MAX‐DOAS O₄ measurements: A new technique to derive information on atmospheric aerosols—Principles and information content

Abstract

[1] Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of the oxygen dimer O 4 which can serve as a new method for the determination of atmospheric aerosol properties are presented. Like established methods, e.g., Sun radiometer and LIDAR measurements, MAX-DOAS O 4 observations determine optical properties of aerosol under atmospheric conditions (not dried). However, the novel technique has two major advantages: It utilizes differential O 4 absorption structures and thus does not require absolute radiometric calibration. In addition, O 4 observations using this method provide a new kind of information: since the atmospheric O 4 profile depends strongly on altitude, they can yield information on the atmospheric light path distribution and in particular on the atmospheric aerosol profile. From O 4 observations during clear days and from atmospheric radiative transfer modeling, we conclude that our new method is especially sensitive to the aerosol extinction close to the ground. In addition, O 4 observations using this method yield information on the penetration depth of the incident direct solar radiation. O 4 observations at different azimuth angles can also provide information on the aerosol scattering phase function. We found that MAX-DOAS O 4 observations are a very sensitive method: even aerosol extinction below 0.001 could be detected. In addition to the O 4 absorptions we also investigated the magnitude of the Ring effect and the (relative) intensity. Both quantities yield valuable further information on atmospheric aerosols. From the simultaneous analysis of the observed O 4 absorption and the measured intensity, in particular, information on the absorbing properties of the aerosols might be derived. The aerosol information derived from MAX-DOAS observations can be used for the quantitative analysis of various trace gases also analyzed from the measured spectra.

The Heidelberg Airborne Imaging DOAS Instrument (HAIDI) – a novel imaging DOAS device for 2-D and 3-D imaging of trace gases and aerosols

“…Tech., 7, 3459-3485, 2014 www Baidar et al, 2013;Dix et al, 2013). This is usually done in a two-stage process using inverse modeling of the atmospheric radiative transfer (e.g., Sinreich et al, 2005;Wagner et al, 2004;Frieß et al, 2006;Irie et al, 2008;Clémer et al, 2010;Wagner et al, 2011). First, the aerosol extinction profile is retrieved from the absorption of the oxygen collision complex O 4 , which has a horizontally constant atmospheric concentration (apart from pressure variations) and therefore serves as a proxy of the light path which is affected by aerosols.…”

NO<sub>2</sub> observations over the western Pacific and Indian Ocean by MAX-DOAS on <i>Kaiyo</i>, a Japanese research vessel

“…Hönninger et al, 2004;Wagner et al, 2004;Wittrock et al, 2004;Sinreich et al, 2005;Frieß et al, 2006). It is useful for measuring a priori profiles for satellite retrievals and for validating chemical transport models.…”

Reactive bromine in the low troposphere of Antarctica. Estimations at two research sites

“…Either with active set-ups (e.g., Long path-DOAS) or with passive 10 ones (e.g., zenith-DOAS, MAX-DOAS, satellite observations), the DOAS technique has been used broadly to research the troposphere in remote environments (e.g., Wagner and Platt, 1998;Bobrowsky et al 2003;Wagner et al, 2007;Saiz-Lopez et al, 2007a,b;Puentedura, et al 2012, Prados-Roman et al, 2015Peterson et al, 2017). In particular, the MAX-DOAS instrumental set-up referred to in this work consists in a telescope scanning the atmosphere at different elevation angles inferring with it vertically-resolved information of the status of the atmosphere regarding aerosols and trace gases (e.g., 15 Hönninger et al, 2004;Wagner et al, 2004). This is indeed an advantage that the MAX-DOAS configuration offers over the standard set-up of the e.g.…”

“…This retrieval is based on the concept that the concentration O4 is known and stable in the atmosphere. Hence, a variation 5 in the O4 dSCDs is usually related to a change of the optical path, generally due to the presence of aerosols (e.g., Hönninger et al, 2004;Wagner et al, 2004). The inverted AEC vertical profile was then used as input for the linear inversion of the vertical profile of BrO vmr.…”