Effects of Ambient Temperature on NOx Emissions from Heavy-Duty Diesel Vehicles Measured in Utah
Abstract
1. Introduction
2. Materials and Methods
- NOx = estimated NOx emissions in g/kg-fuel,
- a = baseline emissions at age 0 (years) and temperature 0 (°C),
- b = the temperature coefficient (°C),
- c = the age coefficient (years),
3. Results
4. Discussion
Study | Summary | Temperature Range | Study NOx Temperature Effect | Equation (2) Temperature Effect 2 |
---|---|---|---|---|
Evans et al., 2019 [23] | Measured near-road NOx concentrations at three ranges of ambient temperature. Observed significantly higher NOx during colder temperatures. | −15 °C to 15 °C | ~1.8 1 | 1.9 |
Grange et al., 2019 [24] | On-road remote sensing of LD diesel vehicles across the UK from 2017 to 2018. Higher NOx at colder ambient temperatures. | 0 °C to 25 °C | 2.0 | 1.7 |
Hall et al., 2020 [22] | Used near-road and aircraft observations to observe CO, NOx and CO2. Found that NOx emissions increase at colder temperatures. | −5 °C to 25 °C | 2.0 | 1.9 |
Söderena et al., 2020 [41] | Measured tailpipe emissions from one car equipped with SCR during 2018 and 2019. No significant difference in emissions across temperature range for the vehicle. | 7 °C to 17 °C | No significant observed effect | 1.2 |
US EPA, 2023 [21] | EPA’s MOVES model temperature adjustment for HD NOx starting in model year 2027. Adjustment is based on in-lab testing of a prototype model year 2027 engine at cold ambient temperatures in 2022. Found variation in temperature effect by regulatory class. | −4.4 °C to 25 °C | 1.2 to 1.3 | 1.8 |
Wang et al., 2019 [8] | Measured vehicle emissions at Fort McHenry Tunnel in Baltimore, MD, in 2015. HD vehicles were estimated separately from LD and had higher emissions at colder temperatures. | 7.1 °C to 29.7 °C | 1.7 | 1.6 |
Wærsted et al., 2022 [42] | Measured road traffic NOx emissions for 4 years at 46 sites from 2016 to 2019 in Norway. Observed higher NOx emissions at colder temperatures. | −7 °C to 14 °C | 2.7 | 1.6 |
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
NOx | Nitrogen oxides |
FEAT | Fuel Efficiency Automobile Test |
HD | Heavy-duty |
SCR | Selective catalytic reduction |
CO | Carbon monoxide |
HC | Hydrocarbons |
NH3 | Ammonia |
LD | Light-duty |
Appendix A
Appendix A.1
Appendix A.2
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Campaign | Winter 2020 | Summer 2023 |
---|---|---|
Location | Perry, UT | Perry, UT |
Dates | 12/10/20–12/11/20 | 7/31/23–8/01/23 |
Daily Average Temperature (°C/°F) | −4.4, 24 | 28.1, 82.5 |
Daily Average Humidity (%) | 61.3 | 29.4 |
Location Elevation (Meters/Feet) | 1131, 4301 | 1131, 4301 |
Number of Vehicles Matched to Records | 549 | 527 |
Average Vehicle Acceleration (mph/s) | 0.03 | 0.45 |
Average Vehicle Speed (mph) | 26.4 | 28.6 |
Location Slope (degrees) | 0° | 0° |
Median Vehicle Age (Years) | 2 | 2 |
Median Chassis Model Year | 2018 | 2021 |
Mean gNOx/kg-fuel (95% CI) | 9.1 (7.8–10.4) | 5.7 (4.2–7.1) |
Mean gNO 1/kg-fuel (95% CI) | 8.6 (7.4–9.8) | 5.0 (3.7–6.2) |
Mean gNO2/kg-fuel (95% CI) | 0.5 (0.4–0.6) | 0.7 (0.4–1.0) |
Chassis Model Year | Winter 2020 | Summer 2023 | ||
---|---|---|---|---|
Age | n | Age | n | |
2024 | - | - | 0 | 38 |
2023 | - | - | 0 | 118 |
2022 | - | - | 1 | 91 |
2021 | 0 | 50 | 2 | 60 |
2020 | 0 | 93 | 3 | 62 |
2019 | 1 | 112 | 4 | 43 |
2018 | 2 | 82 | 5 | 37 |
2017 | 3 | 45 | 6 | 17 |
2016 | 4 | 60 | 7 | 31 |
2015 | 5 | 54 | 8 | 11 |
2014 | 6 | 24 | 9 | 11 |
2013 | 7 | 16 | 10 | 2 |
2012 | 8 | 10 | 11 | 4 |
2011 | 9 | 3 | 12 | 2 |
Winter 2020 | Summer 2023 | Ratio of Sample Means (Winter/Summer) | Ratio of GAM Means (Winter/Summer) | |||
---|---|---|---|---|---|---|
Age | Sample Means | GAM Means | Sample Means | GAM Means | ||
0 | 4.6 | 4.7 | 1.1 | 1.0 | 4.2 | 4.5 |
1 | 6.0 | 5.9 | 1.3 | 1.7 | 4.5 | 3.4 |
2 | 5.4 | 5.5 | 3.5 | 2.5 | 1.6 | 2.2 |
3 | 6.0 | 6.7 | 2.1 | 3.0 | 2.9 | 2.2 |
4 | 11.6 | 11.2 | 8.5 | 8.1 | 1.4 | 1.4 |
5 | 14.7 | 14.3 | 12.4 | 11.1 | 1.2 | 1.3 |
6 | 16.2 | 16.9 | 3.0 | 6.9 | 5.5 | 2.5 |
7 | 25.2 | 25.4 | 14.4 | 13.3 | 1.7 | 1.9 |
8 | 39.9 | 43.4 | 28.6 | 31.6 | 1.4 | 1.4 |
9 | 80.4 | 70.4 | 44.8 | 39.9 | 1.8 | 1.8 |
10 | - | - | 12.4 | 39.1 | - | - |
11 | - | - | 45.1 | 35.3 | - | - |
12 | - | - | 14.0 | 21.5 | - | - |
Term | Parameter | Estimate | 95% Confidence Intervals (Lower, Upper) | p-Value |
---|---|---|---|---|
a | Intercept (gNOx/kg-fuel) | 3.417 | (2.706, 4.231) | <2 × 10−16 |
b | Temperature (°C) | −0.021 | (−0.027, −0.015) | <3 × 10−12 |
c | Age (Years) | 0.287 | (0.259, 0.321) | <2 × 10−16 |
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Gurecki Allen, A.L.; Sonntag, D.B.; Bishop, G.A. Effects of Ambient Temperature on NOx Emissions from Heavy-Duty Diesel Vehicles Measured in Utah. Environments 2025, 12, 293. https://doi.org/10.3390/environments12090293
Gurecki Allen AL, Sonntag DB, Bishop GA. Effects of Ambient Temperature on NOx Emissions from Heavy-Duty Diesel Vehicles Measured in Utah. Environments. 2025; 12(9):293. https://doi.org/10.3390/environments12090293
Chicago/Turabian StyleGurecki Allen, Amber L., Darrell B. Sonntag, and Gary A. Bishop. 2025. "Effects of Ambient Temperature on NOx Emissions from Heavy-Duty Diesel Vehicles Measured in Utah" Environments 12, no. 9: 293. https://doi.org/10.3390/environments12090293
APA StyleGurecki Allen, A. L., Sonntag, D. B., & Bishop, G. A. (2025). Effects of Ambient Temperature on NOx Emissions from Heavy-Duty Diesel Vehicles Measured in Utah. Environments, 12(9), 293. https://doi.org/10.3390/environments12090293