Analysis of 20 years of tropospheric ozone vertical profiles by lidar and ECC at Observatoire de Haute Provence (OHP) at 44° N, 6.7° E

• Published in: Atmospheric Environment
• Main Authors: Gaudel, Audrey, Ancellet, Gérard, Godin-Beekmann, Sophie
• Other Authors: TROPO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), STRATO - LATMOS
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: Transport; Data analysis; Trend; Ozonesonde; Lidar; Ozone; ChArMEx; [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; [SDE]Environmental Sciences; North Atlantic; North Atlantic oscillation
• Online Access: https://insu.hal.science/insu-01144134; https://doi.org/10.1016/j.atmosenv.2015.04.028

International audience ECC (Electrochemical Concentration Cell) ozonesondes and UV DIAL (DIfferential Absorption Lidar) lidar measurements have been carried out simultaneously at OHP (Observatoire de Haute Provence, 44° N, 6.7° E, 690 m) since 1991 and provide: (i) a good basis for long-term trend assessment by two different instruments at the same location and (ii) a 20-year climatology of tropospheric ozone in the Western Mediterranean basin. Air mass trajectories and mixing layer height (MLH) have been calculated for all the ozone observations available at OHP. The bias between the seasonal mean calculated with lidar and ECC ozone vertical profiles for 4 time-periods of 5 years is ∼0.6 ppbv in the free troposphere (4-8 km). Larger differences (≥10 ppbv) are explained by the need for clear sky conditions during lidar observations. Measurements of both instruments have been combined to decrease the impact of short-term atmospheric variability on the trend estimate. In the upper and the mid-troposphere, the spring maximum decreases by 5 ppbv during the 20-year period. In the mid-troposphere, the summer average decreases by 3 ppbv during the 20-year period. At altitude above 4 km, the variability of ozone attributed to different source regions can be in the range of 5-10 ppbv over 20 years and is mitigated by transport variability. In the lower troposphere and after year 2000, there is a sharp 5 ppbv decrease of the spring and summer averages of the surface measurements and of the ECC observations made in the 0.6-4 km altitude range. There is also a decrease of the lowermost troposphere ozone vertical gradient which is explained by the variability of the MLH (mixing layer height). The trends of ozone annual mean show significant decrease of 3 and 4 ppbv/decade from 1998 to 2010 at the surface and at the 2-4 km altitude range, while no significant trends are observed at higher altitude. Positive North Atlantic Oscillation (NAO) periods correspond to positive yearly mean ozone anomalies in the upper troposphere ...