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NO2 VCDs from zenith-sky DOAS

The MAX-DOAS instrumet at Cabauw.
Figure 1: Set-up of the BIRA-IASB MAX-DOAS instrument during the CINDI campaign at Cabauw, The Netherlands.
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Recently a new algorithm for retrieving tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) from ground-based zenith-sky (ZS) measurements of scattered sunlight was published in AMTD. The method is based on a four-step approach consisting of (1) the Differential Optical Absorption Spectroscopy (DOAS) analysis of ZS radiance spectra using a fixed reference spectrum corresponding to low NO2 absorption, (2) the determination of the residual amount in the reference spectrum using a Langley-plot-type method, (3) the removal of the stratospheric content from the daytime total measured slant column based on stratospheric VCDs measured at sunrise and sunset, and simulation of the rapid NO2 diurnal variation, (4) the retrieval of tropospheric VCDs by dividing the resulting tropospheric slant columns by appropriate air mass factors (AMFs). These steps are fully characterized and recommendations are given for each of them. The retrieval algorithm is applied on a ZS dataset acquired with a Multi-AXis (MAX-) DOAS instrument during the Cabauw (51.97° N, 4.93° E, sea level) Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI) held from the 10th of June to the 21th of July, 2009 in the Netherlands. The tropospheric VCD amounts derived from ZS observations are compared to VCDs retrieved from off-axis and direct-sun measurements of the same MAX-DOAS instrument as well as to data from a co-located Système d’Analyse par Observations Zénithales (SAOZ) spectrometer. The retrieved tropospheric VCDs are in good agreement with the different datasets with correlation coefficients and slopes close to or larger than 0.9. The potential of the presented ZS retrieval algorithm is further demonstrated by its successful application on a 2-year dataset, acquired at the NDACC (Network for the Detection of Atmospheric Composition Change) station Observatoire de Haute Provence (OHP; Southern France).

Tropospheric NO2
Figure 2: : Tropospheric vertical column density monthly mean time series at the OHP station for zenith-sky DOAS, SAOZ and MAX-DOAS for the period August 2012 – July 2014. The error bars on the MAX-DOAS data points correspond to the one-sigma standard deviation.

Online article:

Please cite this article as: Tack, F., Hendrick, F., Goutail, F., Fayt, C., Merlaud, A., Pinardi, G., Hermans, C., Pommereau, J.-P., and Van Roozendael, M.: Tropospheric nitrogen dioxide column retrieval from ground-based zenith-sky DOAS observations, Atmos. Meas. Tech. Discuss., 8, 935-985, doi:10.5194/amtd-8-935-2015, 2015.


F. Tack (
Last update on 24 Apr 2015