In-Use Emissions from 2010-Technology Heavy-Duty Trucks: Impact on Air Quality Planning in California

Introduction of a selective catalytic reduction system for heavy-duty diesel trucks (HDDTs) has substantially reduced emissions of oxides of nitrogen (NOx). However, it was found that in-use NOx emissions measured from three 2010-technology HDDTs were higher than the certification standard and higher than the levels measured during engine certification. In-use NOx emissions from three HDDTs tested over chassis dynamometer cycles were 1.7 to 9 times higher than the NOx certification standard of 0.20 grams per brake horsepower-hour, and the emissions measured with a portable emissions measurement system over highway test routes were up to five times higher than the certification standard. Such high in-use NOx emissions occurred primarily during low-speed operations (25 mph or less). This is a concern in California because more than 50% of running-exhaust NOx emissions from HDDTs will occur during low-speed operations that constitute only 11% of total vehicle miles traveled by 2025. This substantial contribution of NOx emissions during low-speed operations should be addressed carefully in the process of developing regulations and strategies to improve air quality in California. For better understanding and control of high in-use NOx emissions, there is a strong need for investigation of NOx control technologies effective at low-speed operation, differences between engine testing and whole vehicle testing procedures, and the roles of both engine certification requirements and in-use compliance requirements in reducing real-world NOx emissions.