Constraints on ship NO<sub>x</sub> emissions in Europe using GEOS-Chem and OMI satellite NO<sub>2</sub> observations

Abstract

Abstract. We present a top-down ship NO x emission inventory for the Baltic Sea, the North Sea, the Bay of Biscay and the Mediterranean Sea based on satellite-observed tropospheric NO 2 columns of the Ozone Monitoring Instrument (OMI) for [2005][2006]. We improved the representation of ship emissions in the GEOS-Chem chemistry transport model, and compared simulated NO 2 columns to consistent satellite observations. Relative differences between simulated and observed NO 2 columns have been used to constrain ship emissions in four European seas (the Baltic Sea, the North Sea, the Bay of Biscay and the Mediterranean Sea) using a mass-balance approach, and accounting for nonlinear sensitivities to changing emissions in both model and satellite retrieval. These constraints are applied to 39 % of total top-down European ship NO x emissions, which amount to 0.96 Tg N for 2005, and 1.0 Tg N for 2006 (11-15 % lower than the bottom-up EMEP ship emission inventory). Our results indicate that EMEP emissions in the Mediterranean Sea are too high (by 60 %) and misplaced by up to 150 km, which can have important consequences for local air quality simulations. In the North Sea ship track, our top-down emissions amount to 0.05 Tg N for 2005 (35 % lower than EMEP). Increased top-down emissions were found for the Baltic Sea and the Bay of Biscay ship tracks, with totals in these tracks of 0.05 Tg N (131 % higher than EMEP) and 0.08 Tg N for 2005 (128 % higher than EMEP), respectively. Our study explicitly accounts for the (non-linear) sensitivity of satellite retrievals to changes in the a priori NO 2 profiles, as satellite observations are never fully independent of model information (i.e. assumptions on vertical NO 2 profiles). Our study provides for the first time a space-based, top-down ship NO x emission inventory, and can serve as a framework for future studies to constrain ship emissions using satellite NO 2 observations in other seas.

The impact of shipping emissions on air pollution in the greater North Sea region – Part 1: Current emissions and concentrations

“…Even if the areas are not the same, the differences seem to be remarkable. Recent investigations by Vinken et al (2014) using satellite data suggested that the officially reported ship emissions might be overestimated by about 35 %. In 2015, EMEP revised the emissions provided through their website to 644 Gg for NO x and 162 Gg for SO 2 (EMEP/CEIP, 2015).…”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Optimisation of the emissions of several other compounds have also been evaluated through inverse methods constrained by satellite observations, such as isoprene, methanol or formaldehyde (Stavrakou et al, 2011(Stavrakou et al, , 2009Palmer et al, 2003;Wells et al, 2014;Barkley et al, 2013), and other studies have focused on the optimisations of the emissions from different sectors, such as ships (de Ruyter de Wildt et al, 2012;Vinken et al, 2014).…”

Evaluation of OMI operational standard NO<sub>2</sub> column retrievals using in situ and surface-based NO<sub>2</sub> observations

“…NO 2 observations from satellite offer a globally consistent data set, albeit at coarse resolutions of 10 s to 100 s of kilometers, enabling a wide range of applications including many not feasible from in situ observations. Several studies have used satellite observations of NO 2 to evaluate chemical transport models (Martin et al, 2002;van Noije et al, 2006;Lamsal et al, 2008;Kim et al, 2009;Herron-Thorpe et al, 2010;Huijnen et al, 2010), examine spatial and temporal patterns of NO x emissions (Beirle et al, 2003;Richter et al, 2005;Kim et al, 2006;van der A et al, 2006;Zhang et al, 2007;Boersma et al, 2008a;Lu and Streets, 2012;Wang et al, 2012;Hilboll et al, 2013;Russell et al, 2010Russell et al, , 2012Duncan et al, 2013), examine NO x sources (Jaeglé et al, 2005;van der A et al, 2008;Bucsela et al, 2010;de Wildt et al, 2012;Lin, 2012;Ghude et al, 2010Ghude et al, , 2013aMebust et al, 2011;Mebust and Cohen, 2013), provide top-down constraints on surface NO x emissions Konovalov et al, 2006;Zhao and Wang, 2009;Lin et al, 2010;Lamsal et al, 2011;Ghude et al, 2013b;Vinken et al, 2014), infer NO x lifetimes (Schaub et al, 2007;Lamsal et al, 2010;Beirle et al, 2011), and estimate surface NO 2 concentrations …”