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The Clean Air Diet: Knocking off the Pounds of NOx

Meeting national clean air goals for ozone requires a careful diet of emissions sources to lose the weight of dirty air. It turns out that diesel engines are one of the biggest losers.

Nitrogen Oxides (or NOx) is a ground level ozone forming compound that contributes to smog. There are no fewer than 56 sources of NOx tracked by U.S. EPA, ranging from rotting plants and soil compost to the biggest sources of emissions - mobile sources including cars, trucks, locomotives, airplanes, and equipment. Power plants (the generation of electricity) comes in second.

Top 5 Sources of NOx Emissions in 2011(2011, latest EPA data available).

Power plants and diesel engines cut about a million tons of NOx each (2008-2011); the most reductions of all 56 sectors. According to EPA, in first place for the largest reduction in NOx emissions between 2008 and 2011 is the electricity generating sector as many power plants are transitioning to newer technology. In a close second place is diesel-powered vehicles and equipment. Thanks to the transition to cleaner technology, today’s diesel engines emit a tiny fraction of emissions relative to older technology - just 1/60th the amount of emissions compared to a 1988 model. Looked at another way, you’d need 60 new tractor trailer trucks to equal the emissions of just one truck made in 1988.

Thanks to cleaner diesel fuel, advanced engines, catalysts and filters, today’s new diesel engines achieve near zero levels of emissions. And it’s not just trucks. Similar standards are now in place for off-road equipment, such as construction and agricultural equipment, beginning in 2014. 

Tons of NOx Reduced from Leading Sources 2008 - 2011

What will the future look like when more of these diesel-powered vehicles and equipment adopt clean diesel technology?

The California Air Resources Board (CARB) has been collecting information about the leading sources of NOx emissions since 1990. According to CARB data for 2012, the last year for which state-wide measured data is available, mobile sources of NOx emissions are the largest source. Unlike the rest of the country, electricity generation and other stationary sources of emissions, such as industrial activity and residential heating, make up a smaller share of emissions.

Sources of NOx Emission in California in 2012

Within the mobile source category, diesel and gasoline-powered vehicles and equipment make up much of the sources of NOx emissions. However, since 1990, diesel-related emissions have fallen significantly and are expected to continue to fall significantly in the future thanks to the adoption of new technology diesel systems in California. In fact, CARB predicts that the biggest reduction in NOx emission will come from diesel sources. 

Tons of NOx Reduced in California: 2000-2035

Commercial Trucks Delivering the NOx Reductions

Looking deeper into the NOx emissions inventory and the various diesel-powered vehicles and equipment in California, heavy-duty commercial trucks stand out as the source with one of the biggest reductions in NOx emissions. Today, California ranks towards the bottom of the list of states for the share of clean diesel commercial vehicles. Only 18 percent of California’s commercial vehicle fleet comes with an engine that meets or beats the stricter model year 2010 emissions standard. This compares to a national average of almost 26 percent while Indiana tops the list with almost 46 percent of its commercial vehicle fleet meeting or beating the model year 2010 standard.

Diesel Sources of NOx Emissions in CA

Cleaner Air, 70% Faster, with More Clean Diesel

Increasing the population of newer-generation clean diesel commercial vehicles in the California fleet will contribute to reducing NOx emissions and improving air quality. Researchers at the South Coast Air Quality Management District (SCAQMD) estimate that air quality could improve almost immediately by 70 percent if every commercial vehicle in the region met the model year 2010 standard.

How to Get 70% Reduction in NOx Emssions

The U.S. has one of the toughest emissions standards for diesel vehicles and equipment. These tough standards are coupled with strict compliance requirements to help ensure that these standards occur in practice. Thanks to decades of collaboration between manufacturers, regulators and clean air and health advocates, new technology diesel vehicles and equipment are available today and are contributing to improved air quality. Thanks to clean diesel, we can expect even greater air quality benefits in the future.



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