@article{khan_frey_rastogi_wei_2020, title={Geospatial Variation of Real-World Tailpipe Emission Rates for Light-Duty Gasoline Vehicles}, volume={54}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85088496070&partnerID=MN8TOARS}, DOI={10.1021/acs.est.0c00489}, abstractNote={Spatial variability in real-world on-road tailpipe light duty gasoline vehicle nitrogen oxides, hydrocarbon, carbon monoxide, and carbon dioxide emission rates, the locations of emissions hotspots, and factors that explain spatial variability are quantified. A sample of 205 vehicles were measured on four pre-defined round trip study routes using Portable Emission Measurement Systems. The trips on each route were divided into segments, averaging ¼ mile in length. Segment-average emission rates were estimated based on measured 1 Hz emission rates. Emission hotspots are defined as segments with ≥ 90th percentile of segment-average emission rates. The hotspots have average emission rates 2 to 4 times greater, depending on the pollutant, than other segments. Hotspots are of heterogeneous characteristics including road attributes and vehicle activity metrics. For example, some hotspots were on arterial roads with an upstream signalized intersection and positive road grade, whereas some hotspots were on interstates with positive grade. Vehicle activity metrics, including average vehicle specific power and relative positive acceleration, help identify the hotspots. To reliably identify a fleet-average hotspot, data are needed for at least 36 to 130 vehicles, depending on the pollutant.}, number={14}, journal={Environmental Science and Technology}, publisher={American Chemical Society (ACS)}, author={Khan, Tanzila and Frey, H. Christopher and Rastogi, Nikhil and Wei, Tongchuan}, year={2020}, pages={8968–8979} }
 @article{khan_frey_2019, title={Effect of Air-Conditioning on Light Duty Gasoline Vehicles Fuel Economy}, volume={2673}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85063930471&partnerID=MN8TOARS}, DOI={10.1177/0361198119838507}, abstractNote={ With more stringent U.S. fuel economy (FE) standards, the effect of auxiliary devices such as air-conditioning (AC) have received increased attention. AC is the largest auxiliary engine load for light duty gasoline vehicles (LDGVs). However, there are few data regarding the effect of AC operation on FE for LDGVs based on real-world measurements, especially for recent model year vehicles. The Motor Vehicle Emission Simulator (MOVES) is a regulatory model for estimating on-road vehicle energy-use and emissions. MOVES adjusts vehicle energy-use rates for AC effects. However, MOVES-predicted FE with AC has not been evaluated based on empirical measurements. The research objectives are to quantify the LDGVs FE penalty from AC and assess the accuracy of MOVES2014a-predicted FE with AC. The AC effect on real-world fleet-average FE was quantified based on 78 AC-off vehicles versus 55 AC-on vehicles, measured with onboard instruments on defined study routes. MOVES2014a-based FE penalty from AC was evaluated based on real-world estimates and chassis dynamometer-based FE test results used for FE ratings. The real-world FE penalty ranges between 1.3% and 7.5% among a wide range of driving cycles. Fuel consumption at idle is 13% higher with AC on. MOVES underestimates the real-world FE with AC by 6%, on average. MOVES overestimates the AC effect on cycle-average FE ranging between 13.5% and 18.5% for real-world and MOVES default cycles, and between 11.1% and 14.5% for standard cycles. }, number={5}, journal={TRANSPORTATION RESEARCH RECORD}, author={Khan, Tanzila and Frey, H. Christopher}, year={2019}, month={May}, pages={131–141} }
 @article{khan_frey_2018, title={Comparison of real-world and certification emission rates for light duty gasoline vehicles}, volume={622}, ISSN={["1879-1026"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85037521775&partnerID=MN8TOARS}, DOI={10.1016/j.scitotenv.2017.10.286}, abstractNote={U.S. light duty vehicles are subject to the U.S. Environmental Protection Agency (EPA) emission standards. Emission compliance is determined by certification testing of selected emissions from representative vehicles on standard driving cycles using chassis dynamometers. Test results are also used in many emission inventories. The dynamometer based emission rates are adjusted to provide the certification levels (CL), which must be lower than the standards for compliance. Although standard driving cycles are based on specific observations of real-world driving, they are not necessarily real-world representative. A systematic comparison of the real-world emission rates of U.S. light duty gasoline vehicles (LDGVs) versus CL, and emission standards has not been previously reported. The purpose of this work is to compare regulatory limits (both CLs and emission standards) and the real-world emissions of LDGVs. The sensitivity of the comparisons to cold start emission was assessed. Portable Emission Measurement Systems (PEMS) were used to measure hot stabilized exhaust emissions of 122 LDGVs on a specified 110 mile test route. Cold start emissions were measured with PEMS for a selected vehicle sample of 32 vehicles. Emissions were measured for carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). For each vehicle, a Vehicle Specific Power (VSP) modal emission rate model was developed. The VSP modal rates were weighted by the standard driving cycles and real-world driving cycles to estimate the respective cycle average emission rates (CAERs). Measured vehicles were matched with certification test vehicles for comparison. For systematic trends in comparison, vehicles were classified into four groups based on the Tier 1 and Tier 2 emission regulation, and the vehicle type such as passenger car and passenger truck. Depending on the cycle-pollutant and the vehicle groups, hot stabilized CAERs are on average either statistically significantly higher than or significantly not different from the CLs, with the exception of CO on the US06 cycle, for which real-world rates are lower than CLs. Compared to the emission standards, hot stabilized CAERs are on average significantly lower. However, comparisons of CAERs and standards are sensitive to cold start emissions. For some combinations of pollutants and vehicle groups, cold start inclusive CAERs are higher than the corresponding CLs and as high as the standards. The CLs, which are based on standard driving cycles, tend to underestimate real-world emission rates. Therefore, emission inventory estimates using certification test results are potentially underestimated.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, publisher={Elsevier BV}, author={Khan, Tanzila and Frey, H. Christopher}, year={2018}, month={May}, pages={790–800} }
 @inproceedings{wei_christopher frey_khan_2018, title={Development and validation of transit bus energy use rate models}, volume={2018-June}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85056318902&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Wei, T. and Christopher Frey, H. and Khan, T.}, year={2018} }
 @inproceedings{khan_christopher frey_wei_2018, title={Development of updated MOVES Lite: A simplified version of MOVES}, volume={2018-June}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85056328664&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Khan, T. and Christopher Frey, H. and Wei, T.}, year={2018} }
 @inproceedings{wei_khan_frey_2017, title={Development of simplified models of CNG, diesel, and hybrid transit bus energy use}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85039153359&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Wei, T. and Khan, T. and Frey, H.C.}, year={2017} }
 @inproceedings{khan_frey_2017, title={Key factors affecting inter-county variability in moves county-level energy inventory}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85039169682&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Khan, T. and Frey, H.C.}, year={2017} }
 @article{khan_frey_2016, title={Evaluation of Light-Duty Gasoline Vehicle Rated Fuel Economy Based on In-Use Measurements}, volume={2570}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84976319253&partnerID=MN8TOARS}, DOI={10.3141/2570-03}, abstractNote={ A study demonstrated a systematic method to assess the degree of concordance between estimated real-world and the U.S. Environmental Protection Agency (EPA) rated fuel economy for light-duty gasoline vehicles based on real-world emissions measurements. Cold engine start effects are accounted for in the real-world fuel economy and in comparison with EPA ratings. Portable emissions measurement systems were used to measure emissions of carbon dioxide, carbon monoxide, hydrocarbons, and nitrogen oxides of 122 vehicles on a specified test route consisting of various roads. Fuel economy of measured vehicles was estimated considering two cases: EPA standard driving cycles and real-world driving cycles. Average cold start emissions measurements from 32 vehicles were used in sensitivity analysis of fuel economy with respect to cold start. Real-world fuel economy estimates and comparison with rated fuel economy are not highly sensitive to cold start effects. On average, both the city and highway ratings are conservative compared with real-world fuel economy. However, there are proportions of vehicles that have lower real-world fuel economy than rated. The method demonstrated should be applied to additional vehicles and real-world driving cycles. Insights from these comparisons could motivate development of a more accurate rating scheme and identification of advice to consumers to improve their fuel economy. }, number={2570}, journal={TRANSPORTATION RESEARCH RECORD}, publisher={SAGE Publications}, author={Khan, Tanzila and Frey, H. Christopher}, year={2016}, pages={21–29} }
 @inproceedings{khan_frey_2016, title={Geospatial variation of real-world emissions from a passenger car}, volume={4}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85014820615&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Khan, T. and Frey, H.C.}, year={2016}, pages={2799–2822} }
 @inproceedings{khan_frey_2015, title={Illustrative comparison between rated and real-world fuel economy and emissions}, volume={3}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84983738698&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Khan, T. and Frey, H.C.}, year={2015}, pages={1623–1641} }
 @article{wadud_khan_2013, title={Air Quality and Climate Impacts Due to CNG Conversion of Motor Vehicles in Dhaka, Bangladesh}, volume={47}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84890672548&partnerID=MN8TOARS}, DOI={10.1021/es402338b}, abstractNote={Dhaka had recently experienced rapid conversion of its motor vehicle fleet to run on compressed natural gas (CNG). This paper quantifies ex-post the air quality and climate benefits of the CNG conversion policy, including monetary valuations, through an impact pathway approach. Around 2045 (1665) avoided premature deaths in greater Dhaka (City Corporation) can be attributed to air quality improvements from the CNG conversion policy in 2010, resulting in a saving of around USD 400 million. Majority of these health benefits resulted from the conversion of high-emitting diesel vehicles. CNG conversion was clearly detrimental from climate change perspective using the changes in CO2 and CH4 only (CH4 emissions increased); however, after considering other global pollutants (especially black carbon), the climate impact was ambiguous. Uncertainty assessment using input distributions and Monte Carlo simulation along with a sensitivity analysis show that large uncertainties remain for climate impacts. For our most likely estimate, there were some climate costs, valued at USD 17.7 million, which is an order of magnitude smaller than the air quality benefits. This indicates that such policies can and should be undertaken on the grounds of improving local air pollution alone and that precautions should be taken to reduce the potentially unintended increases in GHG emissions or other unintended effects.}, number={24}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Wadud, Zia and Khan, Tanzila}, year={2013}, pages={13907–13916} }