The Ongoing Challenge of Managing Carbon Monoxide Pollution in Fairbanks, Alaska Interim Report (2002) / Chapter Skim
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2 Fairbanks Case Study
2 Fairbanks Case Study
Pages 49-108
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From page 49... ...
The Fairbanks North Star Borough stands out as the only serious CO nonattainment area with a population under ~ 00,000 and little industry. In Fairbanks, vehicle emissions, meteorology, and topography combine to produce conditions conducive to high ambient CO concentrations.)
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From page 50... ...
This chapter discusses the CO problem in Fairbanks, beginning with the physical and demographic characteristics of the area; the management strategies used to control the CO problem; and a simple air quality model for coupling meteorology and vehicle emissions. Lessons learned from the Fairbanks case are summarized in the committee's findings end recommendations in the Summary of this interim report and serve as a basis for the development of a final report that will include assessments of other CO problem areas.
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From page 51... ...
A surface inversion due to net energy loss from the surface occurs in the few meters closest to the ground, although the weaker inversion topping it may be caused by subsidence or transport of warmer air aloft. The combination of high albedo (reflection of sunTight due to snow cover)
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From page 52... ...
Three limited datasets support such high inversion strengths: . Traverse data of temperature differences between vehicle-mounted thermistors 0.5 m and 2 m above the ground showed inversions of about ~ °C/~.5 m (67°C/100 m)
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From page 53... ...
· Borough measurements of temperatures 3, 10, and 23 m above the ground are taken on a meteorological tower in the downtown area (Figure 24~. Inversion strengths of as much as about 30-40°C/IOO m have been measured on the tower during episodes.
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From page 54... ...
Finally, the combination of strong ground-level inversions with surface temperatures and winds that probably vary widely over horizontal distances of 0.l hen suggests that inversion strength (and probably mixing height) may be highly variable spatially (Holmgren et al.
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From page 55... ...
Asterisks indicate CO monitoring sites; triangles indicate where vehicles are counted. The meteorological tower is indicated by a dot.
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From page 56... ...
measured during an exceedance of the CO standard on November 19, 1999. The inversion strengths were calculated from temperature measurements taken on the meteorological tower.
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From page 57... ...
The average hourly traffic counts observed at three locations in Fairbanks (see Figure 2-4) are shown in Table 2-1 for the CO seasons of 1995-1996 through 2000-2001.
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From page 58... ...
Although the three monitoring sites satisfy EPA's monitoring guidelines, they are located quite close together and therefore do not provide much information about the spatial distribution of CO concentrations across the borough. The following analysis of observations at these three sites is limited in that respect, and similar analyses should be conducted in the future with data that are more spatially representative.
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From page 59... ...
It is thought that the high emissions from cold starts of vehicles that had not been plugged in contributed to the exceedances. CO exceedances in the borough are a function of location.
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From page 60... ...
Variability in CO as a function of altitude may reflect heterogeneity in the mixing-layer height. However, it is not known how large the area of high CO is or generally how CO concentrations vary spatially in the nonattainment area.
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From page 61... ...
Source: Data provided by Paul Rossow, Fairbanks North Star Borough. Recent CO Trends Concentrations of CO measured at the three monitoring stations in downtown Fairbanks during November through February (the CO season)
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From page 62... ...
Across all three monitoring stations, the summary measures decrease over the 6-y period. For each summary measure and each monitoring station, the decreasing trend was summarized into an annual change rate, defined as the slope coefficient for the linear regression of the six values for the annual summary measure on time (see Table 2-2~.
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From page 63... ...
63 it; d ·_ Ct U
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From page 65... ...
As shown in Table 2-3, the ratio of the annual change rate to the value of the summary measure in 1995-1996 is about 7% for all the measures at all three sites. That implies that for the 75thpercentile end higher, CO concentrations have been declining by about 7% each year in the Fairbanks nonattainment area over the period 1995-1996 to 2000-2001.
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From page 67... ...
67 au CQ ¢ U
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From page 68... ...
68 x · 0;, _ o o A it, .= ._ m 0 V C)
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From page 69... ...
Empirical modeling attempts to discern statistically significant relationships between an outcome variable and various predictor variables. In particular, an empirical model was developed using the I-h average CO concentration at the Hunter School monitoring site7 as the dependent variable and the following predictors: average hourly vehicle counts at three locations in Fairbanks and average hourly meteorological measurements made at a 75-ft tower in the downtown area.
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From page 70... ...
is next, followed by the inversion strengths. The R2 for the model is 0.44.
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From page 71... ...
71 en au .h 1 'e at .= o To To 'e v 'e 8 .
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From page 72... ...
A summary of estimated emissions reductions is shown in Table 2-~. The onroad mobile source emissions inventory was developed with a hybrid approach.
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From page 73... ...
Area-source emissions reductions also occurred as a result of reduced wood-burning. Reductions in nonroad mobile-source emissions are attributed to reduced aircraft emissions.
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From page 74... ...
14.40 Cold-start and initial-idle emissions 8.28 6.49 Traveling emissions 13.41 7.91 Nonroad sources 4.00 3.66 Airport ground support equipment 2.36 Aircraft, excluding ground support 1.27 equipment · Snowmobiles 0.27 Railroad operations (Locomotives) 0.04 Forklifts 0.02 0.01 Alr compressors 1.91 1.37 0.28 0.04 0.03 0.01 Area sources 1.53 0.89 Residential wood burning 1.29 0.67 Fuel oil 0.16 0.13 Natural gas - 0.01 Structural fires 0.08 0.08 Point sources 4.14 4.33 MAPCO (Williams)
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From page 75... ...
5.73 I/M Program Enhancements 1.26 I/M Increased Enforcement 0.25 Expanded Plug-Ins 0.05 Total Onroad Mobile Sources 7.29 33.6% Area Sources 0.64 41.~% Nonroad Mobile Sources 0.34 8.5% Point Sources -0.19 -4.6% Total Reductions 8.1 1 26% Source: ADEC 2001a. Vehicle-FIeet Characteristics Characterizing the onroad fleet during design conditions is critical for estimating motor-vehicle emissions.
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From page 76... ...
operated in the borough during extremely low temperatures are typically newer and better-maintained than the average summer fleet. In the winter of 2000, ADEC conducted a license-plate survey in downtown parking lots to ensure that only the vehicles normally used during the winter were included in emissions modeling for state implementation plan (SIP)
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From page 77... ...
In-Use Vehicle Controls Clean-fuels programs and I/M programs are the mainstays of nationwide in-use vehicle controls. In Fairbanks, where cold engine starts contribute substantially to the regional nonattainment emissions inventory, cold-start controls in the form of engine preheating also provide valuable emissions reductions.
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From page 78... ...
Emissions reductions were generally smaller in newer-technology vehicles (those with closed-Ioop fuel control and three-way catalysts) and larger in high-emitting and older
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From page 79... ...
and oxygenates provide little or no benefit for late-model vehicles under warmed-up running conditions, the reintroduction of oxyfuels may not provide a large emissions-reduction benefit for running exhaust emissions in Fairbanks. However, the use of oxyfuels may reduce CO emissions during cold starts in late-model vehicles when the O2-sensor is off line during the first several minutes of operation.
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From page 80... ...
Sulfur in gasoline is known to affect the efficiency of vehicle emissions-control systems adversely by poisoning the catalyst, thus decreasing pollutant conversion efficiency and potentially lengthening the time needed after vehicle ignition for the catalyst to become effective. The ~ 99 ~ Auto-OiT study concluded that reducing sulfur concentrations from 450 to 50 ppm would result in a ~ 3% decrease in CO exhaust emissions in 1990 Tier 0 technology vehicles.
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From page 81... ...
Exhaust emissions are evaluated with a two-speed idle test. Vehicles less than 2 y old and vehicles that are not driven during the winter (from November ~ to March 31)
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From page 82... ...
Methods and Data for Evaluating the I/M Program The borough would benefit from continuing evaluation of its I/M program. The evaluation should include study of the overall emissions benefits of the AM program using in-use vehicle emissions data, the level of program noncompliance, the types and effectiveness of emissions-related vehicle repairs, and the adequacy of current types of testing for identifying high-emitting vehicles.
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From page 83... ...
It is used to measure emissions from individual vehicles as they drive by a roadside sensor. Other advances that have faciTitated the collection and interpretation of remote-sensing measurements include pattern-recognition software to read vehicle license plates automatically and sensors to measure speeds and accelerations of passing vehicles.
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From page 84... ...
84 Managing Carbon Monoxide Pollution in Fairbanks, Alaska
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From page 85... ...
As described earlier, a large component of vehicle emissions during winter is attributed to cold-start operations. Therefore, effective local in-use vehicle control strategies can focus on reducing the number of winter engine cold starts or the length of time it takes for vehicles to warm up.
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From page 86... ...
A recent ordinance implemented by the borough requires employers and businesses with more than 274 parking spaces with outlets to provide power when the ambient temperature is less than 21°F (Ordinance No.
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From page 87... ...
Moderate idling times will increase idle emissions but may reduce drive-off emissions, resulting in a net decrease in emissions for the entire trip. Sparse data suggest that 5 min of idle after an engine cold start under very cold conditions may be near the optimum for reducing total CO emissions for a trip, but this optimum time varies among vehicles depending on the emissions-control system (Sierra Research ~ 9994.
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From page 88... ...
Only small CO emissions reductions are attributed to the programs in the SIP (ADEC 2001a)
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From page 89... ...
Coordinated transit program and new buses considered in SIP. 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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From page 90... ...
Could be considered to shift cold starts away from peak CO times. Not adopted.
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From page 91... ...
Aside from these numbers on past ridership, the borough has not conducted studies of transit needs in Fairbanks. Such a study would help identify whether expanding the service could result in significant emissions reductions.
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From page 92... ...
Although CO alert-day programs would not have a large effect on average annual CO emissions, they might have enough effect to help to avert an exceedance. For example, on alert days, employees could be encouraged to leave work earlier or later, shifting vehicle emissions away from the period when maximum concentrations are most likely.
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From page 93... ...
2001~. Signal timing improvement should tee a priority for implementation in downtown Fairbanks and should optimize emissions reductions rather than focusing solely on total delay.
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From page 94... ...
However, 86% of people polled listed improved vehicle starting as one of the major reasons for plugging in and only 54-56% listed improved air quality and public health as a major reason. Education and marketing have played important roles and will probably continue to do so in the borough's efforts to attain the NAAQS for CO.
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From page 95... ...
Generally, the assessment of program adoption and overall program effectiveness requires causal inference to determine the portions of the adoption and of the overall outcome that are attributable to the intervention program. For example, the borough may want to determine how much of the increase in bus ridership is attributable to having free bus service during the winter months, that is, how many of the riders would have driven a private vehicle if the incentive were not provided.
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From page 96... ...
When randomized trials are not possible due to resource limitations and other factors, such as sampling selection bias, a pre-post design is common in program evaluation.With pre-post methods, researchers assess program adoption or outcomes before and after the implementation of the intervention program and then examine the changes to assess their effect on program effectiveness. For example, I/M programs can be evaluated by comparing vehicles that have undergone emissions testing in an area with vehicles that have not or by comparing vehicle emissions in an area that has emissions testing with emissions in an area that does not.
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From page 97... ...
Therefore, CO emissions-reduction measures would probably also have a beneficial effect on the emissions of correlated pollutants, such as HC, PM~o and PM2 5, and PAHs. Mechanical Vertical Mixing The combination ofthe extremely shallow depth and strong stability ofthe atmospheric boundary layer in Fairbanks and the possibly small spatial extent of high CO concentrations provides an opportunity to consider mechanical means to disperse CO.
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From page 98... ...
SIMPLE BOX MODEL OF THE BOROUGH Various models that have been used for attainment demonstrations, research purposes, and air quality forecasting were discussed in Chapter 1.
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From page 99... ...
In addition to improving the meteorological data and emissions inventory, the borough will also have to address the limitations of widely available dispersion models under conditions of severe temperature inversions and very Tow windspeeds (Bowling 1985~. In the meantime, the committee has developed a simple box model for the borough nonattainment area to gain some insight into the roles played by emissions and meteorological variables.
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From page 100... ...
The hourly values are averaged over the five exceedance events. The Data The model inputs include average hourly values of meteorological variables and vehicle counts and average daily emissions rates.
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From page 101... ...
The hourly values are averaged over the five exceedance events. lowing the values estimated by Sierra Research in a ~ 999 CO emissions inventory.~3 Mobile sources in that inventory are estimated to be 7.0 tp]
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From page 102... ...
for the average exceedance event. outside the box are negligible)
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From page 103... ...
that is reasonable and yields a calculated CO concentration that varies with time in a way similar to the observed hourly average. Because the area of the box is constant, the variations in the volume are based on variations in the height of the mixing layer, H(t)
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From page 104... ...
and convective mixing from the rising, initially hot exhaust gas. Thus, the mixing height is rather heterogeneous over the nonattainment area, and it is difficult to determine directly from observations a single height to use in the box model.
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From page 105... ...
The highest CO emissions in the model are between 5 and 6 p.m., when vehicle traffic is maximal. However, idling emissions in the downtown area before people leave work to go home have the effect of shifting the observed emissions maximum 30-60 min earlier than would be expected on the basis of vehicle counts.
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From page 106... ...
approach used by the borough need not be identical to the one developed here; some of the modifications described above should be considered. The borough may want to use a box model in conjunction with a model that focuses on an area immediately surrounding a monitoring site, such as the probabilistic rollback models described in Chapter 1; however, the time and effort needed to develop inventories for these local modeling approaches may be better spent developing more physically comprehensive regional modeling
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From page 107... ...
SUMMARY Fairbanks presents a challenge for air quality management. It constitutes an extreme example ofthe roles oftopography and meteorology in producing air quality problems.
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From page 108... ...
Modeling CO in the borough is a serious challenge, but it can be helpful in planning and in forecasting possible exceedance days. For now, a simple box model is suggested for planning purposes; more sophisticated models either are inappropriate for the conditions or require much more extensive monitoring data.
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