1660320351033 Strategiespreparenaaqsrevisions2

5 strategies to prepare for NAAQS revisions

Sept. 25, 2012
Upfront planning and strategizing can help achieve compliance within reasonable time and cost.

In brief:

  • The Clean Air Act sets NAAQS for six principal pollutants considered harmful to public health.
  • At the recommendation of the Clean Air Scientific Advisory Committee, EPA has recently promulgated regulations that lower allowable concentrations for these pollutants.
  • For those plant owners and operators who operate fuel burning equipment such as large boilers or furnaces or processes that generate pollutants, take note that these changes.

Many plant owners and operators are bracing for the biggest changes to the National Ambient Air Quality Standards (NAAQS) since the Clean Air Act was first enacted in 1972. Those who are unprepared could face significant permitting challenges.

The Clean Air Act sets NAAQS for six principal pollutants considered harmful to public health. These include carbon monoxide, lead, nitrogen dioxide (NO2), ozone, particulate matter less than 10 microns and 2.5 microns (PM10 and PM2.5), and sulfur dioxide (SO2). At the recommendation of the Clean Air Scientific Advisory Committee, EPA has recently promulgated regulations that lower allowable concentrations for these pollutants. The installation of new equipment or significant modifications to existing equipment requires a demonstration of compliance with the more stringent NAAQS as part of an air permit application prior to constructing or modifying these emission sources.

For those plant owners and operators who operate fuel burning equipment such as large boilers or furnaces or processes that generate these pollutants, take note that these changes, particularly those to the NO2 and SO2 standards, have tremendous permitting implications. However, a little upfront planning and a comprehensive look at five basic strategies can help achieve compliance within reasonable time and cost.

One-hour standard adjustments

EPA first adopted the NAAQS for criteria pollutants in the early 1970s, setting both a primary standard to protect health and a secondary standard to protect the public welfare. For NO2 , the standard was set at 0.053 parts per million (53 ppb), averaged annually. In 2010, EPA established a new one-hour NO2 standard at a level of 100 ppb and retained the annual average NO2 standard of 53 ppb.

Similarly, EPA first set the NAAQS primary 24-hour standard for SO2 at 140 ppb and an annual average standard at 30 ppb to protect public health. EPA also set a three-hour average secondary standard at 0.5 ppm to protect public welfare. In 2010, EPA revised the primary SO2 standard by establishing a new one-hour standard at a level of 75 ppb and revoked the two existing primary standards (the 24-hour and annual).

For owner/operators seeking to obtain air construction permits for new or modified equipment, the shorter, one-hour averaging period can be challenging, as there are peaks and fluctuations in emissions during equipment startup and operation that could previously be averaged over a year. Likewise, background ambient one-hour concentrations that must be added to concentrations from the facility’s emissions for the compliance demonstration could have peaks, depending on the location of the facility and the background monitoring data used. Thus, where compliance could previously be demonstrated by averaging concentrations over the period of a year, the one-hour standards must account for peaks associated with both equipment emissions and ambient background emissions.

Assessing attainment status

When a region within a state is designated as “nonattainment” with a NAAQS, the state regulatory authority must prepare a state implementation plan (SIP) that lays out the means for bringing the area into compliance. The repercussions of nonattainment for a state or region are great.


One year from the date of a nonattainment designation, federally funded highway and transit projects will not be allowed to proceed unless the state demonstrates there will be no increase in emissions associated with the projects. State authorities usually target manufacturing facilities to ratchet down emissions, and owners/operators of emission sources will often be subject to more restrictive permitting requirements. In order to obtain an air permit, new and upgraded facilities that are classified as “major stationary sources” located in or near nonattainment areas are required to install lowest achievable emission reduction (LAER) for equipment/processes. LAER is the most effective emissions reduction controls without consideration of cost. In addition, mandatory emissions offsetting could be required. Prior to permitting the construction of new facilities, a state must offset any emissions increases by achieving reductions at existing facilities.

States are currently making changes to the network of ambient monitoring equipment and collecting ambient data to determine the attainment status with respect to the new standards. Since the one-hour standards are a new requirement, there is uncertainty as to the compliance status of a region with the NO2 and SO2 NAAQS.

5 to survive

To protect future growth potential of a business in light of the new standards, it is important to analyze permit strategies well in advance. The solutions are based on site-specific conditions, such as opportunities for fuel modifications and equipment modifications to reduce energy consumption, and air dispersion modeling and sensitivity analyses to determine ways to reduce ambient concentrations at the facility’s property boundary. The following details five potential strategies to consider.

1. Cost/no cost options

An emission reduction option that may not have been feasible in the past might be feasible in light of the new NAAQS. In a nonattainment area, LAER requirements, which are the most stringent emission limitations achieved in practice for such class or category of source without consideration for economic impact, could be required. An investment to keep facility-wide emissions below the “major source” thresholds under the Federal Title V or New Source Review program could be more cost-effective if it results in avoiding LAER for the new emission source being installed, among other requirements associated with the rigorous federal permitting scheme. Examples of such investments may include the use of low-NOx burners or installation of a control device on another process that reduces overall facility-wide emissions for the pollutants of concern.

2. Energy efficiency improvements

Energy efficiency improvements can be a benefit on several fronts. In one example, a facility redesigned fan blades to improve blade pitch and improved the fan efficiency. The new fan design resulted in a slight increase in manufacturing cost. However, this cost was offset by lower energy use that reduced emissions below emission thresholds of concern. The initial focus was on reducing criteria pollutants, but as a bonus, the facility reduced its carbon footprint. 

3. Fuel modifications

If a facility is currently using coal or fuel oil for boilers or cogeneration units, an investment to switch to a cleaner burning fuel may become attractive on several fronts. The use of a cleaner burning fuel could allow a facility to avoid multiple new regulatory requirements, including the National Emission Standards for Hazardous Air Pollutants that is currently being promulgated for boilers burning oil or coal; the greenhouse gas tailoring rule that requires best available control technology for carbon dioxide and other global warming gases; and a major source modification and the ensuing LAER requirements altogether. Note that for new fuel-burning equipment, if an area is designated nonattainment and the source is subject to LAER, the use of a cleaner burning fuel such as natural gas or propane or the use of a low NOx burner will likely be a mandatory requirement.

4. Air dispersion modeling considerations

Food processing facility’s NAAQS challenge and solution

A food processing facility was considering a major expansion that would increase production by approximately 30%. The facility operated three boilers, one large coal-fired boiler that was used as the primary heat source and two smaller natural gas-fired boilers that provided back-up heat to ovens throughout the facility. Since the boilers were constructed 20 years ago, the permit was issued without a demonstration of the new NAAQS. Preliminary modeling was conducted that highlighted two challenges: background ambient data was relatively high because the facility was located in an urban area and the property boundary was within 150 ft of the stacks, offering very little buffer to dilute concentrations beyond the fenceline.

To avoid the construction of costly air pollution control equipment, the plant looked at two options. The first option was to increase the use of the existing boilers at a higher capacity. With this option, the facility could retrofit the coal-fired boiler to burn natural gas and apply for a PAL permit that sets permitted emission limits at a higher level than what is needed for emissions associated with burning natural gas. The boiler retrofit modification results in a net decrease in emissions, thereby avoiding modeling and rigorous permit submittals. If modeling was required, both SO2 and NO2 are both significantly lower when burning natural gas, which would result in a demonstration of compliance with the NAAQS.

The second option was to construct direct-fired ovens instead of relying on the boilers for heat. Each of the ovens have their own associated stack, and pollutant concentrations are diluted by virtue of lower emission rates from several stacks across the roof plain and a greater distance to the property boundary.

In this case, the latter option was chosen as the most feasible, highlighting the importance of pre-planning and preliminary air dispersion modeling.

Well in advance of a project, consider conducting preliminary air dispersion modeling to assess the expected concentrations of pollutants beyond the property boundary and assess the compliance status with the NAAQS. If model compliance is not initially demonstrated for peak or desired facility operations, a modeling sensitivity analysis could be conducted that assesses what effect a change in certain parameters has on off-site concentrations. For example, the sensitivity model runs would determine the effect of raising the stack height or moving equipment further from the property boundary, for better dilution and minimizing downwash influences from nearby building structures, on non-compliant receptor points. One of the benefits to conducting a sensitivity analysis is the determination of parameters that most effectively reduce off-site concentrations and allow for planning of the most feasible plant design or operations strategies.

Further, the accuracy of model input parameters becomes more critical when a facility is faced with demonstrating compliance for a standard that has become more stringent. While use of worst-case data, such as using published emission factors for estimating process emissions or applying readily available high ambient background concentration data, may have allowed a facility to show compliance from an historical perspective, the new tighter standards may not allow much room for taking shortcuts. With these tighter standards, it is important to assess whether the ambient concentration of background air quality data, from agency-operated monitoring stations, is representative of air quality in the vicinity of your facility. Most agencies publish background data from a regional network of monitors. Sometimes these monitors are many miles away, often located in an urban area. Often the monitors are cited as part of a compliance demonstration for monitoring maximum concentrations from a particular facility and therefore are not representative of background air quality levels. If your plant is in a rural area and the nearest monitor, say 15 miles from the facility, is in an urban area, this background data may not be appropriate to use as part of the analysis. Note that most regulatory agencies allow the use of monitoring data from another location even out of state if the permittee can provide good supporting information that the alternate location is more representative of ambient air near the facility.

The emission rates of the process/equipment are another critical input parameter for the model. Typically, direct source measurements such as stack testing can provide more accurate information than other estimation techniques, such as the use of EPA’s published emission factors for given processes. If preliminary modeling does not demonstrate compliance, consider the source of the emission information provided and the feasibility of equipment-manufacturer data or site-specific stack testing.

5. Plant-wide applicability limit (PAL)

For those facilities that are currently “major sources”, a PAL permit is an option that can allow significant flexibility. This provision of the Clean Air Act is underutilized by industry. EPA allows a plant-wide emission limit for one or multiple pollutants, and the limit is set based on the highest 24-month average emissions reported over the past five years plus potential emissions of processes installed after a chosen baseline period. The limit is set for rolling 12-month emission caps. As long as a facility stays under the annual PAL for the given pollutant, new installations or modifications can be made without triggering a permit review or NAAQS compliance demonstration.

A PAL permit is often most feasible if historic emissions from a plant are high and then become lower for various reasons such as reduced manufacturing or use of a cleaner burning fuel. As an example, if a facility holds a Title V air permit and retrofits its coal-fired boilers to burn natural gas, a PAL permit would cap emissions for the entire plant at levels that represent the highest pollutant levels reported, plus the potential emissions associated with processes installed after that date.

Continued deliberation

Christine K. Brenk, CHMM, is project manager at the Charlotte, North Carolina, office of Kleinfelder (www.kleinfelder.com), an industrial consulting firm. She can be reached at (704) 598-1049, ext. 451, or [email protected].

The implications of the tighter NAAQS for facilities planning to modify or construct emission sources can be tremendous, and plant owners/operators should plan for the time required to assess the facility’s compliance status and options to overcome permitting hurdles. In addition, consider that the one-hour NAAQS standard is new territory for the state agencies, and EPA guidance is still evolving. As a result, there could be much deliberation between the local regulatory authority and EPA review of applications after they are received.

Finally, if there are permit modifications anticipated for a facility within the next five years, it is important to educate plant management and other site decision makers regarding the potential repercussions of the tightened NAAQS so that the required pre-planning allows time to evaluate and implement the most feasible means for achieving compliance.

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