Pros and cons of low sulfur fuel

Lower sulfur fuel is expected to reduce deaths and illness from small particulate matter, but its use could also contribute to global warming.    New global standards proposed by the International Maritime Organization to reduce the maximum sulfur content in ship fuel to 0.5 percent (by mass) after Jan. 1, 2020 from the current global cap of 3.5 percent will reduce deaths and illness related to fine particle emissions, according to a paper titled, “Cleaner fuels for ships provide public health benefits with climate tradeoffs,” which was published in the scientific journal Nature Communications.
   “Cleaner marine fuels will reduce ship-related premature mortality and morbidity by 34 percent and 54 percent, respectively,” the paper said. That represents a 2.6 percent reduction in deaths globally from cardiovascular disease and lung cancer related to fine particles 2.5 micrometers in diameter or smaller (PM2.5), and a 3.6 percent global reduction in childhood asthma.
   Despite these reductions, the paper said low-sulfur marine fuels will still account for approximately 250,000 deaths and 6.4 million childhood asthma cases annually.
   “More stringent standards beyond 2020 may provide additional health benefits,” according to the paper.
   However, it argued how the new fuel standards could be bad for the effort to combat global warming by reducing “radiative cooling from ship aerosols by approximately 80 percent.”
   “Therefore, stronger international shipping policies may need to achieve climate and health targets by jointly reducing greenhouse gases and air pollution,” the paper said.
   A 2009 paper titled, “Shipping Emissions: From Cooling to Warming of Climate—and Reducing Impacts on Health” in Environmental Science Technology explained particles formed from the sulfur dioxide (SO₂) emitted by ship engines “have a direct impact on climate by scattering solar radiation and thus reducing the amount of shortwave radiation heating of the surface.” It added the SO₂ indirectly affects climate by increasing the reflectance and lifetimes of clouds.
   “This contribution is significant because ships emit in regions with a clean environment and frequent low clouds,” it said. “The potential impact of particulate matter due to shipping emissions is larger… given the relative albedo (reflectivity of light) change over a dark ocean, as opposed to similar emissions over more reflective land surfaces.”
   On the other hand, the paper in Nature Communications noted how “2020 compliant fuels may enable or be accompanied with other PM2.5 emission reductions, such as organic carbon particles and black carbon particles, which contribute to strongly warming effects. Moreover, many control technologies for harmful particulates and ozone precursor emissions perform better under low-sulfur combustion conditions.”
   Lower sulfur fuel is likely to be much more expensive than current bunker fuel. An article last week by Platts said, “Some in the bunker industry have forecast 0.5 percent sulfur bunker prices could be as much as $400 per metric ton more expensive than conventional fuel oil in 2020.” It added that may give shipowners a motive to break the rules requiring the use of low sulfur fuel. There are also concerns about whether refineries will be able to produce enough low sulfur fuel.