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

Abstract

Abstract. Elevated levels of formaldehyde (HCHO) along the ship corridors have been observed by satellite sensors, such as ESA/ERS-2 GOME (Global Ozone Monitoring Experiment), and were also simulated by global 3-D chemistrytransport models. In this study, three likely sources of the elevated HCHO levels in the ship plumes as well as their contributions to the elevated HCHO levels (budget) were investigated using a newly-developed ship-plume photochemical/dynamic model: (1) primary HCHO emission from ships; (2) secondary HCHO production via the atmospheric oxidation of non-methane volatile organic compounds (NMVOCs) emitted from ships; and (3) atmospheric oxidation of CH 4 within the ship plumes. For this ship-plume modelling study, the ITCT 2K2 (Intercontinental Transport and Chemical Transformation 2002) ship-plume experiment, which was carried out about 100 km off the coast of California on 8 May 2002 (11:00 local standard time), was chosen as a base study case because it is the best defined in terms of (1) meteorological data, (2) in-plume chemical composition, and (3) background chemical composition. From multiple shipplume model simulations for the ITCT 2K2 ship-plume experiment case, CH 4 oxidation by elevated levels of in-plume OH radicals was found to be the main factor responsible for the elevated levels of HCHO in the ITCT 2K2 ship-plume. More than ∼88% of the HCHO for the ITCT 2K2 ship-plume is produced by this atmospheric chemical process, except in Correspondence to: C. H. Song (chsong@gist.ac.kr) the areas close to the ship stacks where the main source of the elevated HCHO levels would be primary HCHO from the ships (due to the deactivation of CH 4 oxidation from the depletion of in-plume OH radicals). Because of active CH 4 oxidation by OH radicals, the instantaneous chemical lifetime of CH 4 (τ CH 4 ) decreased to ∼0.45 yr inside the ship plume, which is in contrast to τ CH 4 of ∼1.1 yr in the background (up to ∼41% decrease) for the ITCT 2K2 ship-plume case. A variety of likely ship-plume situations at three different latitudinal locations within the global ship corridors was also studied to determine the enhancements in the HCHO levels in the marine boundary layer (MBL) influenced by ship emissions. It was found that the ship-plume HCHO levels could be 19.9-424.9 pptv higher than the background HCHO levels depending on the latitudinal locations of the ship plumes (i.e., intensity of solar radiation and temperature), MBL stability and NO x emission rates. On the other hand, NMVOC emissions from ships were not found to be a primary source of photochemical HCHO production inside ship plumes due to their rapid and individual dilution. However, the diluted NMVOCs would contribute to the HCHO productions in the background air.

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

“…To structure the discussion of the results, we separate the plume dispersion in three regimes, as proposed by Song et al (2003) The strong decline in the O 3 concentrations during the first stage is caused by the O 3 being titrated by the abundantly available NO via Reaction (R3). Almost all O 3 within the plume is gone at this point, but stored as NO 2 and will later be recycled.…”

“…Franke et al, 2008;Kim et al, 2009;Song et al, 2010). These lateral and vertical dispersion parameters depend on the meteorological stability class and can be tuned in PARANOX.…”

“…In this study we follow an approach for the lateral and vertical dispersion in the lower troposphere originally described by Hanna et al (1985) (Offshore and Coastal Dispersion algorithm), adapted for dispersion calculations over water by Song et al (2003) and commonly used to describe ship plume dispersion (e.g. Franke et al, 2008;Kim et al, 2009;Song et al, 2010).…”

“…Several studies with Lagrangian models (e.g. von Song et al, 2003;Chen et al, 2005) showed that the NO x lifetime within ship plumes is a factor 2.5-10 shorter than the lifetime of roughly 1 day estimated by the instantly diluting CTMs. These Lagrangian models account for the higher NO x concentrations in the initial dispersion stages of the plume, leading to elevated OH levels and thereby shorter NO x lifetimes.…”

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

“…Elevated levels of formaldehyde (HCHO) in ship plumes detected by satellite [104] are probably attributable to enhanced oxidation of methane caused by elevated OH concentrations. [120] A robust assessment of these effects requires global models that include multispecies chemistry with realistic reaction rates.…”