Showing papers by "Ulrich Platt published in 1996"

Numerical analysis and estimation of the statistical error of differential optical absorption spectroscopy measurements with least-squares methods

Abstract: Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere. Their concentration is retrieved by a numerical analysis of the atmospheric absorption spectra, which often are a combination of overlapping absorption structures of several trace gases. A new analysis procedure was developed, modeling atmospheric spectra with the absorption structures of the individual trace gases, to determine their concentrations. The procedure also corrects differences in the wavelength-pixel mapping of these spectra. A new method to estimate the error of the concentrations considers the uncertainty of this correction and the influence of random residual structures in the absorption spectra.

Long‐term observation of nitrate radicals at the Tor Station, Kap Arkona (Rügen)

Abstract: Long-term observation of the trace gases NO 2 , ozone, and nitrate radicals (NO 3 ) at a rural site in the Baltic Sea (near Kap Arkona, island Rugen) using differential optical absorption spectroscopy (DOAS) are presented here. The time series of these species cover more than 14 months of data. Additionally, meteorological data were taken from the Deutscher Wetterdienst station at Kap Arkona. The average nighttime NO 3 concentration was determined at 7.8 ppt. Maximum lifetimes of more than 5000 s were observed, but average NO 3 lifetimes are close to 250 s. As nitrate radicals are expected to play an important role in the nonphotochemical conversion of NO x to HNO 3 , long-term observations offer a key for investigation of possible sink mechanisms of NO 3 molecules mediated by both homogeneous and heterogeneous reactions. Analysis of the data shows that the NO 3 lifetime is inversely proportional to the NO 2 concentration, thus suggesting that the removal of N 2 O 5 is actually the dominating NO 3 loss process. The mean N 2 O 5 concentration from this long-term measurement was calculated at 1 ppb with an N 2 O 5 lifetime between 1000s and 20000s covering 90 % of the data.

Intercomparison of instruments for tropospheric measurements using differential optical absorption spectroscopy

Abstract: The results of an intercomparison campaign of eight different long path UV-visible DOAS instruments measuring NO2, O3 and SO2 concentrations in a moderately polluted urban site are presented. For effective optical path lengths of 230 and 780 m the overall spread of these measurements (±1σ) are 5×1010, 6×1010 and 1×1010 molec·cm-3 (2.0, 2.4, and 0.4 ppb) for these molecules respectively when all instruments used a common set of absorption cross sections. The remaining differences are not completely random and the systematic differences are attributed to the different retrieval methods used for each instrument.

Measurement of the latitudinal distribution of NO2 column density and layer height in Oct. / Nov. 1993

Abstract: In October/November 1993 DOAS measurements of total columns of NO2 and O3 were performed on a ship cruise from Germany to South Africa. The results are compared to data collected during an earlier campaign with a similar setup [Kreher et al. 1995], which took place in 1990, before the eruption of the Pinatubo volcano. Overall no general trend for NO2 in 1993 in comparison to 1990 could be detected. The O3 vertical column densities in 1993 are mostly around 280 Dobson Units, showing a significant increase to over 330 DU south of 25°S, and significantly lower O3 values south of 50°S. The height of the NO2 concentration maximum was calculated from the NO2 am/pm ratio and data from ozonesondes. The resulting heights are mostly round 29 km, except in the region (south of ≈ 45°S) where the lowest ozone column densities occurred, there the calculated height is ≈ 22 km.