Calibration of the Aerodyne Aerosol Mass Spectrometer with Total Particulate Nitrogen and Carbon Measurements

ANN M. MIDDLEBROOK, Derek J. Price, Allison Piasecki, Rishabh U. Shah, Katherine L. Hayden, James B. Burkholder, James M. Roberts, NOAA ESRL CSL

     Abstract Number: 127
     Working Group: Instrumentation and Methods

Abstract
The Aerodyne Aerosol Mass Spectrometer (AMS) and Aerosol Chemical Speciation Monitor (ACSM) instruments measure the real-time, non-refractory, chemical composition of aerosol particles and have been deployed by a multitude of institutions for ambient air measurements. Typical AMS and ACSM calibrations have relied on other well-calibrated aerosol instrumentation such as differential mobility analyzers with aerosol counting and optical sizing measurements to provide a precisely known mass concentration of aerosol species to compare with the AMS or ACSM instrument response. We have been developing new methods to measure aerosol nitrogen (N) and carbon (C) mass for direct verification of the AMS sensitivity to a variety of species pertinent to the atmosphere. These methods provide aerosol mass calibrations traceable to gas-phase standards: nitric oxide (NO) and carbon dioxide (CO₂). For this study, aerosol particles were generated, dried, size-selected, and then denuded before being introduced to the AMS and a heated platinum/molybdenum catalyst system. The catalysts converted aerosol nitrogen and carbon to NO and CO₂, that were subsequently detected with NO-ozone chemiluminescence and a commercial CO₂ analyzer. Elemental ratios were determined directly from these measurements. We also used a unit-mass-resolution AMS with a light-scattering module to measure the collection efficiency and a high-resolution AMS to distinguish elemental composition for direct comparisons with the catalyst-based conversion technique. Here we will present the results of experiments using aerosols composed of ammonium salts or molecules containing both carbon and nitrogen species.