Skip to Content

How the MAX-DOAS technique can help to fill the gap between in situ and satellite observations

Satellite measurements of tropospheric constituents have advanced significantly over the last decade, now providing near global measurements of a number of species relevant in tropospheric chemistry (e.g. CO, NO2, HCHO, SO2, CHO.CHO). With improving spatial resolution, these data sets move towards air pollution monitoring and even air quality assessment. However, the integrating nature of this type of remote sensing measurements makes the link to in-situ data as they are usually provided by monitoring networks difficult. This is a problem for both validation and interpretation of the satellite data. Multi-axis differential absorption spectroscopy (MAX-DOAS) measurements can improve on this situation in several ways. Firstly, they can be used to provide directly the integrated tropospheric columns which are the quantity needed for validation. Secondly, they offer some vertical resolution, information which is needed in the retrieval of satellite data. Furthermore, their relatively high temporal resolution enables MAX-DOAS to sample the diurnal cycle of trace gases which is not covered by satellite instruments, yielding insight in the photochemistry of atmospheric pollutants.

This talk gives an overview on studies using observations from the “Bremian DOAS measurement network” BREDOM. It comprises in total six different stations from high (79°N) to low latitudes (1°S). One very recent work which is presented in more detail is the usage of MAX-DOAS instruments to establish a monitoring system for main shipping routes. MAX-DOAS observations of NO2 and SO2 are carried out from two permanent sites close to the Elbe river (Wedel, Germany) and on the island Neuwerk close to the mouths of Elbe and Weser since the year 2013. Mixing ratios of both trace gases have been retrieved using different approaches (pure geometric and taking into account the radiative transfer) and compared to in situ observations. Furthermore, emission factors of NO 𝑥 and SO2 have been calculated for single ships.