Aerosols & Shipping
Cutting emissions
Air pollution is a severe issue that threatens the health of humans, animals, and the environment. Aerosol pollution, especially from sulfates, contributes to respiratory, cardiovascular, and lung disease.1 The effects of air pollution on human health is most significant in coastal port cities due to sulfur present in ship fuel which contributes to a high concentration of sulfate aerosols. It is estimated that the high sulfur content of marine fuel contributes to between 19 000 and 91 000 premature deaths each year in coastal regions from respiratory and other diseases they cause.2 The environment is also impacted by the emission of these sulfur-rich fuels from ships as it can lead to acid rain which negatively impacts crops, forests and aquatic species.1 Aerosols can also decrease the amount of precipitation from summer monsoons in Africa and Asia, impacting agriculture and food supply.3
In recent years, the International Maritime Organization (IMO) has gotten more serious about cutting sulfur emissions from ships. Their new rule, enforced on January 1, 2020, limits the sulfur content in the fuel oil used on board ships. The restriction lowers the amount of sulfur allowed in fuel oil from 3.5% to 0.50% m/m (mass by mass).1 The image below is a summary of the IMO’s goals in reducing the sulfur content of ship fuel.
In 2023, it was found that SO2 emissions had dropped by 10% already.2 Yet, some unintended consequences may have arisen from these restrictions. It has been proposed that a drop in SO2 concentrations as a result of the IMO regulations may have played a role in the recent spike in global sea surface temperature.2
More research is required, and it is clear that there are several other contributors to the decrease in aerosol concentration. Still, aerosols do have an important role to play in climate regulation. Why would a drop in SO2 or other aerosol concentrations lead to an increase in temperature? Let’s look at the chemistry to find out.