1. a NOAA Earth System Research Laboratory , Chemical Sciences Division , Boulder , CO , 80305 , USA
2. b Cooperative Institute for Research in Environmental Science, University of Colorado , Boulder , CO , 80309 , USA
3. c Department of Physics , Imperial College London , London , SW7 2AZ , UK
4. d Laboratoire Eau Environnement Systèmes Urbains , École Nationale des Ponts-Paris Tech, Université de Paris-Est , 77455 Cedex 02, France
5. e Department of Physics , McGill University , Montréal , QC , Canada , H3A 2T8
6. f Centre GEOTOP UQAM-McGill Université du Québec à Montréal , Montréal , QC , Canada , H3C 3P8