Strong Wavelength Dependence of Aerosol Light Absorption from Peat Combustion

Friday, 19 December 2014
Madhu S Gyawali1, Rajan K. Chakrabarty2, Reddy L. N. Yatavelli3, L.W. Antony Chen3, Joseph Knue1, Vera Samburova1, Adam Watts1, Hans Moosmüller3, William P Arnott4, Xiaoliang Wang3, Barbara Zielinska1, Judith C. Chow3, John G. Watson3 and Anna Tsibart5, (1)Desert Research Institute Reno, Reno, NV, United States, (2)Washington University in St Louis, St. Louis, MO, United States, (3)Desert Research Institute, Reno, NV, United States, (4)University of Nevada Reno, Reno, NV, United States, (5)Moscow State Lomonosov University, Moscow, Russia
Globally, organic soils and peats may store as much as 600 Gt of terrestrial carbon, representing 20 – 30% of the planet’s terrestrial organic carbon mass. This is approximately the same carbon mass as that contained in Earth’s atmosphere, despite peatlands occupying only 3% of its surface. Effects of fires in these ecosystems are of global concern due to their potential for enormous carbon release into the atmosphere. The implications for contributions of peat fires to the global carbon cycle and radiative forcing scenarios are significant. Combustion of peat mostly takes place in the low temperature, smoldering phase of a fire. It consumes carbon that may have accumulated over a period of hundreds to thousands of years. In comparison, combustion of aboveground biomass fuels releases carbon that has accumulated much more recently, generally over a period of years or decades. Here, we report our findings on characterization of emissions from laboratory combustion of peat soils from three locations representing the biomes in which these soils occur. Peat samples from Alaska and Florida (USA) and Siberia (Russia) were burned at two different fuel moisture levels. Burns were conducted in an 8-m3 volume combustion chamber located at the Desert Research Institute, Reno, NV, USA. We report significant brown carbon production from combustion of all three peat soils. We used a multispectral (405, 532, 781 nm) photoacoustic instrument equipped with integrating nephelometer to measure the wavelength-dependent aerosol light absorption and scattering. Absorption Ångström exponents (between 405 and 532 nm) as high as ten were observed, revealing strongly enhanced aerosol light absorption in the violet and blue wavelengths. Single scattering albedos (SSA) of 0.94 and 0.99 were observed at 405 and 532 nm, respectively, for the same sample. Variability of these optical parameters will be discussed as a function of fuel and combustion conditions. Other real-time measurements included CO2, CO, NOx (NO and NO2), and SO2 concentrations, PM size-distributions, and PM and black carbon mass concentrations. In addition, Teflon-membrane, quartz-fiber, and Teflon-impregnated glass fiber (TIGF) filters followed by XAD-4 cartridges were collected for detailed chemical analysis.