The Diesel fuel quality has been a trending topic of lately especially in relation to the power generation. Fuel quality can be affected at many different points before and after it is delivered to power the equipment and for generation purposes. Water is one of the greatest enemies of the diesel fuel. However, in this article we are going to focus on another culprit, Sulphur. The Sulphur (S) content of diesel fuel is a closely monitored quantity in assessing the fuel quality. There are few applications like road, non-road (power generation), maritime, and locomotive where the sulphur content in diesel is related to.
Many developed countries are using Ultra-low-sulfur diesel (ULSD) which is the diesel fuel with substantially lowered sulfur content. ULSD with a maximum sulphur content of 15 ppm has been the norm for road vehicles in USA since year 2006. Studies done in USA confirmed the emission benefits accrued from reducing sulfur from 450 to 50 ppm based on the research leading up to that point in 1993 . Following that they further investigated the benefits of reducing it all the way down to 10 ppm. EPA has conducted several studies to investigate sulfurs effect on emissions since then and the limit of 15 ppm has been an outcome of these extensive studies. Furthermore, non-road Diesel fuel standards were also strengthened limiting to 15 ppm in 2010 and by the year 2014, all non-road, locomotive, and marine sectors had to adhere to the same standard.. Looking at Europe, it imposed a 150 ppm limit in 200 and a 50 ppm limit in 2005 . “Member States and the Commission should take appropriate steps to facilitate the placing on the market of gasoil containing 10 ppm sulphur earlier than 1 January 2011” states the "DIRECTIVE 2009/30/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL" . This was intended for the EURO V standards. The EURO 6 standards intend to continue at this limit for the heavy-duty vehicles. 
Focussing on the developing nations, China has recently lowered the sulphur in Diesel to 150 ppm as of late. This is equivalent to a Euro III standard. By year 2017, India requires on-road diesel and gasoline nationwide to meet BS IV specifications with a maximum limit of 50 ppm. A recent article confirmed New Delhi becoming the first city in India to be running on BS-VI fuels . India intends to further reduce this to a 15 ppm maximum limit by 2020. There are also reports from few countries in Africa already using 50 ppm Diesel. After a directive from UN Nigeria will lower the top level in sulfur from a staggering 3000 ppm. These improvements in fuel standards will lead to reduced harm from emissions. This review is the first step of assessing the progress of states shifting towards low sulphur Diesel in all applications.
 Fuel Sulphur Effects on Exhaust Emissions: Recommendations for MOBILE6 HERE