Inversion of tropospheric profiles of aerosol extinction and HCHO and NO<sub>2</sub> mixing ratios from MAX-DOAS observations in Milano during the summer of 2003 and comparison with independent data sets

Abstract

Abstract. We present aerosol and trace gas profiles derived from MAX-DOAS observations. Our inversion scheme is based on simple profile parameterisations used as input for an atmospheric radiative transfer model (forward model). From a least squares fit of the forward model to the MAX-DOAS measurements, two profile parameters are retrieved including integrated quantities (aerosol optical depth or trace gas vertical column density), and parameters describing the height and shape of the respective profiles. From these results, the aerosol extinction and trace gas mixing ratios can also be calculated. We apply the profile inversion to MAX-DOAS observations during a measurement campaign in Milano, Italy, September 2003, which allowed simultaneous observations from three telescopes (directed to north, west, south). Profile inversions for aerosols and trace gases were possible on 23 days. Especially in the middle of the campaign (17–20 September 2003), enhanced values of aerosol optical depth and NO2 and HCHO mixing ratios were found. The retrieved layer heights were typically similar for HCHO and aerosols. For NO2, lower layer heights were found, which increased during the day. The MAX-DOAS inversion results are compared to independent measurements: (1) aerosol optical depth measured at an AERONET station at Ispra; (2) near-surface NO2 and HCHO (formaldehyde) mixing ratios measured by long path DOAS and Hantzsch instruments at Bresso; (3) vertical profiles of HCHO and aerosols measured by an ultra light aircraft. Depending on the viewing direction, the aerosol optical depths from MAX-DOAS are either smaller or larger than those from AERONET observations. Similar comparison results are found for the MAX-DOAS NO2 mixing ratios versus long path DOAS measurements. In contrast, the MAX-DOAS HCHO mixing ratios are generally higher than those from long path DOAS or Hantzsch instruments. The comparison of the HCHO and aerosol profiles from the aircraft showed reasonable agreement with the respective MAX-DOAS layer heights. From the comparison of the results for the different telescopes, it was possible to investigate the internal consistency of the MAX-DOAS observations. As part of our study, a cloud classification algorithm was developed (based on the MAX-DOAS zenith viewing directions), and the effects of clouds on the profile inversion were investigated. Different effects of clouds on aerosols and trace gas retrievals were found: while the aerosol optical depth is systematically underestimated and the HCHO mixing ratio is systematically overestimated under cloudy conditions, the NO2 mixing ratios are only slightly affected. These findings are in basic agreement with radiative transfer simulations.

Validation of OMI, GOME-2A and GOME-2B tropospheric NO<sub>2</sub>, SO<sub>2</sub> and HCHO products using MAX-DOAS observations from 2011 to 2014 in Wuxi, China: investigation of the effects of priori profiles and aerosols on the satellite products

“…Thus the SFs at high altitudes could be underestimated by MAX-DOAS retrievals. This effect could be considerable, especially for SO 2 and HCHO, because they typically extend to higher altitudes than NO 2 (Xue et al, 2010;Junkermann, 2009;Wagner et al, 2011). Because BAMFs of satellite observations are normally larger at high altitudes, the uncertainties of SFs from MAX-DOAS could cause an underestimation of AMF MAX−DOAS , which further could cause an overestimation of VCD SM .…”

“…Frieß et al, 2006Frieß et al, , 2011Frieß et al, , 2016Wittrock et al, 2006b;Irie et al, 2008Irie et al, , 2011Clémer et al, 2010;Li et al, 2010, X. Li et al, 2013Vlemmix et al, 2010Vlemmix et al, , 2011Vlemmix et al, , 2015bWagner et al, 2011;Yilmaz, 2012;Hartl and Wenig, 2013;Wang et al, 2013a, b). MAX-DOAS observations provide valuable information that can be applied for a quantification of air pollutants (e.g.…”

Evaluation of tropospheric SO<sub>2</sub> retrieved from MAX-DOAS measurements in Xianghe, China

“…It is based on the measurement of sunlight scattered at multiple elevation angles towards the horizon, thus increasing the sensitivity to absorbers present close to the ground compared to the zenith viewing geometry (Hönninger et al, 2004). MAX-DOAS studies published so far have been mainly focused on the retrieval of NO 2 (e.g., Wittrock et al, 2004;Vlemmix et al, 2010;Frins et al, 2012;Hendrick et al, 2014;Ma et al, 2013;Wang et al, 2014), halogen oxides like BrO and IO (e.g., Frieß et al, 2011;Großmann et al, 2013), formaldehyde (e.g., Heckel et al, 2005;Wagner et al, 2011), and aerosols (e.g., Wagner et al, 2004;Frieß et al, 2006;Clémer et al, 2010). A lot of work has been done on MAX-DOAS measurements of volcanic SO 2 (e.g., Bobrowski et al, 2007;Galle et al, 2010), but so far only a few studies deal with MAX-DOAS observations of this species in polluted areas (e.g., Irie et al, 2011;Lee et al, 2008;Wu et al, 2013), despite the fact that, as for other trace gases like NO 2 , HCHO, and BrO, the combination of both surface concentration and VCD retrievals makes MAX-DOAS a useful technique for validating SO 2 satellite data.…”

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.…”