Can Particle Mass Spectrometry Be Used to Measure Particulate Organic Nitrates?

Emily Bruns University of California
Veronique Perraud University of California
Alla Zelenyuk-Imre Pacific Northwest National Laboratory
Michael Ezell University of California
Stanley Johnson University of California
Yong Yu California Air Resources Board
Dan Imre Imre Consulting
Barbara Finlayson-Pitts University of California
Lizabeth Alexander Pacific Noerthwest National Laboratory

Category: Aerosol Properties

Working Group: Aerosol Life Cycle

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A typical FTIR spectrum of particles collected by impaction on ZnSe windows from the oxidation of biogenic organic precursors by NO3.

Elucidating the composition of aerosols in the atmosphere is essential to understanding the effects of anthropogenic and biogenic emissions on climate. Organic nitrates are an important class of compounds formed through the oxidation of organic compounds in the presence of NOx. Because many of the expected organic nitrate products are semi-volatile and multifunctional, they partition between the gas phase and particles, making identification and quantification more difficult. Particle analysis traditionally involves the collection of particles on filters followed by extraction and analysis by techniques such as FTIR and GC-MS. Although this provides specific composition and quantification information, it can introduce artifacts and does not provide real-time data. Particle mass spectrometry is one possibility for overcoming these issues; however, little is known about the response to organic nitrates. In this study, the response of a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) to particulate organic nitrate was investigated and compared to inorganic nitrate. FTIR spectroscopy on particles collected by impaction on ZnSe windows and single particle laser ablation mass spectrometry (SPLAT II) was carried out for comparison. Organic nitrates were formed from the NO3 radical reactions with α- and β-pinene, 3-carene, limonene, and isoprene, where products with sufficiently low vapor pressures form particles. Results from these studies will be presented to show that while all of these techniques have indicators for organic nitrates, identification of specific compounds in particles is not currently possible, and new approaches are needed. Currently under investigation is the application of atmospheric solids analysis probe mass spectrometry (ASAP-MS) to particulate organic nitrate analysis, for which preliminary results will be reported.

This poster will be displayed at ASR Science Team Meeting.