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Air quality impacts of motor vehicle emissions in the south coast air basin: Current versus more stringent control scenario
Atmospheric Environment 47 (2012) 236e240
Contents lists available at SciVerse ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
Air quality impacts of motor vehicle emissions in the south coast air basin: Current versus more stringent control scenario Susan Collet a, *, Toru Kidokoro b, Yukihiro Sonoda b, Kristen Lohman c,1, Prakash Karamchandani c,1, Shu-Yun Chen c,1, Hiroaki Minoura d a
Toyota Motor Engineering and Manufacturing North America, Inc, Ann Arbor, MI 48105, United States Toyota Motor Corporation, Susono, Shizuoka, 410-1193, Japan Atmospheric and Environmental Research, Inc., San Ramon, CA 94583, United States d Toyota Central R&D Labs., Inc, Nagakute, Aich 480-1192, Japan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 June 2011 Received in revised form 28 October 2011 Accepted 3 November 2011
States are working to comply with the ozone National Ambient Air Quality Standards (NAAQS). Often, regulations restricting vehicle emissions are promulgated in order to attain compliance with the NAAQS. Currently, more stringent vehicle emission regulations are being considered by government agencies. This paper compares emissions from passenger cars and light duty trucks under the current California Low Emission Vehicle (LEV II) standards to a control scenario which was anticipated in 2008 to become LEV III (referred to as “more stringent control” in this paper) and determines if the scenario would result in additional improvements to air quality in California’s South Coast Air Basin. The air quality modeling was performed using the Community Multi-scale Air Quality Model (CMAQ) for years 2005, 2014 and 2020. The more stringent control sensitivity study simulated a scenario in which all new passenger cars and light duty trucks in the California South Coast Air Basin in year 2016 achieve Super Ultra-Low Emission Vehicle (SULEV) tail pipe emissions, zero evaporative emissions and more stringent aggressive driving requirements. The total on-road vehicles emissions difference when averaged across the South Coast Air Basin showed the more stringent scenario compared to LEV II to have reductions of 1% for oxides of nitrogen (NOx), 1% for as reactive organic gases (ROG) and 5% for carbon monoxide (CO) in 2030. LEV II modeled ozone levels in the western areas of the basin increased in 2014 and 2020 as compared to 2005, because these areas are VOC-sensitive and the reductions in NOx emissions in these regions are larger than the VOC reductions. In other areas of the South Coast Basin, ozone is reduced by 1.5% or less. The more stringent control scenario modeled levels of ozone have a maximum decrease from LEV II levels by 1% or less in 2014 and 1.5% or less in 2020. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Air quality Motor vehicle emissions South coast air basin NAAQS Ozone ROG CO NOx CMAQ LEV II LEV III SULEV Zero evap 2005 2014 2020
1. Introduction State programs to attain ozone National Ambient Air Quality Standards (NAAQS) have a direct impact on motor vehicles because their hydrocarbon and nitrogen oxide emissions contribute to the formation of ozone in the atmosphere. Vehicle emissions are highly regulated and more stringent regulations are being considered by government agencies for the criteria pollutants hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and particulate matter (PM) (“Emission standards for new motor vehicles or new motor vehicle engines,” Title II, Code of Federal Regulations, Part A, * Corresponding author. Tel.: þ1 7349952086. E-mail address: [email protected] (S. Collet). 1 Currently at ENVIRON International Corporation, Navato, CA 94945, United States. 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.11.010
Section 202). NOx and Volatile Organic Compounds (VOCs) emitted from anthropogenic and biogenic sources are the two main precursors that lead to ground level ozone formation (Seinfeld and Pandis, 1998). For those mobile source related criteria pollutants, the United States Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have established standards and test procedures for exhaust and vapor emissions. The exhaust measurements are determined during driving a pattern referred to as the federal test procedure (FTP) and from driving a pattern referred to as supplemental federal test procedure (SFTP) which is driving under high speed/high load conditions and driving while operating air conditioning. The vapor emissions are from vapors escaping from the vehicle (evaporative emissions) and refueling emissions. The current program in California is the second low emission vehicle program (LEV II).
S. Collet et al. / Atmospheric Environment 47 (2012) 236e240
2. Methodology This paper focuses on determining if a scenario anticipated in 2008 to become the next level of low emission vehicle (LEV III) requirements, referred in this paper as “more stringent control scenario,” would result in additional improvements to air quality in the South Coast Air Basin (SoCAB) compared to the existing LEV II requirements. Emissions inventory and air quality modeling were performed for calendar years 2005, 2014 and 2020 for the California South Coast Air Basin (SoCAB). The vehicle emission controls studied were regarding the standards expected to change, which were FTP, evaporative and SFTP emissions. The simulation was applied to three categories: passenger cars, light-duty trucks between 0 and 3750 pounds loaded vehicle weight (LDT1) and light-duty trucks between 3751 and 5750 pounds loaded vehicle weight (LDT2). The total on-road fleet includes light, medium and heavy duty vehicles and motorcycles. The base scenario used the current California low emission vehicle (LEV II) standard. The more stringent control scenario modified the emissions inventory where all new passenger cars and light duty trucks in the SoCAB in year 2016 achieved Super Ultra-Low Emission Vehicle (SULEV) tail pipe emissions, zero evaporative emissions and more stringent aggressive driving requirements. An analysis estimated regional emissions of Non-Methane Organic Gases (NMOG) modeled as reactive organic gases (ROG), NOx, and CO. Then, the effect on ozone concentrations in the SoCAB was assessed using an existing air quality model and South Coast Air Management District input files. 2.1. Emissions inventory and modeling The emission inventory modeling tool used for this study was CARB’s Emission Factors (EMFAC2007) model (CARB, 2006) to study LEV II and the more stringent control scenario FTP, evaporative and SFTP vehicle emissions. EMFAC2007 combined detailed information on California’s fleet of motor vehicles, roadway information, vehicle miles traveled and detailed emission factors to estimate the emission rates of important air pollutants. EMFAC can be used to calculate emissions for the state, county, air basin, or air pollution control district. For this study, emissions for the South Coast Air Quality Basin (SoCAB) were calculated. The SoCAB encompassed all of Orange County and the majority of Los Angeles County, as well as the urban portions of Riverside and San Bernardino Counties. EMFAC was designed with a “Default” setting which reflects the current projections and estimates for each model year from 1970 to 2040. Emission inventories for the years 2006 through 2030 were calculated. The percentage of the new light duty fleet meeting revised emission restrictions was increased and the other vehicle technology percentages were reduced, thus the number of vehicles in the fleet overall did not change. The base case EMFAC default vehicle fleet settings were modified to reflect the anticipated more stringent scenario phase-in percentages and emission requirements for FTP, evaporative and SFTP. The anticipated requirement for FTP emissions increased the amount of SULEV vehicles. The percentage of new vehicles meeting the SULEV standard in 2013, 2014, 2015 and 2016 were 59, 72, 86 and 100 respectively. Currently, most vehicles achieve the near-zero evaporation or partial zero evaporation categories. The per-test evaporative standards were translated into emissions per vehicle or per start emission factors and were used to calculate total evaporative emissions for a population of near-zero evaporative emissions vehicles in EMFAC2007. A small fraction of vehicles, such as electric vehicles, belong to the zero evaporation category. Zero evaporation vehicles are not associated with any fuel-related evaporation, but are associated with evaporation from non-fuel components, such as wind shield wiper fluid, paint, etc. In EMFAC2007, the definition of zero emission
237
vehicles (ZEV) included only non-fuel related evaporation. Therefore, this vehicle type was used to model a vehicle with zero fuel-related evaporative emissions regardless of fuel type. However, EMFAC allows only passenger car and LDT1 vehicles to be modeled as ZEV vehicles. The LDT2 vehicles were maintained at default technologies. The more stringent scenario modeled new vehicles to have zero evaporative emissions in 2013, 2014, 2015 and 2016 with 25%, 50%, 75% and 100% respectively. Table 1 outlines the total light duty fleet by SULEV and zero evaporative technology for LEV II and more stringent scenario. Supplemental Federal Test Procedure (SFTP) standards are not explicitly modeled in the EMFAC2007 software. So, these testbased standards were translated to an emission inventory. SFTP conditions include the use of driving high speed/high load and using the air conditioning. The current SFTP standard in LEV II applies to new vehicles (4000 miles), while the more stringent control scenario SFTP (SFTP-2) was applied to in-use vehicles (150,000 miles). Next, the federal SFTP weighting scheme for the amount of time or miles corresponding to the driving conditions was determined to be appropriate. This was because California and Federal compliance for SFTP was intended to be harmonized. To calculate the effects of SFTP-2, the LEV II SFTP emission inventory was generated using EMFAC2007 for years 2006e2030. The vehicle emission technology mix for LEV, ULEV and SULEV was fixed for 2008 and beyond. For each vehicle emission technology, a ratio was derived based on the SFTP to SFTP-2 standard. The ratio was applied to vehicles for each technology group in 2012, 2013, 2014 and 2015 as 25%, 50%, 75% and 100% respectively. Using EMFAC2007 the emission inventory of LEV II and the more stringent scenario was determined and compared for total emissions, and then was used to separately analyze evaporative and SFTP requirements results. Table 2 shows the emission inventory modeling results for LEV II and the more stringent scenario total in the year the revised standards would have been completely phased-in, 2016, and in a year to represent long term results, 2030. For developing percentage comparisons, emission results were compared to their 2006 emissions. Total ROG, CO, and NOx emissions included exhaust and evaporative emissions for all on-road vehicles. Since exhaust emissions from light duty vehicles represent a fraction of total on-road emissions, the difference comparing LEV II to the more stringent control scenario for ROG, CO, and NOx emissions in 2030 were from zero (0) to five (5) percent. Changes to both evaporative and SFTP standards had nearly zero difference between the standards until 2016 because of the limited phased-in percentage. Evaporative emission standards only affect ROG emissions. So, by 2030, there was a 2% reduction in ROG when comparing near-zero evaporative emissions and the more stringent control scenario zero emission standard. Regarding the SFTP portion of the emission inventory study, in 2030 the difference between SFTP and SFTP-2 for NOx and ROG combined emissions had 1% reduction, while CO had 4% reduction.
2.2. Air quality modeling Air quality modeling was conducted for the SoCAB using existing models and input data sets. The U.S. EPA Community Multiscale Air Quality (CMAQ Version 4.6, released in October 2006) model (Byun and Schere, 2006; http://www.cmaq-model.org/) was used. Table 1 South Coast Air Basin light duty vehicle fleet percentage by technology for the LEV II and more stringent scenarios. 2006
2016
2020
2030
SULEV
LEV II More Stringent
5% 5%
15% 26%
20% 45%
24% 78%
Evaporative zero
LEV II More Stringent
1%e2% 1%e2%
1%e2% 12%
1%e2% 26%
1%e2% 53%
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S. Collet et al. / Atmospheric Environment 47 (2012) 236e240
Table 2 On-road mobile source emission inventory comparison between LEV II and the more stringent scenario. 2006
2016
2030
Base
Difference from base (%)
Difference from base (%)
LEV II
More stringent
More stringent compared to LEV II
LEV II
More stringent
More stringent compared LEV II
Total mobile source
ROG CO NOx
261 2614 549
51% 45% 49%
51% 43% 48%
0% 2% 1%
33% 26% 26%
32% 21% 25%
1% 5% 1%
Evaporative
ROG
261
51%
51%
0%
32%
30%
2%
SFTP
ROG þ NOx CO
810 2614
51% 50%
50% 50%
1% 0%
29% 28%
28% 24%
1% 4%
The CMAQ model configuration selected used the SAPRC-99 chemical mechanism (Carter, 2000) for the gas-phase chemistry, the Asymmetric Convective Model Version 2 for the vertical diffusion and global mass-conserving schemes to calculate horizontal and vertical advection. The photolysis rate look-up tables for this episode were created from the Total Ozone Mapping Spectrometer (TOMS) (ftp://toms.gsfc.nasa.gov/pub/eptoms/data/ozone/Y2005) ozone column data and used the CMAQ photolysis rate processor (JPROC). Air quality modeling input data sets were based on South Coast Air Quality Management District (SCAQMD) data sets used for their 2007 Air Quality Management Plan (AQMP) (SCAQMD, 2007). SCAQMD provided emission data for years 2005, 2014, and 2020. The data were available as gridded data and further divided by county and air basin. The domain was defined in a Lambert Conformal Conic Projection and consisted of 116 80 grid cells in the horizontal with a grid resolution of 5 km. The domain, shown in Fig. 1, covered 232,000 square kilometers (over 89,000 square miles). The northern boundary of the domain extended into Santa Barbara and Kern counties, while the southern boundary extended into Mexico. The eastern boundary of the domain was in the desert portions of San Bernardino and Riverside counties, while the western boundary extended approximately 200 km from the coastline in Los Angeles County. SCAQMD provided July 2005 initial and boundary condition output files, and the meteorological episode output files from the Mesoscale Model, MM5. The CMAQ ready meteorological files were prepared using the MeteorologyChemistry Interface Processor (MCIP), Version 3.3. The 34-layer MM5 output files were mapped into 17 CMAQ layers. The SCAQMD set of emission inventory files included area, biogenics, mobile, point and Mexico sources as well as stack parameter files, temporal allocation tables and speciation profiles. To prepare the
files for use in the CMAQ simulation, a method was developed to process inventory files, match the stack information and temporal profiles, speciate the pollutants to the SAPRC-99 chemical mechanism species, and finally generate three-dimensional NetCDF files. The different inventory categories were processed separately and later merged together to a single gridded file. The emissions were summed over all source categories and also summed over all model layers. To establish a reference point for the emission scenario simulations, to verify model performance, and to gain confidence in model predictions, the CMAQ model was used for a SoCAB episode in July 2005 when high concentrations of ozone were observed. The five-day episode used in the modeling was from July 14 through July 19, 2005 using modeling inputs from SCAQMD. The episode had typical southern California climate conducive to high air pollution episodes, i.e., stagnant flow, strong subsidence induced by synoptic scale high pressure, and subsequently limited vertical mixing and spatial dispersion (Lee et al., 2009). On July 15 the peak 8-hour ozone concentration of 143 ppb was observed while the model predicted 106 ppb. Thus, the model underpredicted the peak observed 8-hour ozone concentration on July 15 by about 25%. The model performance evaluation statistics are listed in Table S1. The model tends to underpredict ozone concentrations, with a normalized bias of 22%. This bias is higher than the EPA-recommended normalized bias of 15%. The normalized gross error is 30%, and is within the EPA-recommended goal of 35%. This tendency to underpredict peak 8-hour ozone concentrations is consistent with results from the SCAQMD application of Comprehensive Air Quality Model with Extensions (CAMx) for the 2007 AQMP (SCAQMD, 2007). As noted by Lee et al. (2009), the model performance was related to deficiencies in the meso-scale model (known as MM5) meteorological fields. Lee et al. (2009) made some modifications to the MM5 fields and found that these modifications resulted in improved air quality model predictions of ozone and CO concentrations for the SoCAB. Since results of this modeling were similar to the SCAQMD results, using these models, data and processes provided a scientifically credible approach for assessing future emission inventory changes on air quality. 3. Results, air quality
Fig. 1. Modeling domain for CMAQ simulations.
The potential impact of vehicle emissions on ozone concentrations in the SoCAB was predicted for years 2005, 2014 and 2020 using the LEV II emissions inventory in the CMAQ model. The first step was to predict the base year, 2005. Then the 2005 LEV II emission inventory was replaced with 2014 LEV II and then 2020 LEV II emission inventories. Next, the 2014 and 2020 LEV II emission inventories were revised with the more stringent control scenario emission inventories. Only varying the light duty vehicle emission inventory kept the model performance statistics constant
S. Collet et al. / Atmospheric Environment 47 (2012) 236e240
239
and isolated the effect of changing light duty vehicle emissions. The predicted 8-hour average ozone concentrations for July 15, 2005 LEV II emissions are shown in Fig. 2a. Fig. 2b shows the predicted 8-h average ozone concentrations using 2005 meteorology and replacing the emissions inventory with 2014 emissions inventory. Fig. 3a shows the percent change in predicted 8-hour ozone concentrations between 2005 and 2014. Fig. 3b represents the percent change in predicted 8-h ozone concentrations between 2005 and 2020. The spatial distribution of CO, NOx and ROG emissions resulted in reducing emissions in 2014 and 2020 when compared to 2005. Ozone concentrations decrease up to 28% over large areas of the basin. However, since the western portions of the basin NOx emission reductions were larger than the reductions in ROG emissions, as shown in Table 2, and because the western portion of the basin is VOC- sensitive, the predicted ozone concentration for this region would increase 30% or more in both 2014 and 2020 compared to 2005. Next, replacing LEV II emission inventory with the more stringent control emission inventory predicted ozone concentrations to change between 1% to 0.8%, in 2014 and 2020 as shown in Figs. 4 and 5 respectively. Next, changes to ozone concentration due to changing separately the evaporative emission and SFTP-2 standards were explored. As previously described, evaporative emission standards do not affect NOx emissions. In 2014, changing only the evaporative portion of the LEV II to the more stringent control scenario’s emission inventories resulted in negligible ROG emission reduction
Fig. 3. a: Relative change in predicted 8-h average surface O3 concentrations when 2005 emissions (Fig. 2a) are replaced by 2014 LEV II emissions (Fig. 2b). b: Relative change in predicted 8-h average surface O3 concentrations when 2005 emissions (Fig. 2a) were replaced by 2020 LEV II based emissions. Predicted ozone concentrations change from by increasing in the green, yellow and red areas and decreasing in the blue areas.
and, subsequently, negligible ozone concentration change. In 2020 compared to 2014 the more stringent control evaporative scenario resulted in up to 2% decrease in ROG emissions, and subsequently, decreased 8-hour average ozone concentrations less than 0.2%. Compared to the LEV II SFTP emissions for 2014 and 2020, SFTP-2 resulted in reducing ROG plus NOx and CO emissions. Because ozone formation in the South Coast Air Basin, particularly in the western and central portions of the basin, is VOC-sensitive with respect to ozone formation, the 8-h average ozone concentrations in the western portion of the basin increased up to 2% and in other areas decreased up to 1% in 2014 and 2020 respectively.
4. Summary and discussion
Fig. 2. a. Predicted 8-h average surface O3 concentrations on July 15, 2005. b. Predicted 8-h average surface O3 concentrations on July 15, 2005 using 2014 LEV II emission inventory.
This paper compared emissions from passenger cars and light duty trucks under the current California Low Emission Vehicle (LEV II) standards to a control scenario which was anticipated in 2008 to become LEV III (referred to as “more stringent control” in this paper) and determined if the scenario would result in additional improvements to air quality in California’s South Coast Air Basin. The air quality modeling was done using the Community Multi-scale Air Quality Model (CMAQ) for years 2005, 2014 and 2020 and emission inventories supplied by SCAQMD. The study was applied to passenger cars and light duty trucks in the South Coast
240
S. Collet et al. / Atmospheric Environment 47 (2012) 236e240
Fig. 4. Relative change in predicted 8-h average surface O3 concentrations when the 2014 LEV II emission inventory results were replaced with the 2014 more stringent case scenario. Predicted ozone concentrations change in 2014 between LEV II and the more stringent scenario by increasing in the green areas and decreasing in the blue areas.
Air Basin. Emission inventories and ozone concentrations were studied for the current California LEV II standards and a more stringent control scenario. The existing standards and the more stringent control scenario had nearly identical emission inventory and ozone concentration results. The resulting emission reductions for on-road vehicles averaged across the South Coast Air Basin showed the more stringent scenario compared to the current California Low Emission Vehicle (LEV II) regulations would have 1% for NOx, 1% for ROG and 5% for CO reduction in 2030. Relative to 2005, in 2014 and 2020 the LEV II and more stringent control scenario show ozone concentrations decrease over large areas of the basin. However, ozone levels in the western portions of the basin increase because these areas are VOC-sensitive and the reductions in NOx emissions are larger than VOC reductions. Projected ozone increases in some areas and decreases in other areas are a result of emission changes, meteorology and photochemistry. When VOC levels are high relative to NOx, in areas with large biogenic VOC emissions, ozone is reduced by NOx reductions and increased by NOx increases. Such conditions are called “NOx -limited” or “NOx -sensitive.” Predicted ozone reductions in the non-western SoCAB area are likely achieved by
reducing NOx. However, when NOx levels are relatively high and VOC levels are relatively low, increases in NOx can decrease ozone, because NO reacts directly with ozone and NO2 terminates radicals, forming nitric acid, which is removed from the system or forms particulate nitrates. Such conditions are called “VOC-limited,” “VOC-sensitive” or “NOx -saturated.” Under these conditions, VOC reductions are effective in reducing ozone, but NOx reductions can increase ozone under certain circumstances. Hence, decreasing NOx more than decreasing VOC results in ozone increases (Cook et al., 2010). The ozone increase predicted in the western portion of the SoCAB is because the area is likely VOC-sensitive and is projected to experience NOx decreases. Separate analysis of emission changes due to revising the evaporative and SFTP standards was performed. The evaporative standard comparison projected the more stringent control scenario versus LEV II for 2020 would have additional reductions of about 2% in ROG emissions compared to the current standard; subsequently this produced less than 0.2% reduced ozone concentrations. The current SFTP and more stringent control scenario SFTP-2 would potentially reduce emissions for CO, NOx and ROG for on-road vehicles across the SoCAB. Again, the NOx emissions are reduced more than the VOC emissions. So, the scenario resulted in up to 1.7% increased ozone concentration in the VOC-sensitive western portion of the Basin, and decreased up to 1% in NOx-sensitive areas. The current LEV II and future more stringent control scenario requirements will achieve emission reductions in the SoCAB; however, the results may not have a desired affect on ozone in the entire SoCAB. There are limitations and uncertainties in determining emission inventories, performing emission inventory modeling and air quality modeling. This study provided a relative comparison of current versus future standards without changing other variables. Acknowledgements The work reported herein was performed by Atmospheric and Environmental Research, Inc. (AER) under a contract from Toyota Motor Engineering and Manufacturing North America, Inc. (TEMA). While the work was performed by AER, the conclusions are those of the authors and do not necessarily reflect the views of AER. Appendix. Supplementary data Supplementary data associated with this article can be found in the online version, at doi:10.1016/j.atmosenv.2011.11.010. References
Fig. 5. Relative change in predicted 8-h average surface O3 concentrations when the 2020 LEV II emission inventory results were replaced with the 2020 more stringent case scenario. Predicted ozone concentrations change in 2020 between LEV II and the more stringent scenario by increasing in the green areas and decreasing in the blue areas.
Byun, D., Schere, K.L., 2006. Review of governing equations, computational algorithms, and other components of the Models-3 Community Multiscale Air Quality (CMAQ) modeling system. Appl. Mech. Rev. 59, 51e77. http://www. cmag-model.org. Carter, W.P.L., 2000. SAPRC-99 Mechanism files and associated programs and examples. Available at: http://www.engr.ucr.edu/wcarter/SAPRC99/index.htm. CARB http://www.arb.ca.gov/msei/onroad/doctable_test.htm Public meeting to consider approval of revisions to the state’s on-road motor vehicle emissions inventory, technical support document, May 2000. CARB, November 2006. EMFAC2007 User’s Guide. http://www.arb.ca.gov/msei/ onroad/downloads/docs/user_guide_emfac2007.pdf. Cook, R., et al., 2010. Air quality impacts of increased use of ethanol under the United States’ Energy Independence and Security Act. Atmos. Environ 45, 7714e7724. Lee, S.M., Princevac, M., Mitsutomi, S., Cassmassi, J., 2009. MM5 simulations for air quality modeling: an application to a coastal area with complex terrain. Atmos. Environ. 43, 447e457. SCAQMD, 2007. Final 2007 air quality management plan, South Coast Air Quality Management District, Diamond Bar, CA. Available from: http://www.aqmd.gov/ aqmp/07aqmp/aqmp/Complete_Document.pdf. Seinfeld, J.H., Pandis, S.N., 1998. Atmospheric Chemistry and Physics. John Wiley & Sons, New York.
Contents lists available at SciVerse ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
Air quality impacts of motor vehicle emissions in the south coast air basin: Current versus more stringent control scenario Susan Collet a, *, Toru Kidokoro b, Yukihiro Sonoda b, Kristen Lohman c,1, Prakash Karamchandani c,1, Shu-Yun Chen c,1, Hiroaki Minoura d a
Toyota Motor Engineering and Manufacturing North America, Inc, Ann Arbor, MI 48105, United States Toyota Motor Corporation, Susono, Shizuoka, 410-1193, Japan Atmospheric and Environmental Research, Inc., San Ramon, CA 94583, United States d Toyota Central R&D Labs., Inc, Nagakute, Aich 480-1192, Japan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 June 2011 Received in revised form 28 October 2011 Accepted 3 November 2011
States are working to comply with the ozone National Ambient Air Quality Standards (NAAQS). Often, regulations restricting vehicle emissions are promulgated in order to attain compliance with the NAAQS. Currently, more stringent vehicle emission regulations are being considered by government agencies. This paper compares emissions from passenger cars and light duty trucks under the current California Low Emission Vehicle (LEV II) standards to a control scenario which was anticipated in 2008 to become LEV III (referred to as “more stringent control” in this paper) and determines if the scenario would result in additional improvements to air quality in California’s South Coast Air Basin. The air quality modeling was performed using the Community Multi-scale Air Quality Model (CMAQ) for years 2005, 2014 and 2020. The more stringent control sensitivity study simulated a scenario in which all new passenger cars and light duty trucks in the California South Coast Air Basin in year 2016 achieve Super Ultra-Low Emission Vehicle (SULEV) tail pipe emissions, zero evaporative emissions and more stringent aggressive driving requirements. The total on-road vehicles emissions difference when averaged across the South Coast Air Basin showed the more stringent scenario compared to LEV II to have reductions of 1% for oxides of nitrogen (NOx), 1% for as reactive organic gases (ROG) and 5% for carbon monoxide (CO) in 2030. LEV II modeled ozone levels in the western areas of the basin increased in 2014 and 2020 as compared to 2005, because these areas are VOC-sensitive and the reductions in NOx emissions in these regions are larger than the VOC reductions. In other areas of the South Coast Basin, ozone is reduced by 1.5% or less. The more stringent control scenario modeled levels of ozone have a maximum decrease from LEV II levels by 1% or less in 2014 and 1.5% or less in 2020. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Air quality Motor vehicle emissions South coast air basin NAAQS Ozone ROG CO NOx CMAQ LEV II LEV III SULEV Zero evap 2005 2014 2020
1. Introduction State programs to attain ozone National Ambient Air Quality Standards (NAAQS) have a direct impact on motor vehicles because their hydrocarbon and nitrogen oxide emissions contribute to the formation of ozone in the atmosphere. Vehicle emissions are highly regulated and more stringent regulations are being considered by government agencies for the criteria pollutants hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and particulate matter (PM) (“Emission standards for new motor vehicles or new motor vehicle engines,” Title II, Code of Federal Regulations, Part A, * Corresponding author. Tel.: þ1 7349952086. E-mail address: [email protected] (S. Collet). 1 Currently at ENVIRON International Corporation, Navato, CA 94945, United States. 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.11.010
Section 202). NOx and Volatile Organic Compounds (VOCs) emitted from anthropogenic and biogenic sources are the two main precursors that lead to ground level ozone formation (Seinfeld and Pandis, 1998). For those mobile source related criteria pollutants, the United States Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have established standards and test procedures for exhaust and vapor emissions. The exhaust measurements are determined during driving a pattern referred to as the federal test procedure (FTP) and from driving a pattern referred to as supplemental federal test procedure (SFTP) which is driving under high speed/high load conditions and driving while operating air conditioning. The vapor emissions are from vapors escaping from the vehicle (evaporative emissions) and refueling emissions. The current program in California is the second low emission vehicle program (LEV II).
S. Collet et al. / Atmospheric Environment 47 (2012) 236e240
2. Methodology This paper focuses on determining if a scenario anticipated in 2008 to become the next level of low emission vehicle (LEV III) requirements, referred in this paper as “more stringent control scenario,” would result in additional improvements to air quality in the South Coast Air Basin (SoCAB) compared to the existing LEV II requirements. Emissions inventory and air quality modeling were performed for calendar years 2005, 2014 and 2020 for the California South Coast Air Basin (SoCAB). The vehicle emission controls studied were regarding the standards expected to change, which were FTP, evaporative and SFTP emissions. The simulation was applied to three categories: passenger cars, light-duty trucks between 0 and 3750 pounds loaded vehicle weight (LDT1) and light-duty trucks between 3751 and 5750 pounds loaded vehicle weight (LDT2). The total on-road fleet includes light, medium and heavy duty vehicles and motorcycles. The base scenario used the current California low emission vehicle (LEV II) standard. The more stringent control scenario modified the emissions inventory where all new passenger cars and light duty trucks in the SoCAB in year 2016 achieved Super Ultra-Low Emission Vehicle (SULEV) tail pipe emissions, zero evaporative emissions and more stringent aggressive driving requirements. An analysis estimated regional emissions of Non-Methane Organic Gases (NMOG) modeled as reactive organic gases (ROG), NOx, and CO. Then, the effect on ozone concentrations in the SoCAB was assessed using an existing air quality model and South Coast Air Management District input files. 2.1. Emissions inventory and modeling The emission inventory modeling tool used for this study was CARB’s Emission Factors (EMFAC2007) model (CARB, 2006) to study LEV II and the more stringent control scenario FTP, evaporative and SFTP vehicle emissions. EMFAC2007 combined detailed information on California’s fleet of motor vehicles, roadway information, vehicle miles traveled and detailed emission factors to estimate the emission rates of important air pollutants. EMFAC can be used to calculate emissions for the state, county, air basin, or air pollution control district. For this study, emissions for the South Coast Air Quality Basin (SoCAB) were calculated. The SoCAB encompassed all of Orange County and the majority of Los Angeles County, as well as the urban portions of Riverside and San Bernardino Counties. EMFAC was designed with a “Default” setting which reflects the current projections and estimates for each model year from 1970 to 2040. Emission inventories for the years 2006 through 2030 were calculated. The percentage of the new light duty fleet meeting revised emission restrictions was increased and the other vehicle technology percentages were reduced, thus the number of vehicles in the fleet overall did not change. The base case EMFAC default vehicle fleet settings were modified to reflect the anticipated more stringent scenario phase-in percentages and emission requirements for FTP, evaporative and SFTP. The anticipated requirement for FTP emissions increased the amount of SULEV vehicles. The percentage of new vehicles meeting the SULEV standard in 2013, 2014, 2015 and 2016 were 59, 72, 86 and 100 respectively. Currently, most vehicles achieve the near-zero evaporation or partial zero evaporation categories. The per-test evaporative standards were translated into emissions per vehicle or per start emission factors and were used to calculate total evaporative emissions for a population of near-zero evaporative emissions vehicles in EMFAC2007. A small fraction of vehicles, such as electric vehicles, belong to the zero evaporation category. Zero evaporation vehicles are not associated with any fuel-related evaporation, but are associated with evaporation from non-fuel components, such as wind shield wiper fluid, paint, etc. In EMFAC2007, the definition of zero emission
237
vehicles (ZEV) included only non-fuel related evaporation. Therefore, this vehicle type was used to model a vehicle with zero fuel-related evaporative emissions regardless of fuel type. However, EMFAC allows only passenger car and LDT1 vehicles to be modeled as ZEV vehicles. The LDT2 vehicles were maintained at default technologies. The more stringent scenario modeled new vehicles to have zero evaporative emissions in 2013, 2014, 2015 and 2016 with 25%, 50%, 75% and 100% respectively. Table 1 outlines the total light duty fleet by SULEV and zero evaporative technology for LEV II and more stringent scenario. Supplemental Federal Test Procedure (SFTP) standards are not explicitly modeled in the EMFAC2007 software. So, these testbased standards were translated to an emission inventory. SFTP conditions include the use of driving high speed/high load and using the air conditioning. The current SFTP standard in LEV II applies to new vehicles (4000 miles), while the more stringent control scenario SFTP (SFTP-2) was applied to in-use vehicles (150,000 miles). Next, the federal SFTP weighting scheme for the amount of time or miles corresponding to the driving conditions was determined to be appropriate. This was because California and Federal compliance for SFTP was intended to be harmonized. To calculate the effects of SFTP-2, the LEV II SFTP emission inventory was generated using EMFAC2007 for years 2006e2030. The vehicle emission technology mix for LEV, ULEV and SULEV was fixed for 2008 and beyond. For each vehicle emission technology, a ratio was derived based on the SFTP to SFTP-2 standard. The ratio was applied to vehicles for each technology group in 2012, 2013, 2014 and 2015 as 25%, 50%, 75% and 100% respectively. Using EMFAC2007 the emission inventory of LEV II and the more stringent scenario was determined and compared for total emissions, and then was used to separately analyze evaporative and SFTP requirements results. Table 2 shows the emission inventory modeling results for LEV II and the more stringent scenario total in the year the revised standards would have been completely phased-in, 2016, and in a year to represent long term results, 2030. For developing percentage comparisons, emission results were compared to their 2006 emissions. Total ROG, CO, and NOx emissions included exhaust and evaporative emissions for all on-road vehicles. Since exhaust emissions from light duty vehicles represent a fraction of total on-road emissions, the difference comparing LEV II to the more stringent control scenario for ROG, CO, and NOx emissions in 2030 were from zero (0) to five (5) percent. Changes to both evaporative and SFTP standards had nearly zero difference between the standards until 2016 because of the limited phased-in percentage. Evaporative emission standards only affect ROG emissions. So, by 2030, there was a 2% reduction in ROG when comparing near-zero evaporative emissions and the more stringent control scenario zero emission standard. Regarding the SFTP portion of the emission inventory study, in 2030 the difference between SFTP and SFTP-2 for NOx and ROG combined emissions had 1% reduction, while CO had 4% reduction.
2.2. Air quality modeling Air quality modeling was conducted for the SoCAB using existing models and input data sets. The U.S. EPA Community Multiscale Air Quality (CMAQ Version 4.6, released in October 2006) model (Byun and Schere, 2006; http://www.cmaq-model.org/) was used. Table 1 South Coast Air Basin light duty vehicle fleet percentage by technology for the LEV II and more stringent scenarios. 2006
2016
2020
2030
SULEV
LEV II More Stringent
5% 5%
15% 26%
20% 45%
24% 78%
Evaporative zero
LEV II More Stringent
1%e2% 1%e2%
1%e2% 12%
1%e2% 26%
1%e2% 53%
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Table 2 On-road mobile source emission inventory comparison between LEV II and the more stringent scenario. 2006
2016
2030
Base
Difference from base (%)
Difference from base (%)
LEV II
More stringent
More stringent compared to LEV II
LEV II
More stringent
More stringent compared LEV II
Total mobile source
ROG CO NOx
261 2614 549
51% 45% 49%
51% 43% 48%
0% 2% 1%
33% 26% 26%
32% 21% 25%
1% 5% 1%
Evaporative
ROG
261
51%
51%
0%
32%
30%
2%
SFTP
ROG þ NOx CO
810 2614
51% 50%
50% 50%
1% 0%
29% 28%
28% 24%
1% 4%
The CMAQ model configuration selected used the SAPRC-99 chemical mechanism (Carter, 2000) for the gas-phase chemistry, the Asymmetric Convective Model Version 2 for the vertical diffusion and global mass-conserving schemes to calculate horizontal and vertical advection. The photolysis rate look-up tables for this episode were created from the Total Ozone Mapping Spectrometer (TOMS) (ftp://toms.gsfc.nasa.gov/pub/eptoms/data/ozone/Y2005) ozone column data and used the CMAQ photolysis rate processor (JPROC). Air quality modeling input data sets were based on South Coast Air Quality Management District (SCAQMD) data sets used for their 2007 Air Quality Management Plan (AQMP) (SCAQMD, 2007). SCAQMD provided emission data for years 2005, 2014, and 2020. The data were available as gridded data and further divided by county and air basin. The domain was defined in a Lambert Conformal Conic Projection and consisted of 116 80 grid cells in the horizontal with a grid resolution of 5 km. The domain, shown in Fig. 1, covered 232,000 square kilometers (over 89,000 square miles). The northern boundary of the domain extended into Santa Barbara and Kern counties, while the southern boundary extended into Mexico. The eastern boundary of the domain was in the desert portions of San Bernardino and Riverside counties, while the western boundary extended approximately 200 km from the coastline in Los Angeles County. SCAQMD provided July 2005 initial and boundary condition output files, and the meteorological episode output files from the Mesoscale Model, MM5. The CMAQ ready meteorological files were prepared using the MeteorologyChemistry Interface Processor (MCIP), Version 3.3. The 34-layer MM5 output files were mapped into 17 CMAQ layers. The SCAQMD set of emission inventory files included area, biogenics, mobile, point and Mexico sources as well as stack parameter files, temporal allocation tables and speciation profiles. To prepare the
files for use in the CMAQ simulation, a method was developed to process inventory files, match the stack information and temporal profiles, speciate the pollutants to the SAPRC-99 chemical mechanism species, and finally generate three-dimensional NetCDF files. The different inventory categories were processed separately and later merged together to a single gridded file. The emissions were summed over all source categories and also summed over all model layers. To establish a reference point for the emission scenario simulations, to verify model performance, and to gain confidence in model predictions, the CMAQ model was used for a SoCAB episode in July 2005 when high concentrations of ozone were observed. The five-day episode used in the modeling was from July 14 through July 19, 2005 using modeling inputs from SCAQMD. The episode had typical southern California climate conducive to high air pollution episodes, i.e., stagnant flow, strong subsidence induced by synoptic scale high pressure, and subsequently limited vertical mixing and spatial dispersion (Lee et al., 2009). On July 15 the peak 8-hour ozone concentration of 143 ppb was observed while the model predicted 106 ppb. Thus, the model underpredicted the peak observed 8-hour ozone concentration on July 15 by about 25%. The model performance evaluation statistics are listed in Table S1. The model tends to underpredict ozone concentrations, with a normalized bias of 22%. This bias is higher than the EPA-recommended normalized bias of 15%. The normalized gross error is 30%, and is within the EPA-recommended goal of 35%. This tendency to underpredict peak 8-hour ozone concentrations is consistent with results from the SCAQMD application of Comprehensive Air Quality Model with Extensions (CAMx) for the 2007 AQMP (SCAQMD, 2007). As noted by Lee et al. (2009), the model performance was related to deficiencies in the meso-scale model (known as MM5) meteorological fields. Lee et al. (2009) made some modifications to the MM5 fields and found that these modifications resulted in improved air quality model predictions of ozone and CO concentrations for the SoCAB. Since results of this modeling were similar to the SCAQMD results, using these models, data and processes provided a scientifically credible approach for assessing future emission inventory changes on air quality. 3. Results, air quality
Fig. 1. Modeling domain for CMAQ simulations.
The potential impact of vehicle emissions on ozone concentrations in the SoCAB was predicted for years 2005, 2014 and 2020 using the LEV II emissions inventory in the CMAQ model. The first step was to predict the base year, 2005. Then the 2005 LEV II emission inventory was replaced with 2014 LEV II and then 2020 LEV II emission inventories. Next, the 2014 and 2020 LEV II emission inventories were revised with the more stringent control scenario emission inventories. Only varying the light duty vehicle emission inventory kept the model performance statistics constant
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and isolated the effect of changing light duty vehicle emissions. The predicted 8-hour average ozone concentrations for July 15, 2005 LEV II emissions are shown in Fig. 2a. Fig. 2b shows the predicted 8-h average ozone concentrations using 2005 meteorology and replacing the emissions inventory with 2014 emissions inventory. Fig. 3a shows the percent change in predicted 8-hour ozone concentrations between 2005 and 2014. Fig. 3b represents the percent change in predicted 8-h ozone concentrations between 2005 and 2020. The spatial distribution of CO, NOx and ROG emissions resulted in reducing emissions in 2014 and 2020 when compared to 2005. Ozone concentrations decrease up to 28% over large areas of the basin. However, since the western portions of the basin NOx emission reductions were larger than the reductions in ROG emissions, as shown in Table 2, and because the western portion of the basin is VOC- sensitive, the predicted ozone concentration for this region would increase 30% or more in both 2014 and 2020 compared to 2005. Next, replacing LEV II emission inventory with the more stringent control emission inventory predicted ozone concentrations to change between 1% to 0.8%, in 2014 and 2020 as shown in Figs. 4 and 5 respectively. Next, changes to ozone concentration due to changing separately the evaporative emission and SFTP-2 standards were explored. As previously described, evaporative emission standards do not affect NOx emissions. In 2014, changing only the evaporative portion of the LEV II to the more stringent control scenario’s emission inventories resulted in negligible ROG emission reduction
Fig. 3. a: Relative change in predicted 8-h average surface O3 concentrations when 2005 emissions (Fig. 2a) are replaced by 2014 LEV II emissions (Fig. 2b). b: Relative change in predicted 8-h average surface O3 concentrations when 2005 emissions (Fig. 2a) were replaced by 2020 LEV II based emissions. Predicted ozone concentrations change from by increasing in the green, yellow and red areas and decreasing in the blue areas.
and, subsequently, negligible ozone concentration change. In 2020 compared to 2014 the more stringent control evaporative scenario resulted in up to 2% decrease in ROG emissions, and subsequently, decreased 8-hour average ozone concentrations less than 0.2%. Compared to the LEV II SFTP emissions for 2014 and 2020, SFTP-2 resulted in reducing ROG plus NOx and CO emissions. Because ozone formation in the South Coast Air Basin, particularly in the western and central portions of the basin, is VOC-sensitive with respect to ozone formation, the 8-h average ozone concentrations in the western portion of the basin increased up to 2% and in other areas decreased up to 1% in 2014 and 2020 respectively.
4. Summary and discussion
Fig. 2. a. Predicted 8-h average surface O3 concentrations on July 15, 2005. b. Predicted 8-h average surface O3 concentrations on July 15, 2005 using 2014 LEV II emission inventory.
This paper compared emissions from passenger cars and light duty trucks under the current California Low Emission Vehicle (LEV II) standards to a control scenario which was anticipated in 2008 to become LEV III (referred to as “more stringent control” in this paper) and determined if the scenario would result in additional improvements to air quality in California’s South Coast Air Basin. The air quality modeling was done using the Community Multi-scale Air Quality Model (CMAQ) for years 2005, 2014 and 2020 and emission inventories supplied by SCAQMD. The study was applied to passenger cars and light duty trucks in the South Coast
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Fig. 4. Relative change in predicted 8-h average surface O3 concentrations when the 2014 LEV II emission inventory results were replaced with the 2014 more stringent case scenario. Predicted ozone concentrations change in 2014 between LEV II and the more stringent scenario by increasing in the green areas and decreasing in the blue areas.
Air Basin. Emission inventories and ozone concentrations were studied for the current California LEV II standards and a more stringent control scenario. The existing standards and the more stringent control scenario had nearly identical emission inventory and ozone concentration results. The resulting emission reductions for on-road vehicles averaged across the South Coast Air Basin showed the more stringent scenario compared to the current California Low Emission Vehicle (LEV II) regulations would have 1% for NOx, 1% for ROG and 5% for CO reduction in 2030. Relative to 2005, in 2014 and 2020 the LEV II and more stringent control scenario show ozone concentrations decrease over large areas of the basin. However, ozone levels in the western portions of the basin increase because these areas are VOC-sensitive and the reductions in NOx emissions are larger than VOC reductions. Projected ozone increases in some areas and decreases in other areas are a result of emission changes, meteorology and photochemistry. When VOC levels are high relative to NOx, in areas with large biogenic VOC emissions, ozone is reduced by NOx reductions and increased by NOx increases. Such conditions are called “NOx -limited” or “NOx -sensitive.” Predicted ozone reductions in the non-western SoCAB area are likely achieved by
reducing NOx. However, when NOx levels are relatively high and VOC levels are relatively low, increases in NOx can decrease ozone, because NO reacts directly with ozone and NO2 terminates radicals, forming nitric acid, which is removed from the system or forms particulate nitrates. Such conditions are called “VOC-limited,” “VOC-sensitive” or “NOx -saturated.” Under these conditions, VOC reductions are effective in reducing ozone, but NOx reductions can increase ozone under certain circumstances. Hence, decreasing NOx more than decreasing VOC results in ozone increases (Cook et al., 2010). The ozone increase predicted in the western portion of the SoCAB is because the area is likely VOC-sensitive and is projected to experience NOx decreases. Separate analysis of emission changes due to revising the evaporative and SFTP standards was performed. The evaporative standard comparison projected the more stringent control scenario versus LEV II for 2020 would have additional reductions of about 2% in ROG emissions compared to the current standard; subsequently this produced less than 0.2% reduced ozone concentrations. The current SFTP and more stringent control scenario SFTP-2 would potentially reduce emissions for CO, NOx and ROG for on-road vehicles across the SoCAB. Again, the NOx emissions are reduced more than the VOC emissions. So, the scenario resulted in up to 1.7% increased ozone concentration in the VOC-sensitive western portion of the Basin, and decreased up to 1% in NOx-sensitive areas. The current LEV II and future more stringent control scenario requirements will achieve emission reductions in the SoCAB; however, the results may not have a desired affect on ozone in the entire SoCAB. There are limitations and uncertainties in determining emission inventories, performing emission inventory modeling and air quality modeling. This study provided a relative comparison of current versus future standards without changing other variables. Acknowledgements The work reported herein was performed by Atmospheric and Environmental Research, Inc. (AER) under a contract from Toyota Motor Engineering and Manufacturing North America, Inc. (TEMA). While the work was performed by AER, the conclusions are those of the authors and do not necessarily reflect the views of AER. Appendix. Supplementary data Supplementary data associated with this article can be found in the online version, at doi:10.1016/j.atmosenv.2011.11.010. References
Fig. 5. Relative change in predicted 8-h average surface O3 concentrations when the 2020 LEV II emission inventory results were replaced with the 2020 more stringent case scenario. Predicted ozone concentrations change in 2020 between LEV II and the more stringent scenario by increasing in the green areas and decreasing in the blue areas.
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