Evidence from firn air for recent decreases in non-methane hydrocarbons and a 20th century increase in nitrogen oxides in the northern hemisphere

David R. Worton, William T. Sturges, Claire E. Reeves, Mike J. Newland, Stuart A. Penkett, Elliot Atlas, Verity Stroud, Kristen Johnson, Josef Norbert Schmidbauer, Sverre Solberg, Jakob Schwander, Jean-Marc Barnola