Determination of aerosol properties from MAX-DOAS observations of the Ring effect

Abstract

Abstract. The first quantitative comparison of MAX-DOAS observations of the Ring effect with model simulations is presented. It is performed for a large variety of viewing geometries (solar zenith angles: 45 • to 90 • , elevation angles: 3 • , 6 • , 10 • , 18 • , 90 • ; three different azimuth angles), which allows a comprehensive test of our capabilities to measure and simulate the Ring effect. In addition to the Ring effect, also the observed O 4 absorptions (optical densities) and radiances are compared with model simulations. In general good agreement is found for all measured quantities. From several sensitivity studies it is found that for most measurement situations, the aerosol optical depth has usually the strongest influence on the observed quantities, but also other aerosol properties like e.g. the vertical distribution have a significant effect. In some aspects, the qualitative dependence of the Ring effect on aerosol properties is similar to that of the O 4 absorption. This can be understood, since both quantities depend strongly on the light path length in the lower atmosphere. However, since the Ring effect depends also on the properties of the scattering processes, in specific cases observation of the Ring effect can provide complementary information to that retrieved from the O 4 observations. This is e.g. possible for measurements at small relative azimuth angles, from which information on the aerosol phase function can be derived. Observations at large solar zenith angle might allow the retrieval of stratospheric aerosol properties, even in cases with very low aerosol optical depths. In addition, Ring effect observations in zenith direction are rather sensitive to the aerosol optical depth (in contrast to O 4 observations), which might allow to retrieve information on aerosol properties from existing zenith UV data sets prior to the MAX-DOAS era.

The CU ground MAX-DOAS instrument: characterization of RMS noise limitations and first measurements near Pensacola, FL of BrO, IO, and CHOCHO

“…Vibrational Raman scattering has been suggested to play a role for zenith sky DOAS measurements of stratospheric absorbers at high SZA (Platt et al, 1997), as well as for liquid water in the oceans (Vountas et al, 2003). Vibrational Raman scattering on gas-phase molecules is today not typically considered in the analysis of MAX-DOAS spectra, which treat only the rotational component of Raman scattering to calculate the Ring reference spectrum (Chance and Spurr, 1997;Vountas et al, 1998;Platt and Stutz, 2008;Wagner et al, 2009). We are unaware of a discussion of vibrational Raman scattering by gas-phase molecules for tropospheric absorbers measured by MAX-DOAS, where in addition to N 2 and O 2 also H 2 O could play a role.…”

Eight-component retrievals from ground-based MAX-DOAS observations

“…aeronomie.be/spectrolab/o2.htm) were used. Recently, Wagner et al (2009) and found that the retrieved O 4 SCDs were systematically too high to match the model simulation even under pure Rayleigh conditions, at least at the times and locations of their MAX-DOAS observations. These differences might be induced in the DOAS retrieval by uncertainties in the absolute values of the O 4 cross sections.…”

Observations of the vertical distributions of summertime atmospheric pollutants and the corresponding ozone production in Shanghai, China

“…However, the reason for the uncertainty is not yet well understood. The uncertainty is typically corrected by multiplying the O 4 absorption cross section with a constant correction factor (Wagner et al, 2009Clémer et al, 2010;Chan et al, 2015;Wang et al, 2016). By comparing the measured and modeled O 4 absorptions, we estimated that the literature O 4 absorption cross section was underestimated by 20 %.…”