QualAir atmospheric measurement at University Pierre et Marie Curie, Paris
Résumé
QualAir is a joint remote-sensing observation platform from LATMOS and LPMAA, located in Paris city centre. It addresses the need for information about pollutant vertical distributions to improve our understanding of pollution peak processes and assess ground-based air quality measurements representativity. Moreover, it offers possibilities for satellite validation over urban areas.
The station measures integrated columns of NO2 (SAOZ UV-visible zenith-sky
spectrometer), atmospheric pollutants (infrared Fourier transform spectrometer) and aerosols (AERONET sun photometer). An elastic backscatter lidar provides aerosol extinction profiles and observations of boundary layer (BL) height variability.
Here, BL depth is determined from lidar data on an hourly basis. BL top is defined as the altitude of minimal signal gradient or as the cloud base, if a cloud is capping the BL. The same treatment is applied to SIRTA lidar data to show regional variability of BL depth. Results are presented in Figure 2 for both MEGAPOLI campaigns, together with ECMWF forecasts. In summer during daytime, the effect of solar radiation and convection is predominant and there is no noticable difference between Paris centre and suburbs. In winter, as the solar flux is lower, BL depth over the city tends to be higher due to the heat island effect. ECMWF forecasts agree reasonably well to observations given their low temporal resolution.
The very high resolution Fourier transform spectrometer of the LPMAA records the infrared solar spectra from QualAir roof. The spectral region (3.1-5.1μm) is selected to monitor atmospheric pollutants like CO, CO2, N2O, O3, H2O, CH4, HCl, HF. The spectral signature of those gases allows to retrieve their abundances in the atmosphere using a radiative transfer algorithm. Figure 3 shows the P(8) CO absorption line (located at 2111.543 cm-1) that is used to determine the CO concentration vertical profile for July 1st 2009 (Figure 4). Fluctuating signals around 35500 s are due to the thin clouds presence. The CO volume mixing ratio obtained by the FTIR at ground level (on average, 0.31 ± 0.05 ppmv) compared well to the CO in-situ measurements from QualAir CO11M analyzer (on average, 0.27 ± 0.10 ppmv).