“While this UC – Berkeley study concluded that diesel emissions were worse for smog formation than gasoline, a March 2012 study by the National Oceanographic and Atmospheric Administration (NOAA) and Cooperative Institute for Research in Environmental Science (CIRES) found that ‘gasoline emissions were the predominant contributor to the secondary organic aerosol mass’.

“Air quality and public health are important issues that we take very seriously. Atmospheric chemistry is a complex science and it is clear from this and other studies that the science is still evolving and is without a consensus. We intend to continue working with the scientific community to evaluate the science and better understand its implications.

“EPA notes that the formation of PM2.5 from NOx and VOC gases from on-road mobile sources is not a constant value or conversion factor. Many environmental factors are responsible for the conditions that make it favorable or unfavorable for formation of PM2.5 from these compounds.  

“While the scientific debate will continue on atmospheric chemistry, there is no debate about the impact of clean diesel technology in terms of air quality and emissions of fine particles. No other sector has done more to improve California’s air quality in the last decade than diesel. 

"According to the California Air Resources Board (ARB), particulate emissions from heavy-duty diesel trucks have declined from 7.5 percent of the overall state inventory in 1990 to 3.8 percent in 2008, and by 2020 it will be just 1.6 percent. The ARB also projects that from 2008 to 2020, while emissions of all sources of PM are expected to increase by 3.2 percent, PM from all diesels will decline by 58 percent.

“These unprecedented reductions in emissions levels are a direct result of the billions of dollars of investments in cleaner fuels and advanced diesel engines and emissions controls to meet the challenges established by the ARB and the EPA.


"Today, clean diesel technology enables new commercial trucks, construction machines and farm equipment to achieve near zero emissions.

“According to the EPA, nationwide fine particles from diesel engines now make up less than six percent of the entire particulate emission inventory. Today in California, more fine particles come from brake dust and tire wear than from diesel emissions."  FG 

—From Diesel Technology Forum news release