Airborne Aerosol in Situ Measurements during TCAP: A Closure Study of Total Scattering
Berg, Larry K.
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We present a framework for calculating the total scattering of both non-absorbing and absorbing aerosol at ambient conditions from aircraft data. Our framework is developed emphasizing the explicit use of 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 scattering is demonstrated using three types of data collected by the U.S. Department of Energy’s (DOE) aircraft during the Two-Column Aerosol Project (TCAP). Namely, these data types are: (1) size distributions measured by a suite of OPC’s; (2) chemical composition data measured by an Aerosol Mass Spectrometer and a Single Particle Soot Photometer; and (3) the dry total scattering coefficient measured by a integrating nephelometer and scattering enhancement factor measured with a humidification system. We demonstrate that good agreement (~10%) between the observed and calculated scattering can be obtained under ambient conditions (RH < 80%) by applying chemical composition data for the RI-based correction of the OPC-derived size spectra. We also demonstrate that ignoring the RI-based correction or using non-representative RI values can cause a substantial underestimation (~40%) or overestimation (~35%) of the calculated scattering, respectively.
SubjectAerosol Mass Spectrometer (AMS)
aircraft measurements of aerosol microphysical
and optical components and ambient relative humidity
Cloud and Aerosol Spectrometer (CAS)
Passive Cavity Aerosol Spectrometer (PCASP)
Single Particle Soot Photometer (SP2)
Two-Column Aerosol Project (TCAP)
Ultra-High Sensitivity Aerosol Spectrometer (UHSAS)
Except where otherwise noted, this item's license is described as Creative Commons Attribution 4.0 United States
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