Remote sensing of exceptional winter aerosol pollution events and representativeness of the surface – column relationship over Paris metropolitan area
Journal Article
Abstract. In this study an optical parameter derived from lidar measurements is found to be relevant to monitor the evolution of near-surface particulate concentrations. This highlights the opportunities offered by future spaceborne lidar missions in air quality assessment on a global scale. This work is carried out following a dedicated field campaign in the Paris area (France) during winter 2016–2017, from 1st November to 31st January. Two of the most intense winter aerosol pollution events occurring over the last decade were sampled using a ground-based N2-Raman. The lidar operated continuously at the wavelength of 355 nm, favourable to the measurement of submicron aerosols mainly linked to traffic emissions. The data analysis uses the synergy between ground-based and spaceborne lidar observations, and data from the air quality monitoring network Airparif. The first severe aerosol pollution event occurred on 1st December 2016; it concerned a circular area of 250 km in diameter around Paris with maximum PM10 (PMx is the mass concentration of particles with an aerodynamic diameter smaller than x µm) values of 121 ± 63 µg m-3. The second event took place from 21st to 22nd January which covered all of Western Europe, with maxima of PM10 (156 ± 33 µg m-3) and aerosol extinction coefficient (AEC) between 0.6 and 1 km-1, within the winter atmospheric boundary layer. These two major aerosol pollution events share very low boundary layer height, down to 300 m above ground level. However, they did not take place in the same weather condition; moreover, they are associated with significantly different lidar ratios: 72 ± 15 sr and 56 ± 15 sr, respectively in December and January. Such results are consistent with available spaceborne lidar data (70 ± 25 sr) and values found in the literature. During these two events, the continuous temporal evolution of the aerosol extinction coefficient allows us to investigate the representativeness of optical parameters found in the planetary boundary layer to assess surface aerosol concentration. No one-to-one relationship between the aerosol optical thickness (AOT) and PM2.5 values stands out within our study. In contrast, the maximum lidar-derived aerosol extinction coefficient found within the planetary boundary layer is identified as a consistent variable to assess the evolution of ground aerosol concentration.;
