Aerosol single scattering albedo retrieved from measurements of surface UV irradiance and a radiative transfer model

Abstract

[1] Aerosol single scattering albedo (w), the ratio of aerosol scattering coefficient to total aerosol extinction coefficient, at UV wavelengths is an important aerosol radiative parameter in determining surface UV irradiance. Surface measurements of total and diffuse UV irradiance in the summer and fall of 1999 at the seven narrowband wavelength channels of an UV multifilter rotating shadowband radiometer (UVMFR-SR) at Black Mountain, N. C., were coupled with a tropospheric ultraviolet radiative transfer model to produce values of w. Its value ranged from 0.65 to 0.91 at 300 nm, 0.71 to 0.96 at 305.5 nm, 0.73 to 0.97 at 311.4 nm, 0.74 to 0.91 at 317.6 nm, 0.76 to 0.96 at 325.4 nm, 0.77 to 0.97 at 332.4 nm, and 0.80 to 0.99 at 368 nm. Error in this procedure decreases with increasing aerosol optical depth (AOD), from ±0.63 at AOD = 0.05 to ±0.04 at AOD = 1.0 averaged over the seven wavelengths. The current values of w have a slightly wider variation than values reported from a previous study at the same site. The lower values of w could indicate that, over the site, preferential absorption of UV radiation by black carbon aerosols could be occurring. More values of w in the UV spectrum will allow for better estimation of this parameter for UV radiative transfer modeling and will lessen error in estimation of surface UV irradiances.

Spectral absorption of biomass burning aerosol determined from retrieved single scattering albedo during ARCTAS

“…This ultimately makes identifying variability due to aerosol scattering and/or absorption using actinic flux much more difficult than irradiance. As a result, irradiance has been the preferred radiation measurement in previous SSA and AAE retrievals (e.g., Petters et al, 2003;Krotkov et al, 2005b;Corr et al, 2009;Buchard et al, 2011). However, as actinic flux is used to quantify the rate of many atmospheric photochemical reactions, being able to use it in aerosol retrievals would allow for the direct determination of aerosol impacts on photochemistry.…”

“…However, measurements of SSA have been largely limited to the visible due to few scattering and absorption measurements at UV wavelengths. Recent studies have thus relied on the retrieval of UV SSA values from radiation measurements (e.g., Petters et al, 2003;Krotkov et al, 2005b;Barnard et al, 2008;Corr et al, 2009;Buchard et al, 2011). In addition to including values at UV wavelengths, SSA retrieved from radiation measurements often has a high spectral resolution making it possible to determine AAE calculations from multiple wavelength exponential fits.…”

“…This highlights the difficulty of using actinic flux in aerosol optical properties retrievals. Many retrievals to date have relied on irradiance data (e.g., Petters et al, 2003;Krotkov et al, 2005b;Corr et al, 2009;Buchard et al, 2011) which are much more sensitive to changes in the radiation field due to clouds, aerosol, surface albedo, and gases. To assess errors associated with actinic flux-based retrievals, results from such retrievals should be compared to those performed using co-located irradiance data.…”

“…Retrievals have been performed using both irradiance (the radiation incident on a plane expressed in W m −2 ) as well as actinic flux (radiation to a point) (e.g., Petters et al, 2003;Krotkov et al, 2005bKrotkov et al, , 2011Barnard et al, 2008;Corr et al, 2009;Buchard et al, 2011). Unlike irradiance, actinic flux does not account for photon direction or "source" (e.g., direct from the sun or scattered from the atmosphere and/or surface).…”

Quantifying the single scattering albedo for the January 2017 Chile wildfires from simulations of the OMI absorbing aerosol index

“…As a result, ω 0 is usually retrieved by forward simulations that are adapted to observational parameters. Many implementations have been done for ground-based network measurements (Dubovik et al, 1998;Eck et al, 2003;Petters et al, 2003;Kassianov et al, 2005;Corr et al, 2009;Yin et al, 2015), while relatively fewer applications to satellite instruments exist due to lack of validation (Lee et al, 2007;Ialongo et al, 2010;Eck et al, 2013). Moreover, a majority of those methods heavily depend on the aerosol optical thickness (τ), either 50 in forward model simulations or in validation procedures.…”