Latmos UPMC/CNRS - ILRC 2015 long term tropospheric ozone trends measured by lidar and ECC ozonesondes from 1991 to 2015 in Southern France G. Ancellet, A. Gaudel, S. Godin-Beekmann ECC LIDAR OHP NDACC Station 44N, 6E 700 m asl Surface ozone monitor Latmos UPMC/CNRS - ILRC 2015

OHP tropospheric ozone lidar Transmitter: Nd:YAG + SRS in D2 20 Hz, 10 mJ at 289 and 316 nm (266 nm not used) Receiver: 80 cm telescope diameter Grating spectrometer LICEL data acquisition system (analog + photocounting) Measurement altitude: 4-15 km asl (1991-1993) 3-15 km asl (1993-2011) 2.5-15 km asl (2012-today) Integration time ≈ 1 hour (sunset) 2 profiles per week on average O3 concentration accuracy (intercomparison campaigns with balloon and aircraft) ≤ 7 % Data removed in cloud or thick aerosol layers Overlap function correction in the 2-4 km range. Major changes: - March 1993: switch from 2 Raman cells (289/299 nm) to one (289/316 nm) - March 2012: switch to LICEL data acquisition, more stable optical design between laser and telescope Latmos UPMC/CNRS – LWG 2016

Ozone profile vertical/temporal averaging for the study of the interannual variability Lidar ECC NAO Pinatubo 2003 1991 1995 1996 2000 2001 2005 2006 2010 2011 2015 611 profiles 593 profiles 445 profiles 504 profiles 539 profiles Lidar 390 profiles 337 profiles 232 profiles 260 profiles 290profiles ECC 221 profiles 256 profiles 213profiles 244 profiles 249 profiles Surface O3 Latmos UPMC/CNRS -LWG 2016

Air mass transport assessment and PTU vertical profiles at OHP ERA interim ECMWF analysis 1° resolution 60 vertical levels: Temperature, humidity, PV vertical profiles from 0 to 20 km for each lidar and ECC profiles Flextra 4 days backward trajectories: 700 hPa, 500 hPa, 400 hPa, Tropopause Layer (2km below PV=1.5) Arctic Europe America Asia

Comparison of 5-year O3 seasonal averages Less southerly flow for lidar than for ECC in 2005-2013 Period 1991-1995 small transport differences Good proxy for ECC –lidar bias ≤-1 ppb Latmos UPMC/CNRS – LWG 2016

Trend above 6km are significant Trends - Global According to IPCC method trends are defined as Virtually certain: pvalue < 0.01 Very likely: pvalue < 0.1 Likely: pvalue < 0.34 About as likely as not: pvalue = 0.67-0.34 Unlikely: pvalue > 0.67 Very unlikely: pvalue > 0.90 Exceptionally unlikely: pvalue > 0.99 Trend above 6km are significant Decrease only at the surface for which there is ECC data only

Trends per region Number of data is reported on the figure for each year For Europe: - Trends are quite similar to the global trends For America: - Likely trend at 2-4km and higher than global - Not likely trends at 4-6km and close to the surface and trends values are lower than global

Trends per region Number of data is reported on the figure for each year Fore Arctic and Asia, very low sampling, not sure we can use it…

Trends per PV range Number of data is reported on the figure for each year For PV < 0.75 Pvu or PV > 0.75PVu trends quite similar to the global trends, Except for UT for which trend’s value is lower than for global (0.24ppbv/yr instead of 0.37ppbv/yr)

Conclusions 24-year regular tropospheric O3 measurements with two different instruments (ECC and lidar) Meteorological bias for lidar measurements and instrumental bias between ECC and lidar less than -1 ppbv for 5-year seasonal averages in the free troposphere (consistent with lidar accuracy during intercomparison campaign < 7%) Need to use both ECC and lidar measurements to improve the interannual variability analysis No O3 trend in the mid troposphere while there is a significant positive trend (3 ppbv/decade) below the tropopause At 700 hPa variable trend probably linked to NAO and large transport Decrease in the PBL (-1.4 ppbv/decade) consistent with ground-based ozone trend in Southern Europe Latmos UPMC/CNRS - LWG 2016

Latmos UPMC/CNRS - ILRC 2015 Perspectives Projet Tropospheric Ozone Assessment Report (TOAR) dans cadre IGAC: rendu en 2017 Réseau lidar troposphérique TOLNET aux USA associant NASA, NOAA, NCAR (coordination M. Newchurch, Huntsville) Activité de Ozone sonde expert group pour harmonization longues series de mesure: mise à jour des 1171 sondes OHP avec tous les paramètres permettant ce travail (merci à Nathalie Poulet !) Latmos UPMC/CNRS - ILRC 2015