Shipping and the environment: Smokestack emissions, scrubbers and unregulated oceanic consequences

Introduction The use of fossil fuels as an energy source results in the emission of a complex mixture of gases, aerosols and particulate matter to the atmosphere. Legislation to limit these emissions has been implemented both on land and at sea in order to safeguard human health and the environment. However, such legislation began to be implemented earlier for land-based emissions than for emissions from commercial shipping, and the land-based legislation continues to be more restrictive than that for shipping. We address the development of sulphur oxide scrubber technology from a marine and atmospheric environment perspective, directions for future research, and also the options for assessing the consequences of ship plumes in the context of environmental monitoring programmes. Regulation of ship plume emissions The International Maritime Organisation (IMO), a body under the United Nations, has adopted the International Convention for the Prevention of Pollution from Ships (MARPOL), where Annex VI is concerned with air pollution from shipping (IMO, 2008a). This Annex regulates the emission of sulphur and nitrogen oxides (SOX and NOX) from smokestacks (Figure 1), together with emissions of halocarbons from refrigeration plants and emissions of volatile organic compounds from oil tankers. Two levels of regulation apply for SOX and NOX emissions: a global level; and a stricter level applied in Emission Control Areas (ECA). The title of the SOX regulation, no. 14 in IMO (2008a), also refers to particulate matter, but as there is no further explicit mention of particulate emissions, the emission reduction that is achieved is for sulphate aerosols only. However, extended regulation of particulate matter is under current investigation (Lack et al., 2012). Other smokestack emissions including all types of particulate matter, organic compounds such as polycyclic aromatic hydrocarbons (PAHs), and metals are not yet regulated by Annex VI. Regulation of metal concentrations in scrubber washwater has been proposed to the IMO (IMO, 2007), but the current guidelines merely state that “The washwater treatment system should be designed to minimize RESEARCH ARTICLE