Abstract
Abstract. A first direct intercomparison of aerosol vertical profiles from Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations, performed during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) in summer 2009, is presented. Five out of 14 participants of the CINDI campaign reported aerosol extinction profiles and aerosol optical thickness (AOT) as deduced from observations of differential slant column densities of the oxygen collision complex (O4) at different elevation angles. Aerosol extinction vertical profiles and AOT are compared to backscatter profiles from a ceilometer instrument and to sun photometer measurements, respectively. Furthermore, the near-surface aerosol extinction coefficient is compared to in situ measurements of a humidity-controlled nephelometer and dry aerosol absorption measurements. The participants of this intercomparison exercise use different approaches for the retrieval of aerosol information, including the retrieval of the full vertical profile using optimal estimation and a parametrised approach with a prescribed profile shape. Despite these large conceptual differences, and also differences in the wavelength of the observed O4 absorption band, good agreement in terms of the vertical structure of aerosols within the boundary layer is achieved between the aerosol extinction profiles retrieved by the different groups and the backscatter profiles observed by the ceilometer instrument. AOTs from MAX-DOAS and sun photometer show a good correlation (R>0.8), but all participants systematically underestimate the AOT. Substantial differences between the near-surface aerosol extinction from MAX-DOAS and from the humidified nephelometer remain largely unresolved.
Highlights
Aerosols play an important role in the atmospheric system
We have presented a first direct intercomparison of aerosol extinction profiles, aerosol optical thickness (AOT), and surface extinction from MultiAxis Differential Optical Absorption Spectroscopy (MAXDOAS) measurements
MAX-DOAS data collected during the Campaign of Nitrogen Dioxide measuring Instruments (CINDI) campaign have been compared to independent measurements of the AOT from an AERONET sun photometer, of the vertical structure from a commercial ceilometer instrument, and of the surface extinction from in situ instruments
Summary
Aerosols play an important role in the atmospheric system. Aerosol particles scatter and absorb radiation and affect the formation, optical properties, and lifetime of clouds and have an impact on the radiation balance of the Earth’s atmosphere. The usage of MAX-DOAS measurements for the retrieval of atmospheric aerosol properties (Hönninger et al, 2004; Wagner et al, 2004; Frieß et al, 2006) has found a growing number of applications during recent years (e.g., Irie et al, 2008, 2009; Lee et al, 2009; Takashima et al, 2009; Clémer et al, 2010; Li et al, 2010; Vlemmix et al, 2010; Zieger et al, 2011; Frieß et al, 2011; Wagner et al, 2011; Sinreich et al, 2013; Wang et al, 2014; Hendrick et al, 2014; Vlemmix et al, 2015) As part of these studies, MAX-DOAS aerosol profiles, aerosol optical thickness (AOT), and/or surface extinction were compared to established instrumentation, such as lidar, sun photometer, and in situ aerosol instruments. Measured O4 dSCDs allows us to investigate differences in the various retrieval algorithms, which use a variety of different approaches, as well as the choice of different retrieval parameters (e.g., the a priori)
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