Particulates are pesky things that come in many different guises. Coarse varieties, visible in smoke, are an irritant for lungs and eyes. Finer particulates are possibly worse, as they can enter your bloodstream via your lungs. A large body of research has linked inhalation of particulate matter (PM) to respiratory illness and heart problems, and possibly other life-shortening diseases. Increasingly, the response to research linking PM to premature deaths is the introduction of regulations to curb air pollution.

One variety of PM has been singled out for particular attention; black carbon (BC), often referred to as soot. Like all PM varieties, BC is bad for human health, but one key attribute makes it the black sheep of the particulate family; it is light-absorbing. Suspended in the atmosphere it warms by absorbing sunlight, while soot deposits will make ice and snow melt faster. BC is therefore associated with global warning, especially in the polar regions.

The International Maritime Organization (IMO) began discussing BC in 2010, when it was informed that although marine vessels emit only around 2% of total global BC, the release of BC emissions in northern shipping routes affecting the Arctic is particularly damaging and magnifies their impact. In July 2011, the IMO agreed to initiate work to control BC emissions from shipping.

Progress has been slow. Some would say the IMO is moving with glacial speed on this issue, perhaps being held up by those questioning the case for regulating BC from shipping. But glaciers and Arctic sea ice have been receding at an alarming rate, opening up the region for more shipping activity, suggesting that pressure to regulate BC will grow.

So far, the IMO has not even agreed on a definition of BC that is suitable for developing a ship-specific regulation, or measurement methods. Should they count just the black sheep, or include brown and grey ones as well?

There are also diverging views on what has the biggest impact on BC emissions, a product of incomplete fuel combustion. Most - but not all - studies suggest that BC is linked to fuel quality, with low sulphur distillate fuels being better than heavy fuel oil (HFO). Uncertainty remains about the exact relationships between engine load and BC emissions, which will also vary between ship and engine types.

Several control measures have already been suggested, including vessel speed reduction, banning the use of HFO in or near the Arctic, designating a new emission control area (ECA) and technology solutions. These include in-engine measures, water-in-fuel emulsification and scrubbers. Diesel particulate filters are said to be particularly effective at controlling BC, but they work best with ultra low sulphur distillate fuels and cannot be used together with HFO.

Regulations of BC could be another assault on the use of HFO in international shipping, unless advocates of scrubbing technology can convince decision makers at the IMO that this is an appropriate BC control method.

A regulation for BC could also be the first targeting PM specifically. Actual PM limits are currently not specified in ECAs, as PM emissions (by mass) are reduced as a result of sulphur reductions.

The black sheep of the particulate family could be worth watching, as measures to control them might have an impact on the rest of the flock.

This text first appeared as a Commentary in the March/April 2013 issue of the Bunker Bulletin, the bi-monthly Bunkerworld magazine.