Long-term MAX-DOAS measurement of trace gases and aerosol in the Environmental Research Station Schneefernerhaus

The Environmental Research Station Schneefernerhaus (Umwelt Forschungsstation Schneefernerhaus, UFS) is located immediately under the summit of Zugspitze (2962 m), the highest mountain of Germany, at a height of 2650 m. The UFS is a rare observation site in Germany with mostly clean and unpolluted air. It is ideal for both stratospheric composition measurements and trace gas measurements in the free-troposphere. It is optimal for detecting pollution events in the free-troposphere, which are indications of short- or long-range transport of air pollutants. Long-term atmospheric measurements in the UFS can provide valuable information for the study of atmospheric environment. A MAX-DOAS instrument has been working in the UFS since February 2011. There are two temperature stabilized spectrometers, one for UV (320-478 nm) region, and the other for VIS (427-649 nm) region. The spectra measured by the two spectrometers are recorded synchronously. The differential slant column densities (DSCDs) of trace gases are calculated from the spectra with Differential Optical Absorption Spectroscopy (DOAS) method. The zenith spectrum of each cycle is used as the reference. The DSCDs of O4 are calculated in two different wavelength intervals, 338-370 nm in the UV region and 440-490 nm in the VIS region. The DSCDs of NO2 are calculated in the same wavelength intervals as O4. For HCHO and HONO, optimal fitting windows have been determined in the UV region. A retrieval algorithm, based on the radiative transfer model LIDORT and the optimal estimation technique, is used to provide information on the vertical profiles and vertical column densities (VCDs) of aerosol and trace gases. Meantime, zenith-sky radiance spectra at large solar zenith angle (SZA) are analyzed using DOAS method to derive total ozone columns and stratospheric NO2 columns. A zenith spectrum measured in the noon of a summer day was chosen as the reference spectrum. Ozone and NO2 SCDs, which are the direct product of the DOAS analysis, are then converted into VCDs using the air mass factors (AMFs) derived by radiative transfer calculations. This work presents the result of the MAX-DOAS measurement in the UFS from 2012 to 2015, including aerosol (derived from O4 measurement), NO2, HCHO, and HONO, etc. The vertical profiles as well as the seasonal and diurnal variation patterns of tropospheric aerosol and trace gases will be shown. The total O3 and stratospheric NO2 columns, as well as a comparison between zenith-sky measurement and satellite measurement will also be shown.