Governments and regulatory agencies in North America are evaluating the nitrogen
oxides (NOx) emissions of heavy-duty on-road vehicles to effectively
regulate these emissions in order to improve public health and meet air quality
requirements. This paper provides results from real-world Class 8
tractor-trailer truck activity and emissions data gathering conducted in the
Northeast and Mid-Atlantic United States. Unlike some other areas of the United
States (US), there is little available data on in-use operation and emissions
performance from heavy-duty trucks in this region where temperatures can be
consistently cold in winter. The purposes of this study are to add to the
literature on real-world truck operation and emissions in the Northeast and
Mid-Atlantic regions; to analyze the captured emissions data using recently
established calculation methods implemented by the California Air Resources
Board (CARB), which have not yet been applied to data from this region; and to
assist air quality regulators in identifying priorities for new heavy-duty
engine and vehicle emission standards and test procedures.
The Northeast States for Coordinated Air Use Management (NESCAUM) conducted this
project jointly with Environment and Climate Change Canada (ECCC). Given the
proximity of the truck routes evaluated in this project to the Eastern Canadian
provinces, the information is of interest to Canadian regulators as well. The
results of this data logging and analysis showed that the CARB’s three-bin
moving average window (MAW) and sum-over-sum NOx emissions
calculations can be successfully applied to in-use truck data sets. However, the
use of the on-board vehicle NOx sensors for data logging limited the
amount of time that data were able to be captured at low loads. The active
percentage time of sensors by truck was between 43% and 80% in low-load
conditions (69% over all trucks). Therefore, low-load data was “backfilled” with
estimated emissions values in order to compensate for the time the sensors were
inactive. Backfilled data showed that a range of 21% to 67% of the mass of
NOx emitted by individual trucks occurred in idle and low-load
conditions combined, whereas the original data showed values between 10% and
43%. Median daily backfilled sum-over-sum NOx emissions results by
truck specimen ranged from 0.32 g/bhp-hr to 0.75 g/bhp-hr in low-load conditions
and from 0.02 g/bhp-hr to 0.16 g/bhp-hr in high-load conditions.
As part of the study, data on over 150 vehicle and engine parameters during 100
days of truck operation were collected. This data can be used by regulators and
researchers to evaluate truck emissions and operations in the region.