Earthshine and solar irradiance spectra 300..800 nm

Fig 3.3.1.2.1: Earthshine and solar irradiance spectra 300..800 nm with inset 425..450 nm range.

Image: AT2-ELS

Fig 3.3.1.2.2: Earthshine and solar irradiance spectra 425..450 nm

Image: AT2-ELS

For the purposes of this step-by-step presentation we shall focus on the measured earthshine and solar irradiance spectra between 425 and 450 nm. We have chosen this wavelength range because:

The reference spectrum for a species can contain certain ranges where absorption changes particularly rapidly with changing wavelength.
The DOAS technique focuses on the regions of rapidly changing absorption levels.
In the case of the spectrum of our target substance NO₂, the range 425..450 nm shows a large number of rapid changes in absorption.
In this spectral region there is little interference by other absorbing species.