Dispersion and chemical evolution of ship plumes in the marine boundary layer: Investigation of O₃/NO_y/HO_x chemistry

Abstract

[1] The dispersion and chemical evolution of NO x in ship plumes has been investigated for marine boundary layer (MBL) conditions. This effort has involved combining a plume dispersion algorithm with a time-dependent photochemical box model. The analysis has considered several factors, all of which can influence the net impact of NO x on the background environment. These include the following: season of the year, latitude of point of release, meteorological setting, and ship NO x emission rate. Reaction rates within a plume were shown to be a nonlinear function of the levels of NO x , leading to relative estimates of ship plume NO x lifetimes that were factors of 2.5-10 times shorter than for ambient marine conditions. The shortened ship-plume NO x lifetime reflects both elevated daytime levels of OH and nighttime levels of NO 3 and N 2 O 5 , all of which were estimated to be several times larger than those typical of ambient marine conditions. During daylight hours, elevated ship plume OH resulted in the net photochemical production of O 3 , with peak concentrations being 5-65% higher than background values, depending on latitude. The areal integrated O 3 effect, however, is estimated to be quite small due to further plume dilution. In addition, because of the shorter estimated lifetime for NO x , it would seem reasonable that the integrated O 3 production from the current Lagrangian modeling effort would be significantly lower than that predicted by global 3-D grid models. The current predicted shortened lifetime for NO x is quite significant in terms of assessing a ship plume's impact on background marine levels of NO x . In fact, these results would seem to explain a significant fraction of the overprediction of NO x levels in and near shipping lanes recently estimated using 3-D Eulerian global models.

Source identification and budget analysis on elevated levels of formaldehyde within the ship plumes: a ship-plume photochemical/dynamic model analysis

“…The CH 4 and NMVOC oxidation rates are controlled mainly by the levels of OH radicals, which were found to be a function of the stability class of the MBL (Song et al, 2003a;Kim et al, 2009). Moreover, the OH radical mixing ratios are a strong function of other meteorological variables, such as solar radiation, relative humidity and temperature (Song et al, 2003a, b).…”

“…In brief, the model has two fundamental components to treat: (1) atmospheric thermo-chemical, photo-chemical and heterogeneous reactions; and (2) turbulent dispersion of air pollutants emitted from a ship. For the latter, a "Gaussianbased" scheme for considering the horizontal and vertical turbulent dispersions of primary pollutants, such as SO 2 and NO x , was adopted from the Offshore and Coastal Dispersion (OCD) model with some modifications (Hanna et al, 1985;Song et al, 2003a;Kim et al, 2009). In particular, several turbulent ship-plume dispersion schemes within the MBL were reviewed by Faloona (2009).…”

“…Frick and Hoppel, 2000;Song et al, 2003a). Therefore, three stability classes (instead of the two stability classes for the base case study) were considered in the ship-plume photochemical/dynamic modelling for the constructed cases at different latitudinal locations: (1) neutral (D); (2) moderately stable (E); and (3) stable (F) MBL stability classes.…”

“…However, in their study, 3-D grid-based CTM simulations were carried out, which by-passed the complex and nonlinear ship-plume photochemistry. According to Song et al (2003a) and von Glasow et al (2003), by-passing the nonlinear ship-plume photochemistry can result in overestimated O 3 , OH and NO x mixing ratios in the 3-D grid-based CTM simulations. In this sense, the rates of CH 4 destruction calculated by Hoor et al (2009) could be overestimated.…”

“…Until now, many detailed analyses of the impacts of ocean-going ship emissions on atmospheric MBL chemistry and the global radiation budget have been carried out in a range of aspects: (1) O 3 /HO x /NO y photochemistry in the MBL (e.g., Lawrence and Crutzen, 1999;Endresen et al, 2003;Song et al, 2003a;von Glasow et al, 2003;Kim et al, 2009); (2) sulfur cycle in the MBL (e.g., Capaldo et al, 1999;Song et al, 2003b;Faloona, 2009); and (3) impacts on the global radiation budget (e.g., Capaldo et al, 1999;Endresen et al, 2003;Langley et al, 2010).…”