The Ongoing Challenge of Managing Carbon Monoxide Pollution in Fairbanks, Alaska Interim Report (2002) / Chapter Skim
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1 Sources and Effects of Carbon Monoxide Emissions
1 Sources and Effects of Carbon Monoxide Emissions
Pages 19-48
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From page 19... ...
. The locations that continue to have high concentrations of CO tend to have topographical or meteorological characteristics that exacerbate pollution; for example, strong temperature inversions or the existence of nearby hills that inhibit wind flow may limit pollutant dispersion.
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From page 20... ...
The committee will consider interrelationships among emissions sources, patterns of peak ambient CO concentrations, and various CO emissions-control measures in such areas. In addition, the committee will consider ways to better understand relationships between episodes of high ambient CO and personal exposure, the public-health impact of such episodes, and alternative ways to measure progress in controlling ambient CO.
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From page 21... ...
Control of stationary source contributions to CO air quality will also be considered. · Assessing the effectiveness of CO emissions-control programs, including comparisons among areas with and without unusual topographical or meteorological conditions.
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One subject of particular interest will be the extent to which areas other than Fairbanks would benefit from stricter vehicle-certification standards that control emissions produced by vehicle starts at Tow temperatures. HEALTH EFFECTS OF CO Clinical and Epidemiological Studies of CO Effects CO affects human health by impairing the ability of the blood to bring O2 to body tissues.
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From page 23... ...
COHb levels in healthy individuals not recently exposed to high concentrations of ambient CO are 0.3 to 0.7%. Exposure to high concentrations of ambient CO can result in concentrations of COHb of 2% or higher if the exposure lasts long enough (hours)
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From page 24... ...
disorders and cognitive impairments due to Tong-term, low-concentration CO exposures have been hypothesized in part on the basis of extrapolation from the known acute effects of high-dose CO poisoning and the concomitant subacute and delayed neuropsychological sequelae. In clinical experiments on healthy volunteers, controlled CO exposure was associated with subtle alterations in visual perception when COHb concentrations were above 5°/O (McFarland 1970; Horvath et al.
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From page 25... ...
Although less conclusive, there is evidence that attainment of the CO standards will also decrease morbidity from pulmonary disease, neurological disease, fetal Toss, and childhood developmental abnormalities. These health benefits translate into economic savings associated With avoided health care and avoided worktime Tosses as well as intangible savings in life quality.
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From page 26... ...
(1) Although most areas show a bimodal diurnal pattern with respect to ambient CO concentrations, Fairbanks, Alaska, the focus of this interim report, typically shows a continuous increase throughout the day, with 1-h average CO concentrations peaking at 5:00-6:00 p.m.
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From page 27... ...
Incomplete combustion in mobile sources is estimated to contribute a substantial fraction to the emissions of several toxic air pollutants, including benzene, 1 ,3-butadiene, and aldehydes (EPA 2001c)
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, as directed by the Clean Air Act (CAA) , established health-based air quality standards for CO in 1971.
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Sources and Effects of Carbon Monoxide Emissions 29 within a year are considered violations of the standard.4 The standards have been periodically reviewed on the basis of new scientific findings as mandated by the CAA. The most recent review was published in 2000, when the standards were reaffirmed (EPA 2000a)
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From page 30... ...
However, unusual meteorological conditions or unexpected increases in emissions (in the case of Fairbanks, construction of a trans-Alaska naturalgas pipeline or substantial missile defense facilities) could prevent those areas from maintaining compliance.
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From page 31... ...
Such temperature inversions inhibit vertical mixing be cause less-dense warm air rests above colder, denser air. The temperature inversion therefore defines the vertical limit of mixing.
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Sources and Effects of Carbon Monoxide Emissions 33 , it.
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Indeed, regions under high-pressure systems, where subsidence and the advection of warm air aloft can both be present (Figure I-5) , typically experience inversion conditions.
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From page 36... ...
In contrast, southwestern California experiences inversions at higher altitudes because of strong subsidence associated with descending air in the subtropical eastern Pacific Ocean high-pressure system. Inversions in southwestern California are high because, in contrast with the winter situation in Fairbanks, sunshine on the surface permits vertical mixing in the atmospheric layer near the surface.
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From page 37... ...
It is common to calculate the annual emissions of CO in nonattainment areas; the estimates are used to compare emissions in various years and locations, assess the effectiveness of air pollution policies, and predict the impact of future projects on emissions. Determining an emissions inventory requires that all major sources of a pollutant be identified, that the releases from the sources be quantified, and that the releases be summed to determine the total mass emitted in the defined area.
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From page 38... ...
CO EMISSIONS FROM VEHICLES The primary source of CO from vehicles is the incomplete combustion of gasoline in engine cylinders. The fuel-oxidation process (combustion)
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From page 39... ...
Sources and Effects of Carbon Monoxide Emissions 39 TABLE I-2 National CO Emissions Inventory Estimates for 1999 Source Category Point- or Area-source fuel combustion Electric utilities Industry Residential wood burning Other Thousands of Short Tons 5,322 445 1,178 3,300 399 7,590 1,081 1,678 366 3,792 599 49,989 27,382 16,115 4,262 2,230 25,162 3,616 11,116 1,002 4,259 5,169 9,378 6,152 Industrial processes Chemical and allied product manufacturing Metals processing Petroleum and related industries Waste disposal and recycling Other industrial processes r _ Onroad vehicles Light-duty gas vehicles and motorcycles Light-duty gas trucks Heavy-duty gas vehicles Diesels Nonroad engines and vehicles Recreational Lawn and garden Aircraft Light commercial Other Miscellaneous Slash or prescribed burning Forest wildfires Other 2,638 588 Total Source: EPA 2001a.
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From page 40... ...
Since the middle 1980s, modern computer-controlled engines have used electronic fuel injectors rather than carburetors to deliver fuel to cylinders in automobiles and most light-duty trucks. Using closed-Ioop control, the engine computer system reads the signal from an O2 sensor in the exhaust system and adjusts the air-to-fuel ratio to help maintain stoichiometric combustion.
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From page 41... ...
When a significant number of sensors become inoperative, the OBDU system will also have less ability to alert vehicle owners of potential emissions-system failures. Cold-Start Emissions Under cold-start conditions, the engine computer commands the fuel injectors to add excess fuel to the intake air to ensure that enough fuel evaporates to yield a flammable mixture in the engine cylinders.
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From page 42... ...
The most important and effective vehicle emissions-controT strategy for CO has been the nationwide introduction in 1980 and 198~ of more stringent vehicle certification requirements designed to reduce exhaust emissions of CO, HCs, and NOX. In 1981, EPA introduced emissions certification standards for passenger cars that provided a 3.4-g/mile (ml)
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From page 43... ...
The lower-temperature cold-start test represents only the upper boundary of the temperature range of concern in Fairbanks. Furthermore, some emissions-control-system sensors and actuators are inaccurate at very low temperatures, and the engine computer might ignore their input signals until the engine warms up is.
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From page 44... ...
The simplest models assume a direct correlation between emissions and ambient pollutant concentrations; the most complicated models resolve temporal and spatial variations in pollutant concentrations and include the effects of meteorology, emissions, chemistry, and topography. Models are also characterized by the size of the problem they address: microscaTe models simulate pollution from an intersection or point source, mesoscale models simulate metropolitan or multistate pollution, and large-scare models simulate continental or global pollution.
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From page 45... ...
In the case of modeling of intersections, the emissions inventory may be derived from information about traffic patterns, mean speeds, and vehicle-fleet composition. Larger cities have also used Gaussian dispersion models to evaluate the air quality effects of increasing road capacity or other large construction projects (EPA 1992~.
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From page 46... ...
The most complicated models used for attainment demonstrations simulate how a pollutant concentration varies with time and space over an entire urban area. These numerical predictive models, generally intended for mesoscaTe analysis, can simulate emissions from multiple sources and the dispersion, advection, and photochemical reactions of gaseous pollutants in the atmosphere.
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From page 47... ...
Predictions of CO, for example, can be straightforward in the National Weather Service Eta Model, which has a horizontal grid framework of ~ 2 x ~ 2 On over the contiguous United States. Despite advances in air quality modeling capabilities over the last 30 y, many improvements are still possible and needed, particularly in the numerical predictive models, which are used more widely than process numerical models.
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From page 48... ...
One such location is Fairbanks, Alaska. The task of the Committee on Carbon Monoxide Episodes in Meteorological and Topographical Problem Areas was to assess approaches for predicting, assessing, and managing episodes of high CO concentrations in meteorological or topographical problem areas.
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