TOAR-II HEGIFTOM Focus Working Group

Tropospheric ozone column amounts in both DU and ppbv (column averaged ozone concentrations, i.e. XO3) are provided at the HEGIFTOM ftp-server, connection details are found here. Those TrOCs are provided for all measurements (L1), together with daily means (L2) and monthly means (L3).

These are the different tropospheric ozone metrics used:

• entire tropospheric ozone column, with upper limit the thermal tropopause height/pressure, both in DU and ppbv [DU_TP and XO3_TP]
• tropospheric ozone column with upper limit a varying pressure level, as a function of latitude: p = 150 hPa for tropics (i.e. |ϕ| < 15°), 200 hPa (15° < |ϕ| < 30°),  300 hPa  (30° < |ϕ| < 60°), 400 hPa ( (|ϕ| > 60°) [DU_plat and XO3_plat]
• tropospheric ozone column with p > 300 hPa [DU_p300 and XO3_p300]
• free-tropospheric ozone column with 300 hPa < p < 700 hPa [DU_FTp and XO3_FTp]
• free-tropospheric ozone column with 4 km < h < 8 km  [DU_FTh and XO3_FTh]
• lower-tropospheric ozone column with p > 700 hPa [DU_LTp and XO3_LTp]
• lower-tropospheric ozone column with h < 4 km [DU_LTh and XO3_LTh]
• boundary layer ozone column with h < 2 km [DU_BL and XO3_BL]

Not every technique (except ozonesondes) is able to provide all those TrOCs. More information is available in the different README files for each technique: O3S_TrOCs_README.xlsx, FTIR_TrOCs_README.xlsx, Lidar_TrOCs_README_v1.xlsx, IAGOS_TrOCs_README.txt, and Umk_README_NOAA_01302024.txt.

Next to the TrOCs, we also provide for each TrOC metric, if possible, the random uncertainty (RUnc_*), systematic uncertainty (SUnc_*), total uncertainty (Unc_*), the standard deviation of the daily/monthly average ( StDv_*) for L2/L3 data, number of observations/days used for the daily/monthly average (NDays_*/NMeas_*) for L2/L3 data, and the percentage of missing measurements in the vertical ozone profile that made up the TrOC. More details about the availability and calculation of these uncertainties and percentage is also present in the README files summed up here above.

In addition to tropospheric ozone columns, CO and HCHO column are also provided from FTIR measurements, these species being well-known ozone precursors and, as such, can also be used within the scope of TOAR-II. These can be found in the directory FTIR on the HEGIFTOM ftp-server.