Copyright 2007 by the American Geophysical Union.Schoeberl, M. R.Ziemke, J. R.Bojkov, B.Livesey, N.Duncan, B.Strahan, S.Froidevaux, L.Kulawik, S.Bhartia, P. K.Chandra, S.Levelt, P. F.Witte, J. C.Thompson, A. M.Cuevas, E.Redondas, A.Tarasick, D. W.Davies, J.Bodeker, G.Hansen, G.Johnson, B. J.Oltmans, S. J.Vömel, H.Allaart, M.Kelder, H.Newchurch, M.Godin Beekmann, S.Ancellet, G.Claude, H.Andersen, S. B.Kyrö, E.Parrondo, María ConcepciónYela González, MargaritaZablocki, G.Moore, D.Dier, H.Von der Gathen, P.Viatte, P.Stübi, R.Calpini, B.Skrivankova, P.Dorokhov, V.De Backer, H.Schmidlin, F. J.Coetzee, G.Fujiwara, M.Thouret, V.Posny, F.Morris, G.Merrill, J.Leong, C. P.Koenig Langlo, G.Joseph, E.2026-01-222026-01-222007-12-19Journal of Geophysical Research: Atmospheres 112(D24): D24S492169-8996https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007JD008773https://hdl.handle.net/20.500.12666/1661Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.[1] We estimate the tropospheric column ozone using a forward trajectory model to increase the horizontal resolution of the Aura Microwave Limb Sounder (MLS) derived stratospheric column ozone. Subtracting the MLS stratospheric column from Ozone Monitoring Instrument total column measurements gives the trajectory enhanced tropospheric ozone residual (TTOR). Because of different tropopause definitions, we validate the basic residual technique by computing the 200-hPa-to-surface column and comparing it to the same product from ozonesondes and Tropospheric Emission Spectrometer measurements. Comparisons show good agreement in the tropics and reasonable agreement at middle latitudes, but there is a persistent low bias in the TTOR that may be due to a slight high bias in MLS stratospheric column. With the improved stratospheric column resolution, we note a strong correlation of extratropical tropospheric ozone column anomalies with probable troposphere-stratosphere exchange events or folds. The folds can be identified by their colocation with strong horizontal tropopause gradients. TTOR anomalies due to folds may be mistaken for pollution events since folds often occur in the Atlantic and Pacific pollution corridors. We also compare the 200-hPa-to-surface column with Global Modeling Initiative chemical model estimates of the same quantity. While the tropical comparisons are good, we note that chemical model variations in 200-hPa-to-surface column at middle latitudes are much smaller than seen in the TTOR.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttps://creativecommons.org/licenses/by-nc-nd/4.0/tropospheric ozonepollutionair qualityinfo:eu-repo/semantics/article10.1029/2007JD0087732169-897Xinfo:eu-repo/semantics/openAccess