Analysis of ozone vertical profile day-to-day variability in the lower troposphere during the Paris-2022 ACROSS campaign

Abstract. The ozone vertical profiles variability in the lower troposphere is analyzed during the summer 2022 ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) measurement campaign as part of the PANAME (PAris region urbaN Atmospheric observations and models for Multidisciplinary rEsearch) project. The analysis is based on 21 days of DIfferential Absorption Lidar (DIAL) observations, in addition to the two daily vertical ozone profiles measured by In-service Aircraft for a Global Observing System (IAGOS) flights to and from Paris airport. The ACROSS ozone profiles are also a good opportunity to assess the lowermost tropospheric ozone column retrieval by the satellite observations of Infrared Atmospheric Sounding Interferometer (IASI). The planetary boundary layer (PBL) vertical structure evolution is monitored using a 808-nm microlidar and meteorological radiosondes launched in the city center. Characterization of the regional transport of polluted air masses advected over the city is based on the daily ozone analysis of the Copernicus Atmospheric Service (CAMS) ensemble model and on backward trajectories of the Paris city plume. This work show that the CAMS simulations of the Paris ozone plume between the surface and 3 km are consistent with the ACROSS ozone vertical profiles and that the IASI satellite observations can capture the day to day variability of the 0–3 km lowermost ozone column if the contribution of the surface column below 1.2 km is lower than 4 DU. The day time ozone vertical structure above the city center is also in good agreement with the PBL growth during the day and with the formation of the residual layer during the night. The O₃ DIAL may provide additional information about the PBL vertical structure to discuss differences between microlidar and radiosounding measurements of the PBL height.

In addition to the well-known control of the ozone photochemical production by atmospheric temperature, cloud cover and mixing between the surface layer (0–500 m) and the residual layer, the comparison of four ozone pollution events shows that the thickness of the PBL during the day and the advection of regional scale plumes above the PBL can significantly change the ozone concentrations above Paris city center. With similar cloud cover and air temperature, high ozone concentrations up to 180 µg.m^-3 are encountered during the day when PBL height is below 1.5 km, while they remain below 150 µg.m^-3 when PBL height increases above 2.5 km. Advection of ozone poor concentrations in the free troposphere during a Saharan dust event is able to mitigate the ozone photochemical production. On the other hand, the advection of a continental pollution plume with high ozone concentrations > 140 µg.m^-3 maintained high concentrations in the surface layer despite a temperature decrease and cloud cover development.