Ship emitted NO2 in the Indian Ocean: comparison of model results with satellite data
1University of Bremen, Institute for Environmental Physics, Bremen, Germany
2Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
3Max Planck Institute for Chemistry, Mainz, Germany
Abstract. An inventory of NOx emission from international shipping has been evaluated by comparing NO2 tropospheric columns derived from the satellite instruments SCIAMACHY (January 2003 to February 2008), GOME (January 1996 to June 2003), and GOME-2 (March 2007 to February 2008) to NO2 columns calculated with the atmospheric chemistry general circulation model ECHAM5/MESSy1 (January 2000 to October 2005). The data set from SCIAMACHY yields the first monthly analysis of ship induced NO2 enhancements in the Indian Ocean. For both data and model consistently the tropospheric excess method was used to obtain mean NO2 columns over the shipping lane from India to Indonesia, and over two ship free regions, the Bay of Bengal and the central Indian Ocean. In general, the model simulates the differences between the regions affected by ship pollution and ship free regions reasonably well. Minor discrepancies between model results and satellite data were identified during biomass burning seasons in March to May over India and the Indochinese Peninsula and August to October over Indonesia. We conclude that the NOx ship emission inventory used in this study is a good approximation of NOx ship emissions in the Indian Ocean for the years 2002 to 2007. It assumes that around 6 Tg(N) yr−1 are emitted by international shipping globally, resulting in 90 Gg(N) yr−1 in the region of interest when using Automated Mutual Assistance Vessel Rescue System (AMVER) or 72 Gg(N) yr−1 when using the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) as spatial proxy. The results do not support some previously published lower ship emissions estimates of 3–4 Tg(N) yr−1 globally, making this study the first that evaluates atmospheric response to NOx ship emission estimates from space.