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Advancing measurements of organic aerosols under atmospherically relevant aerosol mass loadings

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Monday, October 24, 2011, 4 pm

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Giuseppe Petrucci
University of Vermont

Atmospheric aerosols are at the nexus of atmospheric processes impacting radiative energy balance, visibility, regulation of reactive gases, and human health, to name a few. A major fraction of atmospheric aerosols contains significant amounts of organic matter, which is directly emitted to the atmosphere or, arguably more importantly, formed in the atmosphere through oxidative reactions of volatile organic compound (VOC) precursors. This latter class of organic aerosol (OA) is generally termed secondary organic aerosol (SOA) and has been a focus of extensive research efforts in the past decade. Aerosol mass spectrometry (AMS) is an innovative class of instruments that has been transformative in our understanding of the sources, chemistry and atmospheric aging of OA. AMS has been employed in field campaigns and laboratory studies to gain an improved, and at times nascent understanding of organic aerosols from the molecular scale to regional and global impacts. In this presentation, a brief overview of the on-line organic aerosol analysis will be given, followed by a more in depth discussion of soft ionization based AMS methodologies, which give unique insights into the chemical composition of nonrefractory components of submicron aerosols, including the organic fraction. Specifically, a new soft ionization AMS method will be presented, near-infrared laser desorption/ionization AMS (NIR-LDI-AMS), which has demonstrated unprecedented sensitivity for components associated with primary and secondary organic aerosols (POA and SOA, respectively). Notably, the limit of detection for oleic acid, a ubiquitous component of POA, was determined to be 140 fg of sampled aerosol mass. Other organic components commonly associated with POA and SOA have limits of detection ranging from 89 fg for pinic acid to 8.8 pg for cholesterol. NIR-LDI-AMS was coupled to the University of Vermont Environmental Chamber to measure the evolution of components of SOA for a variety of VOC precursors, including α-pinene, limonene and isoprene, at atmospherically relevant organic aerosol mass loadings (COA) from 1.5 to 25.0 μg m-3. The composition of biogenic SOA and compositional variability as a function of COA and time as elucidated by NIR-LDI-AMS will be presented. These measurements represent a significant advancement to atmospheric science because most current AMS measurements of SOA in chamber-based studies have been conducted at COA > 15 μg m-3, while atmospheric levels are often less than 10 μg m-3. This advancement will translate to more accurate predictions of SOA fluxes from bottom-up models that incorporate data derived from laboratory-based measurements. Finally, the viability of employing NIR-LDI-AMS for field measurements of POA and SOA are will be discussed.

Host Lynn Mazzoleni


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