Abstract Number: 311 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Biomass burning is the largest contributor of soot and organic aerosols in the atmosphere and significantly affects Earth’s radiation budget and climate. We analyzed ~10,000 single particles from two of the largest wildfires in New Mexico’s history using electron microscopy coupled with energy dispersive X-ray spectroscopy. The samples include fresh smoke from the Las Conchas fire (2011) and relatively aged (~ 7 hours) smoke from the Whitewater Baldy Complex fire (2012) collected at Los Alamos National Laboratory. Effects of particle coatings were probed by using thermo-denuder before particle collection and making real time measurements of soot mass and mixing state with a single particle soot photometer.
Tar balls were the most abundant particles (~80% in fresh smoke and ~56% in aged smoke). In addition, in the aged smoke we observed 27% of aggregates mostly consist of large, nearly spherical particles, possibly of organic matter and a small fraction of tar balls. Detailed analysis of those aggregates showed that they contain between 2 to 44 individual particles. Relative abundance of soot particles was found to be the same (~8%) for both fresh and aged smoke. However, their mixing states are significantly different. To this end we classified and quantified them into four categories: bare (no visual coating), partly-coated, and soot-inclusions, where soot particles is not uniformly coated, embedded (heavily-coated). We found that the fraction of soot-inclusion particles were 12% and 30% for fresh and aged smoke, respectively, indicating that the residence time in the atmosphere influences these complex mixings. The fractal dimension of ambient soot decreased significantly upon removal of coatings via thermo-denuding. These findings can guide the development of new parameterizations to improve the performances of numerical models for the simulation of aerosol mixing, morphology and optical properties.