Aerosol optical properties of smoke from the Las Conchas wildfire, Los Alamos, New Mexico
Poster PDF
Authors
Kyle Gorkowski — Los Alamos National Laboratory
Manvendra K. Dubey — Los Alamos National Laboratory
Allison C Aiken — Los Alamos National Laboratory
Bradley Flowers — Los Alamos National Laboratory
Benjamin Klein — Los Alamos National Laboratory
Claudio Mazzoleni — Michigan Technological University
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China Swarup — Michigan Technological University
Category
Aerosol Properties
Description
The Las Conchas wildfire in northern New Mexico started on June 26, 2011 and spread rapidly, eventually burning an area of 634 square kilometers (245 square miles). Due to the close proximity to the fire, the Los Alamos National Laboratory (LANL) was shut down and the town evacuated for several days. Immediately after LANL reopened (July 7, 2011) the Earth and Environmental Sciences Division (EES-14) attained unique measurements of the smoke by sampling the ambient air. Three Integrated Photoacoustic/Nephelometer Spectrometers (DMT Inc.) were set up to measure aerosol light absorption and scattering coefficients. A University of Northwest Switzerland thermodenuder was used to remove compounds that are volatile at temperatures up to 200C. The aerosol’s optical properties were measured before and after denuding the sample at 405nm (blue), 532nm (green), 781nm (red), and for non-denuded particles also at 375nm (ultraviolet). The aerosol size distributions were measured after the denuder with a Laser Aerosol Spectrometer (LAS, TSI Inc.) and black carbon was measured with a Single Particle Soot Photometer (SP2, DMT Inc.). These measurements are used in conjunction with numerical simulations to determine the bulk optical properties of the aerosol.
Aerosols in wildfire smoke are composed of organic and black carbon (soot) particles that are formed during wood combustion and pyrolysis. The optical properties of the smoke particles are complex and lead to large uncertainties in assessing the global climate. During the measurement period, the Las Conchas fire provided very high particle concentrations (up to 200 μg/m3) that were exploited to investigate their optical properties. By heating the particles to temperatures ranging from 75 to 200C in the denuder, volatile organics were removed and the optical properties of the remaining particles were measured. Denuding of the aerosols removed the outer organic coatings, leaving behind the inner core of black carbon (soot) and any compounds that did not volatize completely. By simultaneously measuring the optical properties of the non-denuded as well as the denuded aerosol, we can study how the coatings affect the optical properties. The absorption coefficient measurements showed that coatings can cause an increase or decrease in absorption.
