Airborne Aerosol in Situ Measurements during TCAP: A Closure Study of Total Scattering

Journal Article · Fri Jul 31 00:00:00 EDT 2015 · Atmosphere (Basel)

DOI: https://doi.org/10.3390/atmos6081069 · OSTI ID:1209863

Kassianov, Evgueni I. ^[1]; Berg, Larry K. ^[1]; Pekour, Mikhail S. ^[1]; Flynn, Connor J. ^[1]; Tomlinson, Jason M. ^[1]; Chand, Duli ^[1]; Shilling, John E. ^[1]; Ovchinnikov, Mikhail ^[1]; Barnard, James C. ^[2]; Sedlacek, Art ^[3]; Schmid, Beat ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. University of Nevada, Reno, NV (United States)
3. Brookhaven National Laboratory, Upton, NY (United States)

We present here a framework for calculating the total scattering of both non-absorbing and absorbing aerosol at ambient conditions from aircraft data. The synergistically employed aircraft data involve aerosol microphysical, chemical, and optical components and ambient relative humidity measurements. Our framework is developed emphasizing the explicit use of the complementary chemical composition data for estimating the complex refractive index (RI) of particles, and thus obtaining improved ambient size spectra derived from Optical Particle Counter (OPC) measurements. The feasibility of our framework for improved calculations of total aerosol scattering is demonstrated for different ambient conditions with a wide range of relative humidities (from 5 to 80%) using three types of data collected by the U.S. Department of Energy (DOE) G-1 aircraft during the recent Two-Column Aerosol Project (TCAP). Namely, these three types of data employed are: (1) size distributions measured by an Ultra High Sensitivity Aerosol Spectrometer (UHSAS; 0.06-1 µm), a Passive Cavity Aerosol Spectrometer (PCASP; 0.1-3 µm) and a Cloud and Aerosol Spectrometer (CAS; 0.6- >10 µm), (2) chemical composition data measured by an Aerosol Mass Spectrometer (AMS; 0.06-0.6 µm) and a Single Particle Soot Photometer (SP2; 0.06-0.6 µm), and (3) the dry total scattering coefficient measured by a TSI integrating nephelometer at three wavelengths (0.45, 0.55, 0.7 µm) and scattering enhancement factor measured with a humidification system at three RHs (near 45%, 65% and 90%) at a single wavelength (0.525 µm). We demonstrate that good agreement (~10% on average) between the observed and calculated scattering at these three wavelengths can be obtained using the best available chemical composition data for the RI-based correction of the OPC-derived size spectra. We also demonstrate that ignoring the RI-based correction and using non-representative RI values can cause a substantial underestimation (~40% on average) and overestimation (~35% on average) of the calculated total scattering, respectively.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1209863
• Report Number(s): PNNL-SA-110601; KP1701000
• Journal Information: Atmosphere (Basel), Journal Name: Atmosphere (Basel) Journal Issue: 8 Vol. 6; ISSN 2073-4433; ISSN ATMOCZ
• Publisher: MDPICopyright Statement
• Country of Publication: United States
• Language: English