impacting fire regimes across the globe. In the boreal forest, climate change is causing a combination of warmer temperatures, drought, earlier snowmelt, and favorable fire weather that encourages the development of wildfires. In the tropics, specifically Indonesia, extensive land use change involving the degradation of naturally-existing peatlands to support agricultural productivity is also causing a significant increase in wildfires and corresponding emissions. There is a need to quantify and characterize the composition of emissions in wildfire-prone regions to fully understand the climate and human health related impacts of changing fire regimes.

In my first study, I examined the influence of daily meteorology on boreal forest fire emissions and regional trace gas variability. I coupled a statistical fire combustion model with an inverse atmospheric transport model to quantify the influence of fires on trace gas variability observed at a tower in Alaska equipped with a cavity-ring down spectrometer. I discovered that basic meteorological variables, including temperature and vapor pressure deficit, explained variability in fire activity better than complex fire weather indices. Next, I analyzed environmental controls on boreal forest fire emission factors during an anomalously large fire year in Alaska (2015). I used the same coupled modeling approach to determine times when fires influenced trace gas variability at the tower. Tower observations were used to calculate 23 individual boreal fire emission factors, substantially contributing to the database of emission factors. In my final study, I analyzed wildfire aerosol emissions in Indonesia during the devastating 2015 haze event. Considerable uncertainty exists with regards to whether the particulate emissions originate from deforestation fires, agricultural burning, or peatland fires. To address this, I analyzed aerosol samples collected in Singapore, a major city downwind of Indonesian wildfires, for their radiocarbon content. The radiocarbon content of the fire-emitted aerosol was depleted in 14C, indicating the majority of fire PM2.5 emissions originated from the burning of peatlands. The collective results of the studies from this dissertation will vastly improve our characterization of trace gas and particulate emissions from fires in globally important and vulnerable ecosystems.