Quantifying Carbon Monoxide Emissions on the Scale of Large Wildfires

Abstract

The October 2017 fires near Santa Rosa in northern California (N. CA) were the second most destructive fires to date in California 12 , killing 44 people 13 , destroying nearly 9,000 structures 13,14 , with reported losses of over $10 billion 14 , and resulting in the highest particulate matter (PM2.5) levels recorded in the Bay Area since 1999 15 . The Tubbs fire, the largest of the Oct. 2017 N. CA fires, which devastated the city of Santa Rosa, was started by a private electrical system 16 , and was associated with an intense terrain-induced downslope windstorm 17 . Such windstorms, commonly known as "Santa Ana" or "Diablo" winds, can be very destructive when driving fires and are projected with climate change to extend the fire season later into the fall and winter 17 .The Oct. 2017 N. CA fires are an example of fires with anthropogenic ignition sources and their subsequent air quality impacts that are likely to increase due to a warmer and drier climate in the Western U.S. during the 21 st century 18,19,20,21 . These trends combined with rising numbers of humans living in the urban-wildland interface are likely to result in increases in population exposure to fire activity 22 and poor air quality episodes 23 . Long-term exposure to elevated PM2.5 may increase human susceptibility to respiratory diseases such as coronavirus (COVID-19) 24,25 .The University of Colorado Airborne Solar Occultation Flux (CU AirSOF) instrument was deployed to quantify the emission fluxes of the N. CA wildfires on Oct. 10, 2017. CU AirSOF consists of a Fourier Transform Spectrometer installed on a research aircraft, and uses a digital fast solar tracker to point directly at the sun to measure the total CO column above the aircraft at mid-infrared wavelengths 26,27 . The SOF method has been used to quantify emissions from area sources by mass balance 28,29,30 , but its potential to study wildfires remains largely unexplored. The CU AirSOF instrument is a unique prototype, and optimized to quantify wildfire emissions due to

Carbon Monoxide in Optically Thick Wildfire Smoke: Evaluating TROPOMI Using CU Airborne SOF Column Observations

“…Section describes active measures taken in this study to deal with the fundamental sampling challenge in time and space, and introduces case studies and radiative transfer simulation tools used to assess the (multispectral) effects of aerosols in thick wildfire smoke. Section aims to better understand the accuracy of CO column enhancements to better quantify wildfire emissions (e.g., Bela et al; Burling et al; Kille et al; Volkamer et al) and assess the uncertainties due to aerosols in optically thick smoke plumes. The results from the measurement comparisons are explored in Sections –3.4, followed by an error budget, bias assessment in thick wildfire smoke, radiative transfer simulations to assess the effects of aerosols in thick wildfire smoke at different wavelengths, and Section .…”

Airborne Emission Rate Measurements Validate Remote Sensing Observations and Emission Inventories of Western U.S. Wildfires

“…45 The emissions derived from both burned area (bottom-up) and FRP-based (top-down) methods can differ by an order of magnitude and are challenging to validate because of limited ground-based and in situ observations. 18,19,24,42,44 Emission rates (g s −1 ), the mass of a compound released per unit time, estimated from observations typically require knowledge of the entire plume structure. Aircraft sampling of emission plumes generally only characterizes the horizontal cross section of the plume, whereas the vertical distribution of species is typically unknown or approximated.…”

The CU Airborne Solar Occultation Flux Instrument: Performance Evaluation during BB-FLUX

“…Biomass burning is an important source of a variety of atmospheric trace gases. , The emissions from biomass burning, which includes wildfires in the western United States (U.S.), impact ecosystems, air quality, and human health (e.g., Chen et al or Reid et al). Uncertainties and discrepancies in emission inventories can have substantial impact on the conclusions drawn about the impacts fires have on air quality and climate (e.g., Carter et al or Bela et al). It therefore is increasingly important in the changing Earth system to be able to accurately quantify biomass burning emissions .…”