AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Design, Characterization, and Application of a New Field-Portable Dual-Cell Multiwavelength Photoacoustic Spectrometer with Integrated Nephelometers
BENJAMIN SUMLIN, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 222 Working Group: Instrumentation and Methods
Abstract We present the development, calibration, and characterization of a new field-portable Multiwavelength Integrated Photoacoustic-Nephelometer (MIPN), an in situ, real-time, contact-free instrument designed primarily for field measurements of brown carbon (BrC).
The MIPN measures light absorption and scattering at four wavelengths (405, 488, 561, and 670 nm), and uses a dual-cell design with two independently-calibrated optoacoustic cavities, each equipped with scattering, absorption, and laser power detectors. This design allows the MIPN to circumvent errors introduced by combustion by-products such as NOX, which absorb strongly in the short visible and near-UV where BrC absorption is relevant. Typically, interfering gases are physically removed from sample streams physically with activated carbon denuders or are accounted for by frequently zeroing the instrument with aerosol-free baseline readings. Our dual-cell approach reduces all interfering phenomena (electrical and acoustic noise, absorbing gaseous species, etc.) to common-mode noise which is removed upon combining measurements. After optical analysis, the analyte is collected on a removable PTFE or quartz-fiber filter for offline analysis to further connect optical properties with physical properties (e.g., mass for mass absorption and mass scattering cross sections) and chemical properties (e.g., thermal desorption gas chromatography for molecular-level organic aerosol analysis).
We conclude with a discussion on deployment of the MIPN to the NASA/NOAA FIREX-AQ field campaign aboard the Aerodyne Mobile Laboratory, with a performance analysis and a first look at initial findings.