DOAS Measurements of NO2 at Kinshasa and Comparisons with Satellite Observations
Recent studies show that air pollution also affects Africa. Air quality is worsening in large cities with growing populations. Satellite observations over some Central African cities seem to confirm this pollution for species such as NO2, HCHO and aerosols. The sources of pollution are generally different from those found in Europe for example. In Central Africa, particularly in the Congo Basin, the main sources of NO2 and HCHO emissions are forest fires and the use of embers in cooking. Kinshasa, the capital of the Democratic Republic of Congo, a large megalopolis of about 11 million inhabitants, like several other large cities in Africa, lack ground-based atmospheric measurement systems. To improve this situation, the researchers of the University of Kinshasa (Unikin) in collaboration with the UV-Vis group of the Belgian Institute for Space Aeronomy (IASB) have set up a first installation of a simple atmospheric observation equipment. This equipment was installed on the roof of the Faculty of Sciences of Unikin ( -4.42°S, 15.31°E) in May 2017 and has operated until November 2019. The instrument is based on a compact AVANTES spectrometer covering the spectral range 290 - 450 nm with 0.7 nm resolution. The spectrometer is a Czerny-Turner type with an entry slit of 50 µm wide, and an array of 1200 l/mm. A 10 m long and 600 µm thick diameter optical fiber is connected to the spectrometer to receive the incident light beam from the sky. Measurements were mainly made by looking in a fixed direction. In November 2019, a Multi-Axis DOAS instrument (MAX-DOAS) has been installed to replace the first instrument. The measurements clearly show the signature of polluting species such as NO2 and HCHO in Kinshasa's atmosphere. In this study, we therefore show all the different steps of the algorithm we used to obtain the vertical columns from the observations of the instrument installed in Kinshasa. We present a first comparison of these ground-based observations of NO2 in Kinshasa with those from the OMI and TROPOMI satellites for clear days between May and November 2017.
