Environmental Molecular Sciences Laboratory

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Chemical Characterization of Atmospheric Aerosols and Cloud Water using High-Resolution Mass Spectrometry and Single-Particle

Tuesday, October 1, 2013
Principal Investigator: 
Kerri Pratt
Lead Institution: 
University of Michigan
Closed Date: 
Saturday, October 31, 2015
Project ID: 

High-resolution tandem mass spectrometry and single particle microscopy analysis will be utilized to determine the organic molecular composition and size-dependent mixing state of atmospheric aerosols and cloud water collected near forested areas downwind of urban areas. For year 1 of the project, aerosol and cloud water samples will be collected during the multi-institution Southern Oxidant and Aerosol Study (SOAS) in the southeastern U.S. from June-July 2013. Cloud water samples will be collected aboard the Purdue University Airborne Laboratory for Atmospheric Research (ALAR). Aerosol filter samples will be collected at the ground site in Centreville, AL, as well as aboard ALAR. The organic molecular composition will be determined using high-resolution mass spectrometry interfaced with a nanospray desorption electrospray ionization (nano-DESI) source and ultra-performance liquid chromatography (UPLC) separation stage and electrospray ionization. At the single particle level, computer controlled scanning electron microscopy (CCSEM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) will be combined to determine the distribution of sulfur-containing species as a function of particle size and chemistry. We will test the hypothesis that organosulfates are common aerosol and cloud water constituents via both high and low NOx formation pathways involving organic nitrates and epoxides, respectively. To connect these pathways, the atmospheric chemistry of organic nitrates and secondary organic aerosol (SOA) will be simulated via one-dimensional and CMAQ modeling. In addition, gas-phase organic nitrates will be measured during SOAS and will aid interpretation of the organic aerosol molecular composition determined in the proposed study. SOA formation pathways and aqueous-phase processing will be investigated through comparison of the chemistry of aerosol and cloud water samples. The information gained from the proposed analyses will be utilized to improve the parameterization of SOA formation in the CMAQ model. Overall, the proposed project will improve our understanding of the production, fate, and chemical composition of atmospheric aerosols formed from the oxidation of biogenic volatile organic compounds. These chemically complex atmospheric aerosols are formed via interactions between natural and urban trace gas emissions and significantly impact air quality, cloud formation and properties, and the Earth's biogeochemical cycles. Therefore, the proposed analyses of aerosol and cloud water samples will improve our understanding of biogenic-anthropogenic interactions, SOA formation, and aqueous SOA processes. The unique mass spectrometry and microscopy measurement capabilities, available at EMSL with the leading researchers in the use of this instrumentation for aerosol analysis, are paramount to the success of the proposed project. In particular, the nano-DESI technique was developed at EMSL and will be a primary focus of the aerosol analyses using the high-resolution mass spectrometry capability (specifically, LTQ-Orbitrap and 6T FTICR mass spectrometers) available at EMSL. These techniques are required to determine the molecular composition, including structural information, of the high molecular weight organic compounds in the SOA and cloud water. Likewise, single-particle analysis via CCSEM and TOF-SIMS, needed to determine sulfur speciation as a function of particle size and chemistry, would also only be possible through the proposed EMSL collaboration.