The impact of traffic emissions on atmospheric ozone and OH: results from QUANTIFY
1Max Planck Institute for Chemistry, Dept. of Atmospheric Chemistry, 55020 Mainz, Germany
2Transportation Studies, German Aerospace Center (DLR), Berlin, Germany
3Laboratoire des Sciences du Climat et de l'Environment (LSCE), CEN de Saclay, Gif-sur-Yvette, France
4Centre for Atmospheric Science, Dept. of Chemistry, Cambridge, UK
5DNV, Det Norske Veritas (DNV), Oslo, Norway
6Dept. of Geosciences, University of Oslo, Norway
7Deutsches Zentrum für Luft- und Raumfahrt, Inst. für Physik der Atmosphäre, Oberpaffenhofen, 82234 Wessling, Germany
8Center for International Climate and Environmental Research-Oslo (CICERO), Oslo, Norway
9Royal Netherlands Meteorological Institute, KNMI, De Bilt, The Netherlands
10Meteo France, CNRS, Toulouse, France
11Department of Earth System Science, University of California, Irvine, USA
12Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology, Zürich, Switzerland
13Department of Meteorology, University of Reading, UK
14Joint Research Center, JRC, Ispra, Italy
Abstract. To estimate the impact of emissions by road, aircraft and ship traffic on ozone and OH in the present-day atmosphere six different atmospheric chemistry models have been used. Based on newly developed global emission inventories for road, ship and aircraft emission data sets each model performed sensitivity simulations reducing the emissions of each transport sector by 5%.
The model results indicate that on global annual average lower tropospheric ozone responds most sensitive to ship emissions (50.6%±10.9% of the total traffic induced perturbation), followed by road (36.7%±9.3%) and aircraft exhausts (12.7%±2.9%), respectively. In the northern upper troposphere between 200–300 hPa at 30–60° N the maximum impact from road and ship are 93% and 73% of the maximum effect of aircraft, respectively. The latter is 0.185 ppbv for ozone (for the 5% case) or 3.69 ppbv when scaling to 100%. On the global average the impact of road even dominates in the UTLS-region. The sensitivity of ozone formation per NOx molecule emitted is highest for aircraft exhausts.
The local maximum effect of the summed traffic emissions on the ozone column predicted by the models is 0.2 DU and occurs over the northern subtropical Atlantic extending to central Europe. Below 800 hPa both ozone and OH respond most sensitively to ship emissions in the marine lower troposphere over the Atlantic. Based on the 5% perturbation the effect on ozone can exceed 0.6% close to the marine surface (global zonal mean) which is 80% of the total traffic induced ozone perturbation. In the southern hemisphere ship emissions contribute relatively strongly to the total ozone perturbation by 60%–80% throughout the year.
Methane lifetime changes against OH are affected strongest by ship emissions up to 0.21 (± 0.05)%, followed by road (0.08 (±0.01)%) and air traffic (0.05 (± 0.02)%).
Based on the full scale ozone and methane perturbations positive radiative forcings were calculated for road emissions (7.3±6.2 mWm−2) and for aviation (2.9±2.3 mWm−2). Ship induced methane lifetime changes dominate over the ozone forcing and therefore lead to a net negative forcing (−25.5±13.2 mWm−2).