Accounting for non-linear chemistry of ship plumes in the GEOS-Chem global chemistry transport model
We present a computationally efficient approach to account for the non-linear chemistry occurring during the dispersion of ship exhaust plumes in a global 3-D model of atmospheric chemistry (GEOS-Chem). We use a plume-in-grid formulation where ship emissions age chemically for 5 h before being relea...
| Published in: | Atmospheric Chemistry and Physics |
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| Main Authors: | , , , |
| Format: | Text |
| Language: | English |
| Published: |
2018
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/acp-11-11707-2011 https://www.atmos-chem-phys.net/11/11707/2011/ |
| Summary: | We present a computationally efficient approach to account for the non-linear chemistry occurring during the dispersion of ship exhaust plumes in a global 3-D model of atmospheric chemistry (GEOS-Chem). We use a plume-in-grid formulation where ship emissions age chemically for 5 h before being released in the global model grid. Besides reducing the original ship NO x emissions in GEOS-Chem, our approach also releases the secondary compounds ozone and HNO 3 , produced during the 5 h after the original emissions, into the model. We applied our improved method and also the widely used "instant dilution" approach to a 1-yr GEOS-Chem simulation of global tropospheric ozone-NO x -VOC-aerosol chemistry. We also ran simulations with the standard model (emitting 10 molecules O 3 and 1 molecule HNO 3 per ship NO x molecule), and a model without any ship emissions at all. The model without any ship emissions simulates up to 0.1 ppbv (or 50%) lower NO x concentrations over the North Atlantic in July than our improved GEOS-Chem model. "Instant dilution" overestimates NO x concentrations by 0.1 ppbv (50%) and ozone by 3–5 ppbv (10–25%), compared to our improved model over this region. These conclusions are supported by comparing simulated and observed NO x and ozone concentrations in the lower troposphere over the Pacific Ocean. The comparisons show that the improved GEOS-Chem model simulates NO x concentrations in between the instant dilution model and the model without ship emissions, which results in lower O 3 concentrations than the instant dilution model. The relative differences in simulated NO x and ozone between our improved approach and instant dilution are smallest over strongly polluted seas (e.g. North Sea), suggesting that accounting for in-plume chemistry is most relevant for pristine marine areas. |
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