AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Response of HR-ToF-AMS to Inorganic Sulfates and Organosulfur Compounds and Applications in Field Measurements
YUNLE CHEN, Lu Xu, Elizabeth Stone, Timothy Humphry, Jurgita Ovadnevaite, Colin O’Dowd, Shan Huang, Laurent Poulain, Hartmut Herrmann, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 399 Working Group: Instrumentation and Methods
Abstract Organosulfur compounds are ubiquitous components of secondary organic aerosols (SOA), and have been identified in both laboratory-generated and ambient aerosols. Organosulfur compounds can play an important role in altering aerosol physicochemical properties, and are also thought to be good tracers for aqueous aerosol-phase SOA formation. High-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) has been widely used in aerosol studies, but the response of HR-ToF-AMS to organosulfur compounds is not well-understood. In HR-ToF-AMS, organosulfur compounds can fragment into both organic and sulfate fragments. Typically, the sulfate fragments are only interpreted as inorganic sulfates in subsequent analysis, even though they can arise from organosulfur compounds. This leads to uncertainties in the quantifications of organosulfur species and inorganic sulfate species, and the contribution of organosulfur compounds to total organic mass is underestimated. Here, we developed a new method to differentiate and quantify the signals from organic vs. inorganic sulfates in AMS measurements. Specifically, we investigated the mass spectra of different sulfate containing species, including ammonium sulfate, sodium sulfate and 16 different types of organosulfur compound standards. It is found that the sulfate mass spectra of organosulfur compounds are distinctively different from that of inorganic sulfates, with HSO3 (m/z 81) and H2SO4 (m/z 98) fragments showing the largest differences. While ammonium sulfate can produce both HSO3 and H2SO4 fragments, most organosulfur compounds cannot produce either fragment, except for methanesulfonic acid, which has a distinctively high HSO3 ion fraction. Making use of this difference, we can estimate organic sulfate concentration. This method is evaluated in the context of ambient measurements. For marine/coastal measurements, our method of sulfate apportionment provides a new perspective to estimate methanesulfonic acid concentration and evaluate the interactions between marine and anthropogenic aerosols. For inland measurements, it provides insights into sulfates originating from organic molecules.