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Guidance for Qualitative Project Level "Hot Spot" Analysis in PM-10 Nonattainment and Maintenance Areas


Examples of Qualitative Analysis Methodologies and Other Estimation Techniques

Examples of Qualitative Analysis Techniques

There are several approaches to qualitative analysis that can be used to meet the requirements of the conformity rule, the most common of which are described below. These approaches vary from a simple summary statement to more detailed analyses. The approach should be decided through consultation with all parties involved in the preparation of the analysis document, and also will be affected by the data and other resources available to the agency responsible for performing the analysis.

Information Potentially Relevant to Qualitative Analysis

As discussed, the interagency consultation process is used to determine the approach and depth of the qualitative analysis, and the outcome of that consultation should be documented. A meeting of the agencies that participate in the conformity finding including Federal, State, and local agencies should be held to discuss the best approach for any given project. It is likely that one approach may be used for one project while another approach may be more appropriate for a different project.

All analyses conducted should contain similar information regardless of the approach selected, including the project description, the factors that will influence the air quality (influence factors), and any programs that can be implemented to reduce emissions (mitigation practices) from the project.

  1. Project Description

    The qualitative analysis should begin with (or reference in the appropriate section of the NEPA document) a brief description of the project including where it is located (rural, urban, suburban) and the project’s scope (adding an interchange, widening a highway, changing signal timing, etc.).

  2. Influence Factors

    The "influence factors" are those elements that may influence the quality of the air near the project and can generally be categorized into the areas listed below. These are not the only factors that can influence the air quality near a project, however, these may be among the most critical elements. Elaboration of these influence factors is discussed in the following paragraphs.

  3. Statement of existing air quality

    Existing air quality should be included to establish the probability of air quality problems from the project. Developers and reviewers of the analysis study should be aware of the existing conditions so that they can understand the relative impact that the project is likely to have. It may be appropriate to cite published information regarding regional or local trend data on PM-10 concentrations, when such data is available and relevant to the project.

    1. Traffic associated with the project

      Traffic information should describe current volumes and expected volumes since many projects involve adding capacity to reduce congestion while other projects add new access points. Understanding whether VMT is increasing or decreasing, or how a project would change the mix of vehicles on the road will assist in judging the project’s air quality impacts. For example, increased VMT associated with a new project is an important consideration in areas with a fugitive dust problem while increased congestion may be more relevant in areas where tailpipe emissions from diesel engines are the main PM-10 source. Traffic discussions should also describe any speed changes that may result from the project since emission estimates are very sensitive to vehicle speed. The speed and volume estimating method should be included. Additionally, the "fleet" or "vehicle profile" describing the types and percentages of vehicles likely to use the project will provide important information when considering the contribution.

    2. Meteorology, seasonal and climate information for area

      Meteorology is a major influence on air pollution problems. Temperature, amount of precipitation, seasonal and other weather conditions are also influences that should be discussed. When performing a qualitative analysis for PM-10, care should be taken to separate the PM emissions related to windblown or fugitive dust from emissions due directly from the project.

    3. Location of monitoring stations

      Discussing the location of monitoring stations could also be useful since determining a project’s proximity to a monitor can help establish its influence. In addition to the project, there may be other sources of PM generated near the monitor such as a power plant, airport, or bus terminal that generate emissions not directly related to the project.

    4. Miscellaneous information

      Miscellaneous influencing factors could be whether the area has paved or unpaved shoulders, the number of unpaved roads, and whether roads are salted or sanded during winter storm events. Care should be taken to separate on-road sources of PM emissions from other sources including agricultural fields, industrial factories, and power generation plants. Also any on-road mobile source emission control programs and TCMs that will influence the emission concentrations for the area should be discussed.

  4. Mitigation Practices

    In addition to describing the project’s potential for creating an emission problem, the qualitative analysis process can provide a list of operational practices that could be implemented to mitigate or offset any PM problem from the project that may be found to occur at a later time. A table including a menu of options is included below, however, many others may be possible. The options list is divided into solutions based on the suspected cause of the pollution although there may be other causes and solutions that are available.

Options to Reduce Particulate Matter Pollution
Suspected Source of PM10 Problem Options to Reduce PM Pollution
Mitigation Measure Comments
Fugitive Dust Truck Cover Laws may require greater enforcement effort in some areas
Street cleaning program includes vacuuming and flushing
Site watering program regular program will reduce dust
Street and shoulder paving; Runoff and erosion control should reduce significant quantities of dust material
Snow and Ice Control Reduce the quantity of sand use harder material that is not prone to grinding into finer particles or additional chemical treatments
Diesel Emissions from a Bus Terminal Expansion Purchase a significant number of natural gas buses cleaner buses will reduce localized PM-10 emissions for these types of transit projects
Diesel Emissions Require PM diesel "traps" on diesel exhaust systems traps or filters can substantially reduce PM-10 emissions; programs providing financial support available
Vehicle Emissions Provide a "retrofit" program for older, higher emitting vehicles could be used on bus fleets to install newer engines or technologies known to have lower emissions

Qualitative Estimation Techniques

The following list of techniques is not exhaustive and does not imply any order of priority. The specific technique used, whether one of those below or an alternative method, should be selected and documented through the interagency consultation process or through the NEPA scoping and public involvement process.

Depending on the outcome of a qualitative analysis, some areas may choose to supplement their findings with a more technical or quantitative approach that may contribute to a better understanding of the project’s PM-10 effects. In any case, the interagency process should be used to determine the approach and method for analyzing the PM-10 effects of a project.

In general, qualitative methods can be categorized into the following approaches:

  1. Comparison to another location with similar characteristics

    This method is probably one of the easiest approaches to demonstrating that a new project will not create a PM violation. It involves reviewing similar projects constructed in the past and built in close proximity to the proposed project. Sponsors should consult with air agencies for available information from previous work which could be used to support the new project’s impact, if this work is still applicable.

  2. Findings from air quality studies

    The SIP for an area contains a tremendous amount of information on air quality conditions in nonattainment and maintenance areas. This may include monitoring data and modeling data. The SIP also contains specific information on an area’s air quality standards and goals. The SIP is an important tool to be referenced when conducting qualitative analyses for PM-10.

    It may be possible that some organization such as a State or local air agency or a university has also performed an air quality study in the local area of the proposed project. If these studies are available, they could be cited in the documentation indicating the expected air quality impacts of the proposed project. Some examples for conducting PM-10 qualitative analysis follow.

Example A: Project Which Does Not Increase VMT

A qualitative analysis was conducted for the addition of an acceleration/deceleration lane in a PM-10 nonattainment area, and re-entrained road dust is the primary source of PM-10 emissions. VMT was not expected to increase because no capacity expansion was planned for the roadway segments on either end of the project. Because VMT would not increase, and therefore fugitive PM-10 emissions from road dust are not expected to increase, the interagency consultation team concluded that there would be no impact on PM-10 emissions or concentrations, and no further analysis was needed.

Example B: Project Which Reduces Idling Emissions

The project in question involves modification of an intersection to include continuous right turn lanes in an area where idling emissions are the primary source of PM-10 emissions. While the movement improvements at the intersection would provide a slight increase in capacity, they would also reduce overall idling time at the intersection by 25 percent. The reduction in idling time would reduce idle emissions of PM-10, thus providing an overall air quality benefit. (This may also prove true for a project that converted a signalized intersection into an interchange.)

Example C: Comparison of New Project to Similar Project in the SIP

A qualitative analysis was conducted for a new freeway interchange at the edge of the urban area. This interchange would lead to VMT increases from both additional travel on the new connecting road, and from development planned for the vicinity of the interchange.

The area in question has a PM-10 maintenance plan that includes a modeled demonstration of maintenance extending out to the year 2015. The interagency consultation team decided to evaluate the new interchange by comparing it to an existing interchange that is within the PM-10 maintenance plan’s modeling domain. The team located a similar interchange that was located near the edge of the urban area, and that also had higher traffic volumes and more intensive surrounding development than that expected at the new interchange. This interchange was within a maintenance plan modeling grid that was predicted to experience PM-10 concentrations of approximately 110 micrograms per cubic meter (the PM-10 standard is 150 micrograms per cubic meter). Since this existing interchange was not predicted to experience violations of the PM-10 standard, and the new interchange would see lower traffic volumes and less development, the team concluded that the new interchange would not be likely to experience violations of the PM-10 standard.

Example D: Comparison of Project Impacts to SIP Modeling

A qualitative analysis was conducted for a major freeway interchange reconfiguration in a suburban location. The region’s travel model showed that the reconfigured interchange would experience approximately a 20 percent traffic volume increase over the existing configuration, both because of travel time savings and because the modified interchange would provide access to a new regional mall.

The interagency consultation team decided to evaluate the new interchange by calculating emission levels within the interchange’s modeling grid, and comparing them to one of the existing SIP’s modeling grids. According to the PM-10 SIP, the grid with the highest emissions levels in the metropolitan area had a modeled concentration of 149.9 micrograms per cubic meter, just below the 150 micrograms per cubic meter PM-10 standard, and had PM-10 emissions in the attainment year of 1.5 tons per day. The team reasoned that, if the grid with the reconfigured interchange were to have emissions of less than 1.5 tons per day, it could also be expected to remain in compliance with the PM-10 standard.

The team located the attainment year emissions estimate for the interchange’s grid in the PM-10 SIP document, and then added the emissions expected to result from the increased traffic volumes at the interchange as well as the new regional mall. The resulting total was 1.1 tons per day, well below the 1.5 tons per day in the high grid of the PM-10 SIP’s attainment demonstration. Thus, the team concluded that the reconfigured interchange would not experience violations of the PM10 standard.

Example E: Determination of Screening Threshold for Multiple Projects

The State DOT anticipated a large number of new interchange and other projects that would require a PM-10 qualitative analysis in the next few years. The primary source of the area’s emissions is from fugitive dust. Rather than convening the interagency consultation team for each individual project, the team agreed that it would be the most efficient use of their resources to develop a screening threshold to which individual projects could be compared. Projects below a certain threshold could proceed without further analysis, while projects that exceeded the threshold would trigger the full review process.

The State DOT retained a consultant to conduct an air quality analysis of some candidate projects. After discussing the situation with the team, it was decided that the best approach would be to determine the largest project that could be constructed without triggering a violation of the PM-10 standard. The consultant conducted an air quality modeling exercise, using typical project configurations and the highest background values typically experienced in the metropolitan area, and concluded that a project would have to generate 500,000 daily VMT within a one-square-mile area in order to cause a potential violation of the PM-10 standard. The vast majority of the projects contemplated by the State DOT fell well below this threshold, and were able to proceed without further analysis (the project documents simply referenced the study and provided project-specific traffic volumes for comparison). The few projects that were over the threshold received a project-level review by the interagency consultation team, and they were designed to include mitigation measures to reduce road dust emissions so that they fell below the emissions levels modeled in the screening study. (The mitigation measures varied by project, but they included steps to reduce soil erosion from landscaped areas, street sweeping on the approach arterials, and use of liquid deicers, which also served to protect the project bridges from corrosion.)

Example F: Comparison of the Project to Another Site Based on Monitoring Data

The project entails a modification to an interchange connecting a primary route to an interstate. The area is a nonattainment area for PM-10. It is a suburban portion of a larger metropolitan city.

A meeting was held to assess the PM-10 impacts considered likely to result from the project and included members from the MPO, FHWA, EPA, State DOT and State Air Quality Agency. This group assessed the project in several areas and concluded that PM-10 was not going to be a problem. In making this determination, several factors were considered including the existing conditions, traffic volume changes, meteorology, location and monitoring stations, and monitored concentration levels. They found the following:

Currently, PM is not a problem at this project site. Members of the interagency council reviewed information supplied by State Air Quality Agency and found the project area did not have any problems with PM-10. Information supplied to this group by the State Air Agency also noted that PM-10 emissions were shown to be decreasing at the project site.

The traffic change resulting from the project has been estimated. This estimate was provided by the State DOT and was found to be consistent with VMT increases in the metropolitan area generally where no increase in PM emissions or concentrations have been noted.

The meteorology at Project X can generally be categorized as variable, the wind varies during the day. There is often some wind which acts to disperse PM emissions at the site. There does not seem to be any noticeable dust contained in the wind. Temperature, humidity, and rainfall do not seem to influence the level of PM pollution at this site.

A monitoring station close by has not registered any violations, and through the consultation process, it was determined that VMT increases from the project would not result in a new violation.

Thus, it would appear that the concentrations of PM at this site on a daily basis are currently within the standards and that future emissions that may result from this project will be low enough that they will not introduce a PM problem.

Figure 1

Map of US denoting the counties that are (in whole or part) in nonattainment as of August 2000
Updated: 7/6/2011
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