Articles | Volume 8, issue 24
Atmos. Chem. Phys., 8, 7737–7754, 2008
Atmos. Chem. Phys., 8, 7737–7754, 2008

  23 Dec 2008

23 Dec 2008

Lagrangian analysis of low altitude anthropogenic plume processing across the North Atlantic

E. Real1,*, K. S. Law1, H. Schlager2, A. Roiger2, H. Huntrieser2, J. Methven3, M. Cain3, J. Holloway4, J. A. Neuman4, T. Ryerson5, F. Flocke6, J. de Gouw4, E. Atlas7, S. Donnelly8, and D. Parrish5 E. Real et al.
  • 1Service d'Aéronomie/UPMC, CNRS-IPSL, 4 Place Jussieu, 75005 Paris, France
  • 2Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Institut für Physik der Atmosphäre, 82230 Wessling, Germany
  • 3Department of Meteorology, University of Reading, P.O. Box 243, Earley Gate, Reading, RG6 6BB, UK
  • 4NOAA ESRL/CIRES, University of Colorado at Boulder, Boulder CO 80309, USA
  • 5NOAA ESRL, 325 Brodway, Boulder, CO 80305 USA
  • 6Atmospheric Chemistry Division, NCAR, 1850 Table Mesa Drive Boulder, CO 80305 USA
  • 7RSMAS/MAC University of Miami, Miami, FL 33149 USA
  • 8Department of Chemistry, Fort Hays State University, Hays KS 67601 USA
  • *now at: CEREA, Paris Est, 20 rue Alfred Nobel 77455, Champs sur Marne, France

Abstract. The photochemical evolution of an anthropogenic plume from the New-York/Boston region during its transport at low altitudes over the North Atlantic to the European west coast has been studied using a Lagrangian framework. This plume, originally strongly polluted, was sampled by research aircraft just off the North American east coast on 3 successive days, and then 3 days downwind off the west coast of Ireland where another aircraft re-sampled a weakly polluted plume. Changes in trace gas concentrations during transport are reproduced using a photochemical trajectory model including deposition and mixing effects. Chemical and wet deposition processing dominated the evolution of all pollutants in the plume. The mean net photochemical O3 production is estimated to be −5 ppbv/day leading to low O3 by the time the plume reached Europe. Model runs with no wet deposition of HNO3 predicted much lower average net destruction of −1 ppbv/day O3, arising from increased levels of NOx via photolysis of HNO3. This indicates that wet deposition of HNO3 is indirectly responsible for 80% of the net destruction of ozone during plume transport. If the plume had not encountered precipitation, it would have reached Europe with O3 concentrations of up to 80 to 90 ppbv and CO between 120 and 140 ppbv. Photochemical destruction also played a more important role than mixing in the evolution of plume CO due to high levels of O3 and water vapour showing that CO cannot always be used as a tracer for polluted air masses, especially in plumes transported at low altitudes. The results also show that, in this case, an increase in O3/CO slopes can be attributed to photochemical destruction of CO and not to photochemical O3 production as is often assumed.

Final-revised paper