A Closure Study of Aerosol Total Scattering from Airborne In situ Measurements under Challenging Observational Conditions

 
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Authors

Evgueni Kassianov — Pacific Northwest National Laboratory
Mikhail S. Pekour — Pacific Northwest National Laboratory
Larry Berg — Pacific Northwest National Laboratory
James Barnard — University of Nevada Reno
Duli Chand — Pacific Northwest National Laboratory
Connor J. Flynn — University of Oklahoma School of Meteorology
Jennifer M. Comstock — Pacific Northwest National Laboratory
Arthur J Sedlacek — Brookhaven National Laboratory
John E Shilling — Pacific Northwest National Laboratory
Hagen Telg — Cooperative Institute for Research in Environmental Sciences
Jason Tomlinson — Pacific Northwest National Laboratory
Alla Zelenyuk-Imre — Pacific Northwest National Laboratory
Jacqueline Mary Wilson — Pacific Northwest National Laboratory
Jerome D Fast — Pacific Northwest National Laboratory

Category

General topics – Aerosols

Description

The compact and multi-variable measurement system used onboard the DOE Gulfstream 1 (G-1) aircraft includes several instruments for in situ measurements of aerosol and cloud properties. Since these airborne instruments have different design and sensitivities to particle size, successful data integration represents a difficult task. Typically, a special kind of quantitative comparison experiment – traditionally referred to as a closure study – is performed to assess the consistency and reasonableness of integrated aerosol data. Previously, we have successfully performed a closure study of ambient aerosol total scattering coefficient using Two-Column Aerosol Project (TCAP) summer data collected by the G-1 aircraft. In comparison with summer, winter represents more challenging observational conditions for the closure study because of: (1) frequent cloudy occurrences, which increase strongly the variability of the observed scattering coefficient, and (2) an enhanced fraction of super-micron aerosol particles, which have often been ignored in the closure studies due to limited information on their chemical composition. These challenging conditions call into question our ability to accomplish successfully a closure study. We will present an integrated winter dataset in the context of a traditional closure experiment. Our integrated dataset includes: (1) size distributions measured by three Optical Particle Counters (OPCs): an Ultra-High Sensitivity Aerosol Spectrometer (UHSAS), a Passive Cavity Aerosol Spectrometer (PCASP) and a Cloud and Aerosol Spectrometer (CAS); (2) chemical composition data measured by three instruments: an Aerosol Mass Spectrometer (AMS), a Single Particle Soot Photometer (SP2), and single particle mass spectrometer (miniSPLAT); and (3) the dry total scattering coefficient measured by TSI integrating nephelometer and f(RH) measured with a humidification system. We also discuss the major assumptions and related corrections that are the most critical for performing the closure study. For example, we demonstrate that a reasonable level of agreement (about 15% on average) between the observed and calculated values of the ambient total scattering coefficient can be achieved -- even under the challenging wintertime conditions -- if information on the measured chemical composition is applied to correct the OPC-derived size spectra. Finally, we highlight the value of the integrated airborne dataset for the evaluation of model predictions.