Abstract
We examine the performance of our approach for calculating the total scattering coefficient of both non-absorbing and absorbing aerosol at ambient conditions from aircraft data. Our extended examination involves airborne in situ data collected by the U.S. Department of Energy’s (DOE) Gulf Stream 1 aircraft during winter over Cape Cod and the western North Atlantic Ocean as part of the Two-Column Aerosol Project (TCAP). The particle population represented by the winter dataset, in contrast with its summer counterpart, contains more hygroscopic particles and particles with an enhanced ability to absorb sunlight due to the larger fraction of black carbon. Moreover, the winter observations are characterized by more frequent clouds and a larger fraction of super-micron particles. We calculate model total scattering coefficient at ambient conditions using size spectra measured by optical particle counters (OPCs) and ambient complex refractive index (RI) estimated from measured chemical composition and relative humidity (RH). We demonstrate that reasonable agreement (~20% on average) between the observed and calculated scattering can be obtained under subsaturated ambient conditions (RH < 80%) by applying both screening for clouds and chemical composition data for the RI-based correction of the OPC-derived size spectra.
Highlights
There is an increasing demand to better understand the role of atmospheric aerosol in the Earth’s radiation budget over a range of seasons [1,2]
We use an integrated dataset collected by the Department of Energy (DOE) Gulfstream 1 (G-1) aircraft during the winter of 2013 as part of the Two-Column Aerosol Project
This dataset includes: (1) size distributions measured by three optical particle counters (OPCs): an ultra-high sensitivity aerosol spectrometer (UHSAS; particle size range 0.06–1 μm), a passive cavity aerosol spectrometer (PCASP; particle size range 0.1–3 μm), and a cloud and aerosol spectrometer (CAS; particle size range 0.6–10 μm) mounted on the G-1; (2) chemical composition data measured by three instruments: an aerosol mass spectrometer (AMS; particle size range 0.06–0.6 μm)
Summary
There is an increasing demand to better understand the role of atmospheric aerosol in the Earth’s radiation budget over a range of seasons [1,2]. It should be emphasized that the miniSPLAT measures organic particles, sea salt, dust, and soot particles—were observed by miniSPLAT during the composition of individual particles (both refractory and nonrefractory), while the AMS provides flight Some of these particle types exhibit large variations for different FLs. Most noticeable, sea salt information on bulk composition associated with nonrefractory aerosol. The ground-based meteorological measurements of thermodynamic structure of atmosphere demonstrate that about 1-km convective boundary layer is typical for winter, associated with relatively cold continental air moving over relatively warm Atlantic Ocean [11] These combined in situ and meteorological measurements suggest that the relative contribution of the sea salt to the total mass loading could be substantial for several winter FLs, those flown at low altitude. We discuss the potential impact of sea salt on our results
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