Evolution of Fresh Biomass Burning Aerosol Physical, Chemical, and Optical Properties upon Increase of Combustion Temperature
ZEZHEN CHENG, Valentina Sola, Gregory W. Vandergrift, Sijia Liu, Ryan Poland, Michael Caraway, Xena Mansoura, Schuyler Lockwood, Tania Gautam, Amna Ijaz, Yuzhi Chen, John Shilling, Nurun Nahar Lata, Payton Beeler, Laura Fierce, Gourihar Kulkarni, Alexander Laskin, Sergey Nizkorodov, Marwa El-Sayed, Geoffrey Smith, Rawad Saleh, Swarup China, ManishKumar Shrivastava, Alla Zelenyuk, Pacific Northwest National Laboratory
Abstract Number: 284
Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene
Abstract
Biomass burning aerosols (BBA) have important but poorly constrained impacts on Earth radiative forcing. This is partially because their complex physical, chemical, and optical properties are poorly understood due to the chaotic nature of combustion. Here, we conducted the first Study of Molecular, Optical, and Kinetic properties of combustion Emissions (SMOKE) Campaign at the Environmental Molecular Science Laboratory to systematically investigate the physical, chemical, and optical properties of BBA generated from pine needle combustion at 300 ºC, 400 ºC, 600 ºC, and 900 ºC with a constant air-to-fuel ratio. The size distribution of BBA decreases with the increase in combustion temperature, and that for 900 ºC emission shows an increase in the number fraction of particles larger than 500 nm. Mass absorption cross-section of BBA at 405 nm (MAC450) increases from 0.27 m2/g to 3.1 m2/g from 300 ºC to 600 ºC, but decreases to 0.12 m2/g at 900 ºC. Contrarily, absorption Ångström exponent decreases from 5.0 to 3.3 as combustion temperature increases from 300 ºC to 900 ºC, suggesting light-absorbing species might be more absorbing at higher combustion temperatures. The single particle mass spectrometer (miniSPLAT) analysis reveals a significantly higher intensity of inorganic species and char at 900 ºC BBA compared with other samples. The offline chemically resolved size distribution analysis confirms that these inorganic species dominate the large particle size for 900 ºC emission. This might explain the decrease of MAC450 at 900 ºC since these non- or weakly absorbing inorganics contribute to a significant fraction of total aerosol mass and can counterbalance the MAC450 of strongly absorptive species. Moreover, offline scanning electron microscopy analysis reveals an increase in organic particle viscosity with an increase in combustion temperature, and fresh tar balls and soot can be generated at 900 ºC.