Airborne measurements of aerosol extinction in the lower and middle troposphere over Wyoming, USA

Abstract

Particle size distributions, and scattering and absorption coefficients were measured over the Green River basin of Wyoming during the Southwest Wyoming Visibility Study (SWYVIS) in February and March 1996. Eleven flights were carried out, using the Wyoming King Air research aircraft. In the least polluted regions of the planetary boundary layer, particle number densities detected in the diameter range 0.13-3.0 mm were o100 cm À3 . Aloft, in the stable air of the free troposphere, they were generally even lower, often falling to a few tens of particles per cm 3 . Analyses of bulk aerosol filter samples showed that organic carbonaceous material was the dominant chemical component, with sulfate and refractory species being the largest inorganic components. Combining the filter data with separately measured black carbon mass loading values allowed refractive indices for the aerosol to be calculated, so that PCASP measured size distributions could be revised. Characterizing size parameters were obtained by fitting particle populations to bimodal lognormal distributions. Particle size distributions were somewhat broader at higher altitudes so that larger particles made greater contributions to extinction. Optical closure was attempted by comparing scattering and total extinctions computed by Mie theory with the corresponding values derived from the observations. While the calculated and measured single scattering albedo average values were in reasonably good agreement, even though individual pairs of values sometimes differed significantly, computed scattering coefficients often exceeded those derived from the measurements, by an average of 60%. Reasons for this discrepancy are explored, including the possible modification of the size distribution by partial or total volatilization of particles within the nephelometer and its inlet. r

Performance characteristics of the ultra high sensitivity aerosol spectrometer for particles between 55 and 800nm: Laboratory and field studies

“…Data gaps result from instrument down-time used for calibration and data archiving activities. In general, the observed concentration values are typical for unpolluted rural areas in the western USA, and are similar to those measured near the surface in remote areas of south-west Wyoming (Han, Montague, & Snider, 2003). The average total particle concentrations measured by the CPC and SMPS were 2200 ± 1500 cm −3 and 1700 ± 860 cm −3 , but occasionally concentration values were up to three times larger than the average for a few hours.…”

Aircraft measurements of the vertical distribution and activation property of aerosol particles over the Loess Plateau in China

“…The vertical distributions of aerosols such as the number concentration (N a ) and effective diameter (ED) have strong effects on estimates of direct and indirect radiative forcing by aerosols (IPCC, 2007). The observed aerosol properties such as vertical profiles of N a and ED vary with time, location, and atmospheric conditions (Welton et al, 2002;Han et al, 2003;O'Connor et al, 2008;Campbell et al, 2013;Li et al, 2013;Ma and Yu, 2014;Wang et al, 2014). Therefore, there is a need to better understand aerosol vertical distributions.…”

An empirical model of optical and radiative characteristics of the tropospheric aerosol over West Siberia in summer

“…Difficulty also arises from the fact that the available data from regular measurements of the vertical profiles of ω(λ, z) mainly refer to dry aerosol (Han et al, 2003;Andrews et al, 2011;McNaughton et al, 2011;Brock et al, 2011;Taubman et al, 2006;Magi et al, 2003). Only a few authors (e.g.,Öström and Noone, 2000; Magi et al, 2003Magi et al, , 2005Shinozuka et al, 2007) have attempted to simulate ω(λ, z) variations while considering changing aerosol parameters under the effect of the real relative humidity of air.…”

“…Data for regions over oceans were obtained during the experiments ACE-2 (Collins et al, 2000a;Öström and Noone, 2000), INDOEX (de Reuss et al, 2001) and ACE-Asia (Anderson et al, 2003;Redemann et al, 2003). More elaborate airborne datasets over coastal and continental locations have been acquired in the US mid-Atlantic coastal region (Hegg et al, 1997;Hartley et al, 2000), the Arctic McNaughton et al, 2011), North America (Collins et al, 2000b;Han et al, 2003;Magi et al, 2005;Shinozuka et al, 2007;Schwarz et al, 2006), Africa (Johnson et al, 2008;Magi et al, 2003) and Europe (Varotsos, 2005). Comparative analyses of the microphysical and optical parameters of some principal aerosol species (Saharan dust, biomass burning aerosol, European continental pollution, eastern seaboard USA pollution and clean maritime aerosol), obtained during international field campaigns, are presented in Osborne and Haywood (2005) and Clark and Kapustin (2010).…”

“…In some experiments, measurements of the optical characteristics were accompanied by determinations of the particle size distribution and chemical composition Osborn and Haywood, 2005;Han et al, 2003;Johnson et al, 2008;Collins et al, 2000a,b;Magi et al, 2005). These data were used for "optical closure" aimed at comparing the Mie scattering and extinction coefficients with the respective measured values.…”