## 5 Annex: Black Carbon Definition and Measurement Issues  
A landmark study [26] of black carbon notes that 'The strong absorption of visible light at all visible wave lengths by black carbon is the distinguishing characteristic that has raised interest in studies of atmospheric radiative transfer. No other substance with such strong light absorption per unit mass is present in the atmosphere in significant quantities.' Black carbon (BC) is sometimes equated to soot, but that is not accurate. Black carbon is one component of soot, which is the black smoke that appears when fossil fuels and biofuels burn. The other components of soot, as co-pollutants with BC, include organic carbon (OC), sulphur oxide (SOx), nitrous oxide NOx), and ozone. A secondary emission ozone occurs as a result of interactions of elements in the soot, including black carbon. The amount of BC in diesel exhaust is especially notable in the context of the present article because the ratio of BC to OC is centrally important to an understanding of the effects on climate change of emissions of these co-pollutants in ships' emissions. The reason is that OC is a global _coolant_. The BC:OC ratio varies across sources. At one extreme, heavy duty diesel engines have a relatively high BC:OC ratio and are thus potent global warming agents. Since not all diesel engines are the same, it is necessary to consider the type of application in order to obtain a precise indication of the BC:OC ratio. Large marine engines have been reported to have a BC:OC ratio as high as 9 [28]. In studies of elemental carbon (EC), which is highly correlated with BC though not chemically quite the same, for US on-road heavy-duty diesel vehicles, the EC:OC ratio was found to be 4.4 [86]. In the same study, the ratio for on-road light-duty vehicles the ratio was 1.5. The consistent core finding is that the net of warming over cooling agents was greater than 1, and usually much greater. Similar patterns have been found for non-road diesel and locomotive diesel engines in the US [86]. Commonly used numbers about the levels of emissions of GHGs and/or BC are not indicative of the full extent of the consequences of BC emissions for climate change, human health, or food production. (1) Numbers that indicate levels of greenhouse gas emissions singly or as a collective CO2e do not include BC. (2) BC numbers for global emissions do not reflect three important regional facts about the emissions: (a) BC emissions are disproportionately concentrated in densely populated urban areas in Italy and other countries and thus affect human health more than global numbersimply. (b) Shipping's emissions are particularly damaging to human health and food production along coastal shipping routes. (c) BC emissions in the Arctic region are more impactful than carbon dioxide emissions and thus contribute disproportionately to the Arctic's temperature increase, which is more than twice as much as the global average as a result of BC, CO\({}_{2}\), and other greenhouse gasses. A formal definition of black carbon follows [24]: 'Black carbon is a distinct type of carbonaceous material, formed only in flames during combustion of carbon-based fuels. It is distinguishable from other forms of carbon and carbon compounds contained in atmospheric aerosol because it has a unique combination of the following physical properties: 1. It strongly absorbs visible light with a mass absorption cross-section of at least 5 m\({}^{2}\) g\({}^{-1}\) at a wavelength of 550 nm. 2. It is refractory; that is, it retains its basic format at very high temperatures, with a vaporization temperature near 4000K. 3. It is insoluble in water, in organic solvents including methanol and acetone, and in other components of atmospheric aerosol. 4. It exists as an aggregate of small carbon spherules. The following are available online at [[http://www.mdpi.com/2076-3417/10/23/8544/s1](http://www.mdpi.com/2076-3417/10/23/8544/s1)]([http://www.mdpi.com/2076-3417/10/23/8544/s1](http://www.mdpi.com/2076-3417/10/23/8544/s1)).