Caroline Fayt

Measurements of Tropospheric NO2 in Romania Using a Zenith-Sky Mobile DOAS System and Comparisons with Satellite Observations

In this paper we present a new method for retrieving tropospheric NO2 Vertical Column Density (VCD) from zenith-sky Differential Optical Absorption Spectroscopy (DOAS) measurements using mobile observations. This method was used during three days in the summer of 2011 in Romania, being to our knowledge the first mobile DOAS measurements peformed in this country. The measurements were carried out over large and different areas using a mobile DOAS system installed in a car. We present here a step-by-step retrieval of tropospheric VCD using complementary observations from ground and space which take into account the stratospheric contribution, which is a step forward compared to other similar studies. The detailed error budget indicates that the typical uncertainty on the retrieved NO2tropospheric VCD is less than 25%. The resulting ground-based data set is compared to satellite measurements from the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment-2 (GOME-2). For instance, on 18 July 2011, in an industrial area located at 47.03°N, 22.45°E, GOME-2 observes a tropospheric VCD value of (3.4 ± 1.9) × 1015 molec./cm2, while average mobile measurements in the same area give a value of (3.4 ± 0.7) × 1015 molec./cm2. On 22 August 2011, around Ploiesti city (44.99°N, 26.1°E), the tropospheric VCD observed by satellites is (3.3 ± 1.9) × 1015 molec./cm2 (GOME-2) and (3.2 ± 3.2) × 1015 molec./cm2 (OMI), while average mobile measurements give (3.8 ± 0.8) × 1015 molec./cm2. Average ground measurements over “clean areas”, on 18 July 2011, give (2.5 ± 0.6) × 1015 molec./cm2 while the satellite observes a value of (1.8 ± 1.3) × 1015 molec./cm2.

Ground-based stratospheric NO2 monitoring at Keflavik (Iceland) during EASOE

This report presents ground based measurements of nitrogen dioxide above Keflavik, Iceland, 64[degrees]N, between December 1991, and February 1992. Using visible spectrometry, the authors observed column densities below 1 [times] 10[sup 15] molecules/cm[sup 2] inside the polar vortex.

Individual Reports from TOPAS Contributors

The work accomplished during the period 1990 to 1995 by the three Belgian groups participating in the EUROTRAC-TOPAS project is described. It involved the construction and permanent improvement of two DOAS (Differential Optical Absorption Spectroscopy) spectrometers. One of these is a Fourier transform instrument which was applied to atmospheric measurements in the Visible-UV region for the first time. Long path absorption set-ups were constructed. Software was developped to operate and automate the instruments and specific algorithms were written for the retrieval of concentrations from the atmospheric spectra. Both instruments were validated by participating in two EUROTRAC-TOPAS intercomparison campaigns which gathered instruments from six european countries. Finaly, high resolution absorption cross sections of several atmospherically relevant species were measured in the laboratory.