Carbonaceous aerosols are prevalent in urban areas and affect the radiative balance of the Earth by absorbing and scattering light. Carbonaceous aerosol is composed of black carbon (BC) and various types of organic carbon (OC). It is well known that BC is the most absorbing aerosol in the atmosphere. Although the role of OC in light absorption has not been thoroughly investigated, some organic compounds also have significant absorption, which is greater at near-ultraviolet and blue wavelengths. Since visible absorption is far more important for the energy balance than ultraviolet absorption, to the extent that OC absorbs visible light, it may be a non-negligible contributor to direct aerosol radiative forcing. In this work, we examine primary BC and OC emitted from solid fuels, which provide about two-thirds of global primary organic aerosol emissions. Our work focuses on understanding the chemical composition and optical properties of these particles in order to better characterize them in models. Samples were generated in a laboratory combustion chamber at different burning conditions using softwood and hardwood, and collected on baked quartz filters. The filters were then extracted with deionized water and different organic solvents, including methanol, hexane and acetone. Light absorption of different sample solutions was tested at the wavelength from 190nm to 800nm. Absorption spectra of the extracts were measured with a Shimadzu UV-2401 UV-Vis recording spectrophotometer. Total carbon was measured with a Sunset OC/EC analyzer. Preliminary results showed that light absorption in visible spectrum was partially caused by water soluble organic carbon and another larger portion was caused by water insoluble organic carbon. The greatest absorption was that of acetone extracts, followed by that of methanol, hexane and water extracts. This suggests that chromophores are associated with compounds that are neither completely polar nor completely non-polar. In addition, high performance liquid chromatography (HPLC) combined with ultraviolet-visible spectroscopy identified the polarity of molecules associated with visible and near-ultraviolet absorption in the water-soluble fraction. We report relationships between these chemical analyses and climate-relevant aerosol properties, including total absorption per mass, absorption Angstrom exponent, and hygroscopicity.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 0305 Aerosols and particles (0345;