Measurements of atmospheric composition in madrid using the doas technique

Resumen

This thesis is focused on measurements of trace gases in the atmosphere of Madrid (Spain) and their assessment and relationship with urban pollution and air quality. The remote-sensing, ground-based Multi AXis Differential Optical Absorption Spectroscopy (MAXDOAS) technique has been used. A complete analysis of NO2, HONO, glyoxal and formaldehyde vertical concentration profiles in the urban atmosphere of Madrid has been performed. Our MAXDOAS-1D instrument (located within the city centre) was operating during the entire year of 2016 allowing the retrieval of diurnal and seasonal cycles of these trace gases. Using DOAS spectral fitting methods and a radiative transfer model, information on vertical columns and their altitude-distributed concentrations were retrieved. The RTM simulates the atmosphere, resulting in vertical profiles of the aerosols extinction coefficients, nitrogen dioxide, nitrous acid, glyoxal and formaldehyde concentrations. A new MAXDOAS-2D instrument was built from scratch and a complete analysis of O4 and NO2 vertical concentration profiles in the urban atmosphere of Madrid (Spain) has been performed over two months (from May 6 to July 5, 2019). It provides a two-dimensional view (in height and Viewing Azimuth Angle) of irradiance extinction and NO2 concentration profiles. Moreover, we also carried out the HONO analysis, providing vertical, two-dimensional profiles of this trace gas as well. We inferred data on the horizontal gradient of NO2 within the surface layer making use of the different light paths travelled by photons at different spectral regions. The “onion-peeling” method yielded peak values of NO2 in the early morning and in the southern section of the city (around 180 ° VAA). We suggest that the new mesoscale information provided by the MAXDOAS-2D instrument may help in the study of pollution transport dynamics in Madrid. In addition, it is shown that this technique complements very well the in situ monitoring of trace gases, providing information at a larger spatial scale for the overall analysis of air pollution in Madrid.