Kelley Barsanti - Biogenic Secondary Organic Aerosol Formation.
The main constituents of atmospheric aerosols are sulfates, nitrates, crustal material, elemental carbon, and organic carbon. While the inorganic fractions are relatively well characterized, the organic fraction remains poorly understood. The composition of atmospheric aerosols affects their hygroscopicity, ability to act as cloud condensation nuclei, optical properties, and role in climate forcing. Therefore, in order to understand the extent of such effects on regional as well as global scales, models that accurately represent the organic component of atmospheric aerosols are needed.
The ability to accurately represent the organic component of atmospheric aerosols is limited by our understanding of the formation and evolution of secondary organic aerosol (SOA). SOA comprises a significant, if not dominant, fraction of total organic aerosol sampled in rural and urban environments. My research focuses on using chamber experiments and process-level models to improve our understanding of SOA formation and evolution (e.g., growth, oxidation, and other processes which may increase or decrease levels of SOA, and/or change the chemical and physical properties of SOA). The ultimate goal of this research is to use the knowledge gained from these experiments and process-level models to improve the representation of organic aerosols in regional and global air quality and climate models.
Shown in Fig. 1 is the Biosphere-Atmosphere Interactions Chamber currently under construction at NCAR. This 10 m3 chamber will allow us to investigate SOA formed by volatile organic compound (VOC) emissions from live trees. Biogenic VOCs are thought to be the major precursors of SOA on a global scale, though their contribution has not been fully characterized. On a regional scale, estimating the contribution of biogenic VOCs to SOA is further complicated by the interactions between biogenic and anthropogenic VOCs and SOA constituents. For example, of recent interest is whether or not sulfuric acid (typically formed from anthropogenic emissions of SO2) is required for biogenic VOCs to form stable nuclei and grow into measureable particles. The Biosphere-Atmosphere Interactions chamber will provide an unparalleled opportunity to investigate uncertainties such as the one above, as well as others related to biogenic SOA formation and evolution.
Figure 1: Biosphere-Atmosphere Interactions Chamber
ASP Spotlight July 2007
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