Wolff G.T.,Air Improvement Resource Inc. |
Kahlbaum D.F.,Air Improvement Resource Inc. |
Heuss J.M.,Air Improvement Resource Inc.
Journal of the Air and Waste Management Association | Year: 2013
A national analysis of weekday/weekend ozone (O3) differences conducted using 1997-1999 data found that many urban areas experienced at least 5% higher 8-hr maximum O3 concentrations on weekends than on weekdays even though emissions of precursors were significantly lower on weekends. This phenomenon was observed mostly in urban areas in the Northeast, Midwest, and coastal California. A similar analysis using 2008-2010 O3 data shows that this phenomenon has mostly vanished. From 1997-1999 to 2008-2010, the percentage of U.S. monitoring sites that experienced 95th percentile daily 8-hr maximum average O3 concentration on weekends that were 5% or more higher than on weekdays declined from about 35% to less than 5%. At the same time the percentage of sites that experienced higher weekday concentrations increased from 3% to about 27%. The majority (68%) of the sites, however, exhibited little sensitivity to the weekday/weekend emission changes as they had similar (±5%) O3 on weekdays and weekends. Similar trends were observed for the three other O3 metrics examined: the 95th percentile of the 1-hr maximum and the April-September means of the 1-hr and 8-hr daily maxima. Over this time period, U.S. emissions of O3 precursors declined significantly. However, a greater decline in nitrogen oxides (NOx) emissions has caused an increase in the volatile organic compounds (VOC)/NOx emission ratios and it appears that this is the reason for the shift away from higher weekend O3 concentrations. In areas where weekend emissions of ozone precursors are lower than on weekdays because of mainly lower motor vehicle emissions, an inadvertent test of ozone control strategies occurs. Such a test provides information on how control strategies that produce emission changes similar to those that occur on weekends affect ozone concentrations. In the late 1990s, lower NOx emissions on weekends resulted in higher levels of ozone in many urban areas. Emission controls that have been enacted since then appear to have eliminated that phenomenon in most urban areas. However, most areas now indicate that weekend emission reductions now have little effect on ozone concentrations at most sites. © 2013 Copyright 2013 A&WMA.
Kim S.,Michigan State University |
Dale B.E.,Michigan State University |
Heijungs R.,VU University Amsterdam |
Heijungs R.,Leiden University |
And 3 more authors.
Biomass and Bioenergy | Year: 2014
In the Renewable Fuel Standard (RFS2) program, the United States Environmental Protection Agency (U.S. EPA) has used partial equilibrium models to estimate the overall indirect land use change (iLUC) associated with the biofuel scenario mandated by the Energy Independence and Security Act of 2007 (EISA). For regulatory purposes, the U.S. EPA "shocks" (changes) the amount of each biofuel in the economic models one at a time to estimate the threshold values for specific biofuels (single-shock analysis). The primary assumption in the single-shock analysis is that iLUC is a linear process with respect to biofuels, i.e., that interactions between different biofuels are trivially small. However, the assumption of linearity in the single-shock analysis is not appropriate for estimating the threshold values for specific biofuels when the interactions between different biofuels are not small.Numerical results from the RFS2 program show that the effects of interactions between different biofuels are too large to be ignored. Thus, the threshold values for specific biofuels determined by the U.S. EPA are scenario-dependent and value choice-driven. They do not reflect real impacts of specific biofuels. Using scenario-dependent values for regulation is arbitrary and inappropriate. Failure to deal appropriately with interactions between different biofuels when assigning iLUC values to specific biofuels is a mathematical and systematic flaw; it is not an "uncertainty" issue. The U.S. EPA should find better ways to differentiate the contribution of one biofuel versus another when assigning iLUC values or find better means of regulating the land use change impact of biofuel production. © 2014 Elsevier Ltd.
Darlington T.L.,Air Improvement Resource Inc. |
Kahlbaum D.,Air Improvement Resource Inc. |
Van Hulzen S.,POET LLC |
Furey R.L.,Furey Fuels Consulting LLC
SAE Technical Papers | Year: 2016
In 2008-2009, EPA and DOE tested fifteen 2008 model year Tier 2 vehicles on 27 fuels. The fuels were match-blended to specific fuel parameter targets. The fuel parameter targets were pre-selected to represent the range of fuel properties from fuel survey data from the Alliance of Automobile Manufacturers for 2006. EPA's analysis of the EPAct data showed that higher aromatics, ethanol, and T90 increase particulate matter (PM) emissions. EPA focused their analysis only on the targeted fuel properties and their impacts on emissions, namely RVP, T50, T90, aromatics, and ethanol. However, in the process of fuel blending, at least one non-targeted fuel property, the T70 distillation parameter, significantly exceeded 2006 Alliance survey parameters for two of the E10 test fuels. These two test fuels had very high PM emissions. In this study, we examine the impacts of adding T70 as an explanatory variable to the analysis of fuel effects on PM. We then compare an emissions model using just the EPA variables to our new emissions model using T70. Results indicate that for the EPAct test program, the T70 distillation parameter is a better predictor of cold start PM emissions than the other distillation parameters, and a cold start emissions model that includes T70 does not include an ethanol term for cold start emissions. Further results indicate that if T70 is added to the Bag 1 EPAct model and used in EPA's MOVES2014 emission inventory model, increased ethanol levels beyond E10 are predicted to reduce PM from on-road motor vehicles in the U.S. © Copyright 2016 SAE International.