Skip to main content
eScholarship
Open Access Publications from the University of California

UC Berkeley

UC Berkeley Electronic Theses and Dissertations bannerUC Berkeley

Variability in wildfire emissions of nitrogen oxides as observed from space

  • Author(s): Mebust, Anna
  • Advisor(s): Cohen, Ronald C
  • et al.
Abstract

Wildfires are a significant source of nitrogen oxides (NOx = NO + NO2) to the global atmosphere, representing approximately 15% of the total NOx budget. Fire conditions that govern NOx emission vary significantly from fire to fire, resulting in highly variable emissions. Emissions from fires burned in a laboratory setting fail to reproduce the conditions in which large wildfires occur, such as fire size and meteorology; however, in situ measurements of fire emissions are challenging to make, in part due to the destructive nature of large wildfires. As a result, systematic variability of NOx emissions--even when normalized for biomass burned--across or within biomes is poorly understood and documented.

In this dissertation, I demonstrate that the high spatial and temporal coverage of space-based observations can be used to greatly increase the number and scope of available observations of actively burning wildfires. I derive a method to estimate NOx emission coefficients (ECs in g NOx MJ-1) using NO2 column densities from the Ozone Monitoring Instrument (OMI) and fire radiative power from the Moderate Resolution Imaging Spectroradiometer (MODIS), two Earth-observing satellite instruments. I show that this method, when applied in California and Nevada, reproduces differences in fire emission factors (EFs in g NOx kg-1) between fuel types that have been previously observed using in situ measurements. I then identify and explore sources of variability in NOx ECs in fires across the globe. I compare mean ECs for fires in different locations but similar biomes (e.g. grasses) and find that while most ECs cover a relatively narrow range, ECs for several locations are significantly different from the mean biome EC. I examine seasonal variability in ECs, finding that ECs in African woody savannas have a strong seasonal dependence that is not observed in open savannas; this behavior may be related to reallocation of nitrogen to below ground during the fire season by plants and/or the seasonal variation of fire fuel composition in woody savannas. I also find that this behavior extends to other woody savanna regions in South America and Australia, and that ECs in several biomes exhibit a dependence on wind speed.

Main Content
Current View