1ARPA Valle d'Aosta, Saint-Christophe, Italy
2Department of Physics, Sapienza – University of Rome, Rome, Italy
3Izaña Atmospheric Research Center, AEMET, Tenerife, Canary Islands, Spain
4Full Spectrum Science Inc., Toronto, Ontario, Canada
5Department of Earth & Space Science and Engineering, York University, Toronto, Ontario, Canada
6Área de Investigación e Instrumentación Atmosférica, INTA, Torrejón de Ardoz, Spain
7Institute for Meteorology and Climate Research, IMK-ASF, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
Received: 27 May 2014 – Discussion started: 21 Jul 2014
Abstract. A new algorithm to retrieve nitrogen dioxide (NO2) column densities using MKIV ("Mark IV") Brewer spectrophotometers is described. The method includes several improvements, such as a more recent spectroscopic data set, the reduction of measurement noise, interference by other atmospheric species and instrumental settings, and a better determination of the zenith sky air mass factor. The technique was tested during an ad hoc calibration campaign at the high-altitude site of Izaña (Tenerife, Spain) and the results of the direct sun and zenith sky geometries were compared to those obtained by two reference instruments from the Network for the Detection of Atmospheric Composition Change (NDACC): a Fourier Transform Infrared Radiometer (FTIR) and an advanced visible spectrograph (RASAS-II) based on the differential optical absorption spectrometry (DOAS) technique. To determine the extraterrestrial constant, an easily implementable extension of the standard Langley technique for very clean sites without tropospheric NO2 was developed which takes into account the daytime linear drift of stratospheric nitrogen dioxide due to photochemistry. The measurement uncertainty was thoroughly determined by using a Monte Carlo technique. Poisson noise and wavelength misalignments were found to be the most influential contributors to the overall uncertainty, and possible solutions are proposed for future improvements. The new algorithm is backward-compatible, thus allowing for the reprocessing of historical data sets.
Revised: 08 Oct 2014 – Accepted: 22 Oct 2014 – Published: 28 Nov 2014
Diémoz, H., Siani, A. M., Redondas, A., Savastiouk, V., McElroy, C. T., Navarro-Comas, M., and Hase, F.: Improved retrieval of nitrogen dioxide (NO2) column densities by means of MKIV Brewer spectrophotometers, Atmos. Meas. Tech., 7, 4009-4022, doi:10.5194/amt-7-4009-2014, 2014.