Preparing for air quality initiatives

Changing air quality regulations are affecting everyone from large industrial and power plants to small manufacturers, universities, and colleges. Uncertainty has always been a component of air quality regulations, but the number of changes underway and the magnitude of these changes is overwhelming.

By Russ Price, PE, Chad Daniel, and Angela Phipps, Stanley Consultants, Iowa December 28, 2010

Congress, through the Clean Air Act (CAA) and subsequent amendments, directs the U.S. Environmental Protection Agency to protect the general public from breathing unhealthy air. The EPA frequently delegates implementation of federal rules to state regulatory agencies. Air quality regulations address pollutant emissions from mobile sources (cars and trucks), as well as stationary sources (power plants and industrial facilities).

The EPA and state agencies use several methods to ensure good air quality. One method is to establish National Ambient Air Quality Standards (NAAQS) for specific pollutants. Another is to set limits for specific air pollutants emitted by a facility through emission performance standards or permit conditions.

Explained simply, the NAAQS define the maximum concentration of a pollutant in the air that is considered acceptable to be protective of human health. NAAQS apply to the six criteria pollutants: ozone, particulate matter, nitrogen dioxide, sulfur dioxide, carbon monoxide, and lead. The EPA has started taking the steps to group greenhouse gases into this category, but that is discussed separately.

The NAAQS are the foundation of regulatory air quality programs in the United States, and in comparison to other aspects, can be considered fairly straightforward. If the air quality in an area is better than the NAAQS, it is designated as being in attainment. If the air quality in the area is worse than the NAAQS, it is designated as being in non-attainment. These determinations are made based on air quality monitors that sample the ambient air. If no monitors are nearby or considered representative, the area is designated as unclassifiable.

Areas that are designated as in attainment of the NAAQS implement regulations and programs that are focused on keeping the area in attainment. Areas that are designated as non-attainment of the NAAQS must implement programs necessary to get back into attainment. This is typically a state- or local agency-led process that is subject to review and approval by EPA.

Every five years the EPA is required to lead a thorough review of the criteria pollutants and NAAQS and to make changes to those standards that the agency finds appropriate to protect human health. This is the process through which the NAAQS for particulate matter has evolved from total suspended particulate, to particulate matter, to particulate matter less than 10 microns in aerodynamic diameter, to including a separate subcategory for particles less than 2.5 microns. Recently the EPA has proceeded with multiple revisions and reconsiderations of multiple NAAQS.

Emission standards come in several different versions. At the most basic level are the New Source Performance Standards (NSPS), which set limits on the amount of certain criteria pollutants that can be emitted by a process such as a boiler or the piping from an ethanol plant. Similar standards are developed for pollutants considered hazardous through the National Emission Standards for Hazardous Air Pollutants (NESHAP). States and local agencies may have additional performance standards in rules, and they regularly add specific standards or emission limits to air quality permits.

As noted, the NAAQS are the foundation of regulatory air quality programs in the United States. Over the years air quality in the United States has improved; the total amount of criteria air pollutant emissions has decreased,  while population and economic output has increased. But some areas are running into air quality problems. The primary reason for this is that the definition of good air quality, the NAAQS, has been routinely lowered and made more stringent over time.

Fine particulate matter

A combination of technical uncertainties, complex formation mechanisms, and the stringency of the fine particulate matter standard will result in permitting complications in addition to the need to retrofit or modify existing equipment.

Fine particulate matter (PM2.5) continues to be a NAAQS that challenges many communities. PM2.5 monitors in some rural areas can show relatively high background concentrations, on the order of 30 ug/m3. As a result, it takes very little local contribution to exceed the 24-hour standard of 35 ug/m3.

To date, the impact of the PM2.5 NAAQS has been softened by an EPA policy that allowed the use of the existing PM10 standard to be a surrogate for PM2.5. Essentially, if a project passed air quality evaluations under existing PM10 requirements, it was assumed to pass air quality evaluations under the PM2.5 requirements. This was done primarily due to the lack of quality tools and methods for assessing and evaluating the impact of PM2.5 concentrations from a facility or group of facilities. For example, as of the writing of this article, EPA has not promulgated an approved stack test method for PM2.5, which means there isn’t a formally approved method for measuring the emissions coming out of the stacks from a factory, paint booth, power plant, or university boiler.

While the technical details and methods will eventually be sorted out, the regulated community is faced with a high level of uncertainty regarding just what it will take to meet the permit application tests for PM2.5. For example, how does a permitting agency set an emissions limit, how does a regulated entity prove compliance, and how does the emission control system vendor provide a guarantee when there is no approved method of measuring what is coming out of a stack?

While the technical limitations are certainly problematic, there is a secondary aspect to PM2.5 that regulated and regulatory communities will be struggling with for some time. This secondary aspect is best summed up by the Abraham Maslow quote: “If the only tool you have is a hammer, you tend to see every problem as a nail.”

All major projects, and in some locations even minor projects, are required to complete an air quality impacts analysis as part of the preconstruction air quality permit approval process. The “hammer” in this case is local scale air dispersion modeling. Federal, state, and local regulatory agencies have long relied on local scale air dispersion modeling analyses (with very conservative operating and emission conditions) to determine whether a project that includes particulate matter emissions has an acceptable air quality impact, the least stringent tier of which is meeting the NAAQS. But PM2.5 is different. It is a combination of directly emitted fine particles, similar to PM10, and the result of secondary formation of fine particles, similar to how ozone is formed.

It is probably safe to say that in most locations the majority, and potentially the vast majority, of fine particulate matter measured at monitoring stations is the result of secondary atmospheric formation, similar to ozone. But the technical tool regulatory agencies typically use to evaluate air quality impacts is the local scale dispersion model. That tool, currently AERMOD, doesn’t do secondary atmospheric formation. In this technical vacuum regulatory agencies are rushing to put the “background concentration” plug into the dike of regulatory uncertainty. Unfortunately, this is a very conservative approach that has the significant potential to over-regulate facilities and the real potential to kill modernization and expansion efforts before they even get past the drawing board.

Until federal, state, and local agencies realize that they are implementing procedures that take care of problems that only look like nails, the transition to an effective air quality permitting process for PM2.5 is going to feel like a hammer.

Sulfur dioxide (SO2)

NAAQS have two components: the level and the form. The form of the standard defines the time period over which the standard is evaluated. Shorter time periods can have the effect of increasing the stringency of a standard by reducing the ability to average conditions over longer time periods. For sulfur dioxide, the EPA has opted to implement a standard that is based on 1-hour averages, making the new standard more difficult to comply with.

A new sulfur dioxide (SO2) NAAQS goes into effect late in 2010. The new standard is much more restrictive and can pose a challenge for compliance. Power plants as well as certain industrial processes emit SO2, and all of these sources are subject to regulation under the standard. Many utilities use a number of practices and technologies to control SO2 emissions, such as switching to lower sulfur fuels, or using lime or limestone as part of the bed materials in circulating fluidized bed boilers, wet and dry flue gas desulfurization technologies, and sorbent injection processes.

Specifically, the EPA is replacing the current 24-hour and annual standards with a new short-term standard based on the 3-year average of the 99th percentile of the yearly distribution of 1-hour daily maximum SO2 concentrations. The EPA is setting the level of this new standard at 75 ppb.

With the new 1-hour standard, EPA is also revising the ambient air quality monitoring requirements for SO2. Under the new requirements, SO2 monitors must be placed in core based statistical areas (CBSAs) based on a population weighted emissions index for the area, as follows:

  • Three monitors in CBSAs with index values of 1,000,000 or more
  • Two monitors in CBSAs with index values less than 1,000,000 but greater than 100,000
  • One monitor in all CBSAs with index values greater than 5,000.

At least 163 SO2 monitoring sites nationwide will be required under this standard. EPA estimates that 41 new monitoring sites will need to be established nationwide to meet the new monitoring requirements. Additional monitoring sites may be required for certain situations by EPA regional administrators. States must make adjustments to monitoring networks to meet the new SO2 monitoring requirements by Jan. 1, 2013. 

Based on currently available 2007-2009 air quality monitoring data from existing SO2 monitoring sites, 60 of the total 249 monitored counties violate the new 1-hour SO2 standard. EPA expects to designate areas as attainment, nonattainment, or unclassifiable by June 2012 based on more recent air quality monitoring data, most likely 2008-2010. 

The EPA also plans to use refined air dispersion modeling results where available as part of the attainment designation process. EPA expects that, in areas without currently operating SO2 monitors but with sources that might have the potential to cause or contribute to violations of the NAAQS, the identification of NAAQS violations and compliance with the 1-hour SO2 NAAQS would primarily be accomplished through refined, source-oriented air quality dispersion modeling analyses. This would be supplemented with the new, limited network of ambient air quality monitors.

The rule’s preamble proposes states initially direct the attainment demonstration modeling toward larger sources (e.g., those emitting > 100 tons per year of SO2). The preamble also suggests that states identify and in time conduct refined modeling of any other sources that may be anticipated to cause or contribute to a violation to determine compliance with the new SO2 NAAQS.

The final rule became effective Aug. 23, 2010. As a result of the new rule, any new or modified major sources are required to demonstrate compliance with the new 1-hour SO2 NAAQS as part of federal permitting projects. States may also require a similar compliance demonstration for state-level permitting projects. The final rule does not include modeling significance levels or Class I /Class II Increment Standards associated with the SO2 1-hour primary standard. Nor does the rule establish a new significant emission rate for purposes of new source review, although EPA reserves the right to do so at a later date.

Nitrogen dioxide (NO2)

Similar to SO2, the EPA also has moved to make the nitrogen dioxide (NO2) more stringent through a 1-hour standard. Startup of combustion sources, even those with state-of-the-art pollution controls, have the potential to violate this standard within air quality modeling analyses. Likewise, investments in exceptionally tall stacks for even small or intermittent sources of NO2 may become a normal occurrence as a result of this more stringent standard.

On Jan. 22, 2010, EPA strengthened the NAAQS for nitrogen dioxide by setting a new 1-hour NO2 standard at the level of 100 ppb. EPA established a new form for the 1-hour NO2 standard as the 3-year average of the 98th percentile of the annual distribution of daily maximum 1-hour average concentrations.

Currently, California is the only state that has ever had NO2 nonattainment areas, and that isn’t expected to change with this new regulation, but it does have industry on edge. The American Petroleum Institute (API), representing the oil industry, spoke out immediately against the new standard. In a release, the group claimed there is no significant evidence that the short-term NO2 standard established by the EPA administrator is necessary to protect public health. The group claims that EPA is over-regulating this air quality standard for political—not health—reasons. API said since 1990, the oil and natural gas industry has spent more than $175 billion on improving environmental performance of its products.

From a permitting perspective, the new 1-hour NO2 NAAQS is likely to cause headaches. Even facilities with the latest and greatest air pollution controls for NO2 may find the need to increase stack heights to satisfy air quality modeling reviews.

Lead (Pb)

Lead is a metal found naturally in the environment as well as in manufactured products. It can be emitted into the air in the form of particles small enough to stay suspended in the air. The EPA measures lead air pollution with monitors that capture all of those suspended particles, known as total suspended particles, or TSP.

As a result of the permanent phase-out of leaded gasoline, controls on emissions of lead compounds through the EPA’s air toxics program, and other national and state regulations, airborne lead concentrations in the United States have decreased 94% since 1980. However, more than 1,300 tons of lead are still emitted each year from about 16,000 sources, many of which emit a fraction of a ton. The highest levels of lead in air are generally found near lead smelters. Other sources of current lead emissions include:

  • Iron and steel foundries
  • Copper smelting
  • Metal mining
  • Industrial/commercial/utility boilers
  • Waste incinerators
  • Cement manufacturing
  • Glass manufacturing.

Why NAAQS revisions matter

Areas that fail to meet the NAAQS must put together a plan to bring it back into attainment with the NAAQS. The state implementation plan, or SIP, is the set of rules and actions that are designed to bring an area back into attainment. Each time the NAAQS change, the base air quality requirements change, and for nonattainment areas, even more revisions or restrictions are created. Sometimes this happens even before the regulated community has had the opportunity to finish implementing changes from the last round.

Revisions to the NAAQS become even more complicated for traditional facility permitting. In theory, the NAAQS are set based on health-related studies with no other considerations. For example, a significant basis for establishing the new 1-hour NO2 standard is associated with protecting the health of sensitive populations exposed to NO2 emissions near heavily trafficked roadways. As such, first tier of air quality monitoring for NO2 includes sites within 50 meters of major roadways.  

Whether the revised NO2 NAAQS were primarily set (or based on) health impacts of NO2 emissions associated with vehicle traffic, once final, it is almost automatically integrated into the New Source Review permitting process. Of particular concern are the air quality analyses based on air dispersion modeling that are typically required for major projects, and in some jurisdictions, even for certain minor projects. For the case of the 1-hour NO2 NAAQS, the effort to reduce the health impacts on sensitive populations near heavily trafficked roadways has the potential to have an unusual impact on facilities.

Depending on how and when states or local agencies require dispersion modeling, emergency or backup generators eventually may need to be retrofitted with stacks that are 20, 30, 40, or 50 ft higher to pass modeling muster. Emissions won’t necessarily have to change; they will just be released through a higher stack so they can disperse more and pass the conservative modeling tests. This will largely be a cost with no real environmental benefits.

Another unusual impact on facilities will be during periods of startup for boilers and combustion turbines that use state-of-the-art technology to reduce NO2 emissions. These systems take time to get the equipment, components, and emission control systems up and running safely and effectively. A combustion turbine may be able to start up in 10 to 20 minutes. Starting up a cold small boiler can take several hours, with larger or higher pressure boilers taking even longer. State-of-the art emission control systems for NO2 don’t start operating until temperatures reach approximately 700°F. These temperatures are necessary to facilitate the chemical reactions that destroy the NO2. Add that it takes time to optimize combustion, and the reduced exhaust gas temperatures and flow rates during startup conditions and modeling problems for the new 1-hour NO2 standard are going to occur unless the stack heights are increased to accommodate these startup conditions. Again, this equates to additional costs with very minimal environmental benefit, and is really not related to the strictly health-based NAAQS revision.

Interstate pollutant transport

For some pollutants, namely ozone and fine particulate matter, emissions that cross state lines and therefore state level regulatory jurisdictional boundaries can cause or interfere with the ability of an area to attain or maintain the NAAQS.

These “regional” pollutants are typically products of reactions that occur as pollutants and pollutant precursors are transported over many miles by the wind. Volatile organic compounds in combination with NOx emissions can form ozone in warm, sunny conditions. Sulfur dioxide and NOx can combine with ammonia to produce fine particulate matter such as ammonium sulfate and ammonium nitrate.

To reduce the transport of ozone and fine particulate matter, the EPA recently proposed the Transport Rule, which is designed to replace the 2005 Clean Air Interstate Rule (CAIR). Both are aimed at limiting emissions of SO2 and nitrogen oxide (NOx) from power plants in an attempt to reduce the concentration of ozone and PM2.5 in downwind non-attainment areas. The requirements of this rule are directed at power plants in roughly the eastern half of the United States.

At the core of the Transport Rule is a requirement that certain states reduce air pollutant emissions by a specific amount. The amount of reduction required at the state level is tied to the contribution that that state’s emissions have on downwind nonattainment areas. These linkages were made through regional photochemical transport models that estimate the atmospheric transport and chemical transformations of air pollutants over large geographic areas.

For example, if emissions of NOx from State A were modeled to contribute to ozone problems in State B, emissions of NOx during the ozone season were reduced to mitigate that contribution. If NOx or SO2 emissions were found to contribute to downwind PM2.5 nonattainment areas, emissions of NOx or SO2 were reduced to mitigate that contribution. Those modeled reductions were then translated to tons of emissions to be reduced.

In the proposed rule, the EPA prefers an approach that establishes state budgets and includes limited emissions trading. This approach creates four interstate trading programs. Two of the trading programs are for SO2 with the states being divided into two groups. Group 1 states must achieve greater emission reductions than group 2 states. The limited interstate emission trading allows SO2 allowances to be traded within the prescribed group. The third and fourth trading programs are for annual NOx and ozone season NOx emissions. These are not further grouped as with SO2.

Plants included in the Transport Rule are further restricted from trading by the assurance provisions proposed by EPA. These provisions effectively cap total emissions from a state within a variability range. EPA is also reviewing two alternative approaches including one that would further restrict trading to intrastate only, and another that would be a more direct command and control option.  

Even with the limited trading flexibility of EPA’s preferred option, the emission allowance markets are not likely to look or perform in the same way that the Clean Air Interstate Rule markets worked. The primary purpose will be to accommodate annual swings or variability in generation that is largely dependent on weather conditions. Other than this variability, the cost of air quality control system retrofits necessary to ensure compliance will be incurred state by state, or even company by company.

It is also clear that EPA intends to further reduce emissions within the Transport Rule framework in response to future revisions to the NAAQS for ozone and PM2.5.

Emission performance standards

Where the NAAQS are the broad foundation of air quality regulations, additional regulatory structures are designed to address specific types of equipment or processes. Examples of these include New Source Performance Standards (NSPS) and National Emission Standards for Hazardous Air Pollutants (NESHAP). These requirements generally establish numerical emission limits or work practice standards to specific types of equipment.   

The EPA recently proposed a Small Boiler MACT rule affecting hazardous air pollutant (HAP) emissions from industrial, commercial, and institutional boilers. Throughout the country, many of these units may elect to close facilities rather than invest in costly control technology or fuel switching.

Boiler MACT was promulgated by the EPA in September 2004. Then the rule was vacated June 2007 due to various lawsuits from environmental groups.


  • Draft released: April 2010
  • Published in the Federal Register: June 4, 2010
  • Comment period ended: Aug. 23, 2010
  • Promulgation: Jan. 14, 2011
  • Compliance: Jan. 14, 2014

The Boiler MACT applies to the following: major sources, either a stationary source or a group of stationary sources that emit greater than 10 tons per year of a single Hazardous Air Pollutant (HAP); or a source that emits greater than 25 tons per year of combined HAPs, coal, biomass, liquid, process gas fired boiler and fired heaters, fossil fuel fired boilers less than 25 MW, and utility boilers firing non-fossil fuel that is not a solid waste.

Greenhouse gas regulations

The new Greenhouse Gas Tailoring Rule will add emission standards for six previously unregulated gases. The EPA has yet to provide guidance to utilities on what controls would be acceptable to meet the regulation. This raises industry concern that costly or unproven technology could be forced on utilities.

In the near future, EPA will also be moving forward with a large electric generating unit MACT similar to the one for small units, and rules on coal combustion by-products. This could significantly change how utilities handle these materials, a large portion of which are currently recycled for industrial use and gypsum wallboard. There is also the looming unknown of energy and climate change legislation. It is still unclear whether federal legislation on these topics will move forward anytime soon.  

Changing air quality regulations affect almost everyone either directly or indirectly. Uncertainty has always been a component of air quality regulations, but the number of changes underway and the magnitude of these changes can be overwhelming. Sometimes hiring a professional is the best solution.

Price is a vice president and marketing group manager for Stanley Consultants’ Energy group. He is well-versed in the design of boiler systems and emission control equipment. Price has a mechanical engineering degree and an MBA from the University of Iowa, and is a licensed professional engineer in six states. Daniel is a Qualified Environmental Professional with degrees in physics and meteorology. He has a wide range of experience assisting businesses in planning for and meeting regulatory requirements. Phipps, a senior environmental scientist, is the Air Quality Services Department Manager and Office Operations Manager for Stanley Consultants’ Iowa City office. Phipps has a bachelor of science degree in environmental management from the University of Iowa.