Increasing springtime ozone mixing ratios in the free troposphere over western North America

Owen R. Cooper, David D. Parrish, Andreas Stohl, Michael Trainer, Philippe Nédélec, Valérie Thouret, Jean Pierre Cammas, Samuel J. Oltmans, Bryan J. Johnson, David Tarasick, Thierry Leblanc, Stuart McDermid, Dan Jaffe, Rushan Gao, Jeff Stith, Tom Ryerson, Kenneth Aikin, Teresa Campos, Andrew Weinheimer, Melody A. Avery