Managing Carbon Monoxide Pollution in Meteorological and Topographical Problem Areas (2003) / Chapter Skim
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3. Management of Carbon Monoxide Air Quality
3. Management of Carbon Monoxide Air Quality
Pages 100-148
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From page 100... ...
Achieving and maintaining the NAAQS requires monitoring ambient CO, developing emissions inventories, implementing emissions regulations and related controls, and tracking progress. This chapter discusses the primary air quality management elements needed to achieve those objectives the basic emissions control strategies used to reduce emissions and the monitoring and modeling tools used to characterize and assess the magnitude of the problem.
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From page 101... ...
For example, the Alaska Department of Environmental Conservation in its most recent SIP for Fairbanks attributed over 70°/O of total emissions reductions over the ~ 995-2001 time period to more stringent federal new-vehicle emissions standards (ADEC 20011. Table 3-1 shows emissions standards for passenger cars and light-duty trucks.2 CO emissions standards have dropped by over an order of magnitude since their inception emissions from new passenger cars have fallen from 84 grams per mile (g/mi)
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made these achievements possible. This is in contrast to in-use emissions controls, such as vehicle emissions inspection and maintenance (~/M)
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From page 103... ...
Tier 2 requires each manufacturer to meet a sales-weighted "corporate average NOX standard" of 0.07 g/mi. Lowering fuel sulfur content, which is discussed in the section on in-use emissions controls, is also an integral part of the Tier 2 strategy.
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certification limits for their respective bin. NOX emissions standards for the three bins would then be sales-weighted and compared with the average NOX standard of 0.07 g/mi.
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standard.3 Although the current 3The CAAA90 authorized California, which has the nation's worst air pollution problems, to impose stricter vehicle emissions standards than those for the rest of the nation. California's low emissions vehicles (LEV)
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From page 106... ...
This increase in vehicle durability will slow the penetration of vehicles with newer emissions control technologies into the fleet. In the meantime, the ongoing improvements resulting from HC standards under Tier 1 and NLEV, the cold-start CO standards, the increased durability required under Tier 1, and the introductions of the SFTP will continue to encourage the downward trend in CO emissions from light-duty vehicles in advance of Tier 2.
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From page 107... ...
In addition, some emissions control strategies for controlling cold-start emissions are particular to HCs and do not improve CO emissions. Some of the lowest-emitting vehicles in California (called super ultra-Iow emissions vehicles tSULEV]
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From page 108... ...
108 Managing CO in Meteorological and Topographical Problem Areas 1996 California Low Emissions Vehicle 15.0 14.9 14.8 14.7o 14.6 ~ 14.5 2 14.4 14.3 14.2 14.1 14.0 15.0 ~ 14.9 ~ 14.8 ~ O 14.7._ 14.614.514.414.3 ~ 14.2 ~ 14.1 ~ 14.0 ~ .
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From page 109... ...
Since 1994 new cars and the lightest category of light-duty trucks (LDT1) have been required to meet a CO limit of 10 g/mi on the federal test procedure (FTP)
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From page 110... ...
Certification to this new cycle will be phased in during the 2000 and 2004 model years. This test procedure should ensure that vehicle emissions control systems will provide improved emissions control over a wider range of vehicle speeds and loads.
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This involves testing a preproduction prototype to prove that it meets applicable model year emissions standards and durability-deterioration requirements. The certificate requires the manufacturer build every vehicle (or engine)
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Clean fuels programs and I/M programs are the mainstays of nationwide in-use vehicle controls. In some regions, where winter temperatures are frequently below 20°F and cold-starts contribute substantially to the regional emissions inventory, engine preheating also provides valuable emissions reductions.
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An NRC committee that recently looked at I/M programs concluded that they generally have not achieved the emissions reductions originally projected (NRC 2001~. For example, in-program and remote4A loaded-mode test, such as the IM240 or the FTP, involves testing vehicle emissions while the vehicle is on a dynamometer that simulates the load a vehicle is under during on-road operation.
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From page 114... ...
for later analysis. In a garage setting, mechanics can download the OBDU fault codes from the onboard computer with a diagnostic analyzer or "scan tool." The codes identify emissions control systems and components that are malfunctioning.
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Remote sensing is a technique that measures emissions from individual vehicles as they drive by a roadside sensor. It offers the possibility of testing vehicle exhaust emissions without requiring the vehicle's presence at a testing facility, though the test is only for a relatively short time (approximately ~0.5 seconds)
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From page 116... ...
Other vehicles may have been repaired, but owners may not have reported that on the survey. Besides application as a testing device, remote-sensing measurements can be useful for characterizing vehicle emissions, including average emissions by mode!
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A 1997 study of the winter oxyfuels program initiated by the White House Office of Science and Technology Policy concluded that at temperatures above 50°F, CO emissions from most vehicles were reduced by about 3-6% per weight percent oxygen (NSTC ~ 997~. CO emissions reductions of 3-7% are predicted by EPA's MOBILES model for the 2010-2015 fleet, mainly because of reduced emissions from pre-1994 vehicles, cold starts, and malfunctioning vehicles.5 Emissions reductions are generally lower in newer-technology vehicles (those with closed-Ioop fuel control and three-way catalysts)
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From page 118... ...
and in reduction of exhaust emissions of VOCs and air tonics, including benzene. In practice, this translates into an RFG aromatic content of <25%, and fuel sulfur concentrations of about 30 ppm (compared to >350 ppm for non-RFGs)
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Hybrid Gasoline-Electric Vehicles Hybrid vehicles combine a conventional internal combustion engine with an electric motor. The internal combustion engine can be run on various alternative fuels; however, this discussion relates to those vehicles powered by a normal gasoline-fueled engine alternating or in concert with an electric motor, with the battery system being charged by the gasolinepowered engine.
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17230 t200 11~. The EPA analyses show that programs already in place, such as the reformulated gasoline program, the national low-emissions vehicle program, and the Tier 2 emissions standards and fuel sulfur controls, will yield significant reductions of mobilesource air tonics.
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Transportation Control Measures Transportation control measures (TCMs) are actions designed to change travel demand or vehicle operation characteristics to reduce motorvehicle emissions, energy consumption, and traffic congestion.
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TS1 strategies attempt to reduce emissions by changing the physical infrastructure of the road system to improve traffic flow and to reduce stop and go movements. In contrast, TDM strategies attempt to reduce the frequency and length of automobile trips by changing driver behavior using regulatory mandates, economic incentives, voluntary programs, and education campaigns.
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TRAFFIC FLOW IMPROVEMENTS Strategies that enhance the efficiency of a roadway system, without adding capacity, including traffic signalization, traffic operations, and enforcement and management.
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The success of voluntary control strategies depends on consumer behavior and the availability of alternatives, so public education and exhortation programs figure prominently in all of these strategies. In a recent review of the Congestion Mitigation and Air Quality Tmprovement Program (CMAQj, which funds TCMs in ozone and CO nonattainment areas, the Transportation Research Board (TRB 2002)
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For example, although Fairbanks has a fairly active public-information campaign concerning the connection between vehicle plug-ins at temperatures above 0°F and improved air quality, most individuals responding to a survey said they plugged in for ease in starting their vehicles (ADEC 2001~. Public education programs have been implemented in numerous metropolitan areas throughout the United States by local, regional, and state governments as well as nonprofit organizations such as the American Lung Association, with help from the federal government.
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, and 12 were not.6 During the same period, three exceedances occurred that were not forecast. In 1997, EPA established a policy for incorporating voluntary measures, such as public education programs and episodic control programs, into state implementation plans (SIPs)
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and financial incentives to encourage development within existing urbanized areas, which is conducive to public transit, biking, and walking. Smart growth strategies have the potential to reduce vehicle travel by reducing trip distances and reliance on the car (EPA 2001i)
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It is thus possible that smart growth strategies will prove effective in reducing regional levels of ozone but at the time result in the creation of new areas of high CO and related pollutants. However, given the continuing reduction in CO emissions through improvements in vehicle controls, the possibility that such areas would produce CO exceedances seems remote for most locations.
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MONITORING, MODELS, AND INVENTORIES There are three important tools for air quality management of CO and other pollutants: monitors, models, and inventories. Monitors provide measurements of ambient pollutant concentrations.
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tool in conformity determinations when compared with the emissions budget (Howitt and Moore 1999~. CO emissions rates for inventories or other purposes are seldom measured directly; they are estimated using models and/or emissions factors.9 Models are verified and improved by comparing their results with measurements of actual concentrations.
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Permanent Monitoring Stations Fong-term, permanent stations are used for monitoring in most large urban areas in the United States as part of EPA's ambient air monitoring
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Whereas the results from short-term monitoring tend to be used for planning and research, data from long-tenn monitoring stations can have a direct impact on federal policy. Because these stations are used to determine air quality trends and to establish attainment status, the measurements made there play a large role in federal air quality management.
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Accordingly, model development and appropriate use are crucial to the overall air quality management process. Models for mobile sources, stationary sources, and regional impacts are prescribed by EPA in Appendix W of the Code of Federal Regulations, Title 40, Part 51.
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. Although direct traffic counts can be used to estimate existing emissions, travel-demand techniques are necessary to predict future traffic volumes.
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Emissions Factors Models The emissions inventory is an important tool for estimating the relative impacts of emissions controls. Inventories predict the total mass emitted annually from all contributing sources of a particular pollutant, such es CO.
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2002~. Concerns over these issues prompted a recent NRC committee charged with reviewing MOBILE to recommend that enhanced model evaluation studies, in tandem with uncertainty studies, begin immediately and continue throughout the long-term evolution and development of mobile-source emissions models (NRC 2000; Holmes and Russell 2001~.
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, Version 4.~3 This computer model includes emissions rates for most aircraft types, ground support equipment, motor vehicles (based on MOBBED, typical stationary sources at airports, and training fires. The model requires operational data for each of these sources and generates an emissions inventory for the airport.
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It is clear that emissions inventories for stationary sources need improvement. Air Quality Models Air quality modeling is an essential element of air quality management.
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, Gaussian dispersion, and numerical predictive models. Rollback Models The simplest of the three models used for attainment demonstrations is the statistical rollback mode]
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, along with traffic volumes, roadway geometries, and intersection information, are used to determine the emissions along a roadway. Dispersion modeling then includes transport and mixing to calculate local concentrations.
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Even better research tools than the numerical predictive models described above (such as Models-3 and the UAM) are process numerical models, which allow processes specific to air quality modeling and meteorology to be coupled within a single computational framework.
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Though box models are not used in attainment demonstrations, they are particularly useful to understand how various emissions scenarios and meteorological conditions affect pollutant concentrations. For example, a box model for CO in Anchorage, Alaska, has been used to quantify how mechanical turbulence from roadway traffic might increase the mixing height and reduce CO concentrations on severe-stagnation days compared with concentrations observed in residential neighborhoods (Morris 2001~.
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Despite advances in air quality modeling capabilities over the last 30 years, many improvements are still possible and necessary. One problem is that the vertical and horizontal resolution of models is too coarse to capture the variability in pollutant concentrations, which is necessary to identify local hot spots and is important for determining local concentrations downwind of hot spots.
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Statistically Robust Methods to Assist in Tracking Progress The air quality models described above assess the effectiveness of emissions controls and the prospects for attaining the CO standard by representing critical processes within a physically based model of the system. An alternative to those physical models is to take a statistical approach assessing the relationship among human activities, CO emissions, meteorology, and ambient air quality, as described below.
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From page 145... ...
The natural logarithms of the corrected peak 8-hour average CO concentrations were normally distributed; the 8-hour averages themselves were not. By estimating future emissions inventories for the years 2002-2013, based on projected fleet composition and VMT, and assuming that the lognormal distribution would hold for future years, Reddy was able to calculate the probability of an exceedance on a single day of the first week in February (P~ ~ for the future years.
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How can the impact of meteorological trends on the observed concentrations be removed in order to assess the impact of emissions controls and to show true progress towards meeting air quality standards in the future, when meteorological conditions may not tee so favorable? One must "de-trend" the observations.
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For example, in Fairbanks, a nonlinear response to temperature is expected because CO concentrations appear to be highest at about -20°F to 20°F, not at much lower or much higher temperatures. This approach is convenient for local air quality management organizations because it requires relatively little data (e.g., a long-term record of CO concentrations and meteorological variables such as temperature and windspeed would suffice, though more factors are useful)
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148 Managing CO in Meteorological and Topographical Problem Areas probabilities of exceeding the NAAQS for CO at various emissions levels. From that, the necessary level of emissions can be identified in a more statistically robust fashion.
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