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Reducing sulfur in transportation fuels provides immediate near-term emission reductions to improve air quality and mitigate climate change by reducing emissions from the existing, on-road fleet. Longer-term benefits are obtained with the implementation of complementary emission standards for all new and in-use vehicles. Black carbon and PM2.5 associated with diesel combustion can be controlled using diesel particulate filters required by soot-free emission standards like Euro 6/VI or U.S. 2010, but these devices are only effective with low, or ideally ultralow, sulfur fuels.
Fuel-importing countries can shift relatively quickly to low-sulfur or ultralow-sulfur fuels and should aim for an immediate jump to ultralow-sulfur fuels without intermediate steps. Although the premium costs imposed on low or ultralow-sulfur fuels are of concern to both policymakers and consumers, historical data has shown that the prices of low-sulfur fuels in various international oil markets have been only slightly higher than high-sulfur fuels. Moreover, the price difference between high-sulfur and low-sulfur fuels has decreased in recent years. The actual price increase associated with low-sulfur fuel is always smaller than the normal fluctuation of market fuel prices. Several countries have taken the opportunity to introduce low-sulfur fuels while fuel prices were decreasing in order to avoid perceived price increases due to fuel quality change.
In order to maximize the benefits of low and ultralow-sulfur fuels, vehicle emission standards for new and in-use vehicles should be put in place or improved – from Euro 4/Euro IV (with 50 ppm fuels) to Euro 6/VI (U.S. 2010) with 10 ppm fuels. Fine particle and black carbon emissions from diesel vehicles can be reduced by 99 percent with a transition to soot-free diesel technology. A soot-free vehicle (Euro 6/VI or U.S. 2010) – be it diesel, natural gas or electric – will emit 99% less tailpipe PM2.5 and black carbon compared to a diesel vehicle without any emission controls. Attaining these reductions requires a combination of ultralow sulfur diesel fuels (between 10-15 parts per million sulfur), tailpipe emission controls (such as Euro VI or U.S. 2010 standards), adequate compliance and enforcement systems, and inspection and maintenance practices.
Used vehicle import restrictions (including emission standards) should be combined with emission controls for vehicles. The emissions verification system may include international certified vehicle emission testing laboratories and/or Portable Emissions Measurement System (PEMS). Vehicle manufacturers and importers should be required to provide a valid “Type Approval Certificate” or “Certificate of Conformity” for both new and used vehicles entering the market. An effective in-use vehicle inspection and maintenance (I/M) program is essential to ensuring engines and emission control devices are durable and emissions are effectively controlled throughout the vehicle useful life. A centralized test-only I/M program where the inspection function is separated from the maintenance function has produced the best results. A roadside inspection program can complement periodical inspection programs for in-use vehicle but is not a replacement.