Long-term changes in lower tropospheric baseline ozone concentrations at northern mid-latitudes - Parrish, D. D.; Law, K. S.; Staehelin, J.; Derwent, R.; Cooper, O. R.; Tanimoto, H.; Volz-Thomas, A.; Gilge, S.; Scheel, H.-E.; Steinbacher, M.; Chan, E. (Atmos. Chem. Phys., 2012)