Measurement of atmospheric nitrogen dioxide column density by solar spectroscopic method

Nitrogen Dioxide (NO₂) column density was studied by solar spectroscopic method. In the retrieval of NO₂ column density, the Kitt Peak Solar Flux Atlas provides a standard reference of the extraterrestrial solar spectrum. However, in order to eliminate the Fraunhofer features from the solar spectrum, the ground-level solar spectrum needs to be re-scaled for wavelength correction and resolution matching to the reference Kitt Peak Solar spectrum. The analysis procedure becomes much simplified if both the reference and the ground-level solar spectra are captured by the same instrument. A portable miniature charge-coupled device (CCD) spectrometer was employed to acquire both the reference and ground-level solar spectra. The reference spectrum was captured in Xinjiang (42.107°N, 83.750°E), the People's Republic of China, during a flight in a plane. The altitude of the reference solar spectrum is 11,230 meters above the sea level. The ground-level solar spectrum was acquired in the campus of City University of Hong Kong (22.336°N, 114.173°E) using a computer-controlled solar tracker. By analyzing the solar spectra obtained at two different locations and altitudes, NO₂ total column density can be deduced.