Ship-borne FTIR measurements of CO and O3 in the Western Pacific from 43° N to 35° S: an evaluation of the sources
Carbon monoxide (CO) and ozone (O3) have been measured in the Western Pacific (43° N to 35° S) during a ship campaign with Research Vessel Sonne in fall 2009. Observations have been performed using ship-based solar absorption Fourier Transform infrared spectrometry, flask sampling, balloon sounding, and in-situ Fourier Transform infrared analysis. The obtained results are compared to the GEOS-Chem global 3-D chemistry transport model for atmospheric composition. In general, a very good agreement is found between the GEOS-Chem model and all instruments. The CO and O3 distributions show a comparable variability suggesting an impact from the same source regions.
Tagged-CO simulations implemented in the GEOS-Chem model allow to differentiate between different sources and source regions. The sources are verified with HYSPLIT backward trajectory calculations. In the Northern Hemisphere fossil fuel combustion in Asia is the dominant source. European and North American fossil fuel combustion also contribute to Northern Hemispheric CO pollution. In the Southern Hemisphere contributions from biomass burning and fossil fuel combustion are dominant; African biomass burning has a significant impact on Western Pacific CO pollution. Furthermore, in the tropical Western Pacific enhanced upper tropospheric CO within the tropical tropopause layer mainly originates from Indonesian fossil fuel combustion and can be transported into the stratosphere.
The sources and source regions of the measured O3 pollution are simulated with a tagged-O3 simulation implemented in the GEOS-Chem model. Similar source regions compared to the tagged-CO simulations are identified by the model. In the Northern Hemisphere contributions from Asia, Europe, and North America are significant. In the Southern Hemisphere the impact of emissions from South America, South-East Africa, and Oceania is important.