Tropospheric boundary layer investigations by differential ground-based solar FTIR spectrometry

In order to better understand the chemistry and the transport mechanisms in the lower troposphere, a new original technique has been developed and tested. The experiment consists in recording high resolution infrared solar absorption spectra containing signatures of important atmospheric constituents, simultaneously from the International Scientific Station of the Jungfraujoch in Switzerland [ISSJ, 3580 m a.s.l., 46.5 degrees N, 8 degrees E, Bruker 120 HR Fourier transform spectrometer (FTS)] and from a nearby valley (Grindelwald, 1070 m a.s.l., Bruker 120 M FTS). Analysis of individual spectra allows to determine vertical column abundances: differences between measurements at ISSJ and at Grindelwald enable us to retrieve the constituents' concentrations between 1070 m and 3580 m, assuming a constant volume mixing ratio in this layer. A first measurement campaign has been organized during the months of May and June 1998. After an initial period of instrument intercomparison at ISSJ, the mobile instrument was moved down in the valley and installed for one month in Grindelwald. When operated side by side at the Jungfraujoch, measurements made by both instruments showed a very good agreement (maximum bias of 1.5%). Analysis of spectra recorded synchronously at the Jungfraujoch and at Grindelwald gave average boundary layer concentrations for a selected set of tropospheric molecules, i.e. methane, nitrous oxide, carbon monoxide and ethane. Comparison with other results and with carbon monoxide in-situ measurements made at ISSJ showed a good agreement.