Accounting for non-linear chemistry of ship plumes in the GEOS-Chem global chemistry transport model

Abstract

Abstract. 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-ingrid 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 conCorrespondence to: G. C. M. Vinken (g.c.m.vinken@tue.nl) centrations 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 inplume chemistry is most relevant for pristine marine areas.

Model calculations of the effects of present and future emissions of air pollutants from shipping in the Baltic Sea and the North Sea

“…Model calculations with a parameterization of the ship plumes suggest that with this approach we overestimate NO x concentrations and ozone formation (Huszar et al, 2010;Vinken et al, 2011). Our results may not be directly comparable as we use a much finer horizontal model resolution.…”

“…Our results may not be directly comparable as we use a much finer horizontal model resolution. In addition Vinken et al (2011) find that the differences between the plume calculations and instant dilution are smallest over strongly polluted seas such as the North Sea. This suggests that implementing a parameterization of the ship plumes would not change our results significantly.…”

Sensitivity to grid resolution in the ability of a chemical transport model to simulate observed oxidant chemistry under high-isoprene conditions

“…Liang and Jacobson (2000) showed that premature mixing of urban and background air masses can lead to either overestimates or underestimates of OPE. Model simulations of ship plumes indicate particularly large ozone overestimates when mixing NO x from the plumes into otherwise clean grid cells (Davis et al, 2001;Vinken et al, 2011). On a global scale, Wild and Prather (2006) found from an asymptotic error convergence method that grid averaging in a 2.8 • × 2.8 • model caused a +4 % bias in the global tropospheric ozone burden, with larger errors on regional scales.…”

“…Model simulations of ship plumes indicate particularly large ozone overestimates when mixing NO x from the plumes into otherwise clean grid cells (Davis et al, 2001;Vinken et al, 2011). On a global scale, Wild and Prather (2006) found from an asymptotic error convergence method that grid averaging in a 2.8 • × 2.8 • model caused a +4 % bias in the global tropospheric ozone burden, with larger errors on regional scales. Ito et al (2009) compared global models of varying resolutions and concluded that artificial mixing of biogenic VOC emissions into coarse grid cells drives excessive conversion of NO x to organic nitrate reservoirs, leading to release of NO x downwind under higher OPE conditions and thereby causing excessive ozone production.…”

Evolving research directions in Surface Ocean - Lower Atmosphere (SOLAS) science

“…[109] Alternative attempts to address this have included a box model approach, [110] a large eddy model approach [116] and a ship plume parameterisation in a regional model. [117] A promising approach is the 'plume-in-grid' formulation by Vinken et al, [118] which, when incorporated in a global model, showed that ignoring these effects leads to overestimation of NO x and O 3 concentrations in the North Atlantic by 50 and 10-25 % respectively. Further work is clearly required to determine how grid-scale ship plumes can be parameterised in numerical models.…”