Table of Contents
- Ambient Air
National Ambient Air Quality Standards
The National Ambient Air Quality Standards (NAAQS) are comprised of six common “criteria” pollutants which are found throughout the United States and have demonstrable negative effects on human and environmental health. These six criteria pollutants are: lead, ozone, sulfur dioxide, nitrogen oxides, carbon monoxide, and particulate matter.
The NAAQS (see the federal register here) are reviewed and revised every 5 years. However, monitoring and regulation airborne pollution have progressively decreased since this system was adopted in 1971. The NAAQS are supposed to ‘‘accurately reflect the latest scientific knowledge... of all identifiable effects on public health or welfare” from air pollution (Section 108(b)), and thus are dynamic and are expected to evolve with advances in scientific understanding of air pollution effects. “Health” and “welfare” have been interpreted through the NAAQS as a “primary” standard for human health and a “secondary” standard for the welfare of the environment, including ecological pressures. Since the intended purposes of primary and secondary standards are different (human health versus broader environmental welfare), the scientific research needed to determine primary and secondary standards are different. Thus, newly discovered information may prompt a revision of one type of standard without impacting the other. The history of the evolution of NAAQS for particulate matter (is available on the EPA's website)[http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_history.html].
In enforcement, primary standards carry more weight than secondary standards, though states need to meet both. If an area does not achieve both primary and secondary standards for a criteria pollutant, then it is considered a “nonattainment” area, and the state where that area is located needs to work with the federal government to develop a plan to improve the air quality such that it meets the NAAQS. This usually involves more permit restrictions for certain industries.
Primary standards are set to protect human health at ‘‘the maximum permissible ambient air level . . . which will protect the health of any [sensitive] group of the population” with an adequate margin of safety (Section 109 (b)(1)). This means that the airborne contaminant concentration limits are set low enough that that contaminant poses a very low risk to human health, but the concentration limits are not any lower than is absolutely necessary to ensure that low risk of people’s health being negatively impacted by the pollutant. “Risk” in this sense is expressed as the estimated number of persons who will become ill per thousand or per million people exposed. Determining what risk is acceptable is a sociological question as much as a scientific one: the standards are in essence mortality goals to reduce exposure-related death and illness in a broad population.
The NAAQS primary standards are based on scientific health effects studies, but the standards must account for uncertainties in the scientific studies that could potentially underestimate the health effects of pollutants on not only healthy adults but also vulnerable groups such as children and the elderly. Primary standards are written to protect population-wide health, but not necessarily the health of every individual.
Primary standards are set purely for health considerations and are not subject to economic analysis or feasibility studies, but the implementation of plans to achieve these standards (see State Implementation plans below) can take into account feasibility based on costs and best available control technologies (BACT). Having adequate primary standards is ultimately more economically advantageous for states because of the reduced heathcare costs of treating exposure-related illnesses.
Secondary standards aim to “protect the public welfare from any known or anticipated adverse effects associated with the presence of [the] pollutant in the ambient air’’ (Section 109 (b)(2)). Public welfare includes, but is not limited to ‘‘effects on soils, water, crops, vegetation, manmade materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being’’ (Section 302(h)). Like primary standards, secondary standards are set to ‘‘specify a level of air quality the attainment and maintenance of which ... is requisite [emphasis added] to protect the public,” meaning they are adequate to protect public welfare but are no more stringent than is absolutely necessary.
Particulate matter (PM) refers to airborne particles that can be inhaled. Please see the particulate matter wiki for much more detailed information about particulate matter.
The EPA has designated two categories of particulate matter: coarse and fine. Coarse particles have a diameter of less than 10 micrometers (μm), are called PM10, and can be inhaled part-way into the lungs. Fine particles have a diameter less than 2.5 μm, are called PM2.5, and can be inhaled deep into the lungs, into the alveoli.
It is important to note that particles up to 5 μm in diameter are considered “respirable,” meaning they can travel into the alveoli and be deposited there, with significant health consequences. Ultrafine particles, which are generally considered to be 0.1 μm or smaller, can even be absorbed directly into the bloodstream. However, there are not federal regulations concerning the ambient air concentration for respirable or ultrafine particulate matter, and they are not often monitored. There is a substantial gap between what is monitored as evidence of air quality (PM10 and PM2.5) and the air quality factors that can impact human health.
There are national ambient air quality standards for PM2.5 and PM10, and there are approximately 900 monitors throughout the United States that monitor them. See the particulate matter monitoring wiki for information about monitoring techniques. Note that 900 monitors throughout the entirety of the United States creates a fairly sparse monitoring network, so the EPA and state governments rely heavily on contaminant modeling to assess the air quality in a given area.
The standards for PM2.5 are in the form of annual average concentrations and daily concentration limits. The primary standards for PM2.5 are:
annual mean concentration of less than 12.0 μm/m3, averaged over 3 years,
24-hour concentration of less than 35 μm/m3 for the 98th percentile, averaged over 3 years. The annual mean concentration is calculated by taking the average of all samples that pass quality assurance protocols (known as “credible samples”), for each of the last three years, and then taking the average of those three annual averages. The 98th percentile of the 24-hour samples is found by listing all of the credible 24-hour samples in order of highest to lowest concentrations. The 98th percentile is the 2nd percentile down from the highest concentration, or 98th up from the lowest concentration. For a sample size of 0-50, the 98th percentile would be taken as the highest concentration; for a sample size of 51-100, the 98th percentile would be taken as the second highest concentration; for a sample size of 101-150, the 98th percentile would be taken as the third highest concentration, etc. The 98th percentile concentration for each of three years would then be averaged to assess whether or not it met the primary standard. The secondary standards for PM2.5 are: annual mean concentration of less than 15.0 μm/m3, averaged over 3 years,
24-hour concentration of less than 35 μm/m3 for the 98th percentile, averaged over 3 years. The annual concentration and the 98th percentile 24-hour concentrations are determined as described above, under the PM2.5 primary standard.
For PM10, both primary and secondary standards are a 24-hour concentration limit. For both primary and secondary standards, PM10 concentrations cannot exceed 150 μm/m3 more than once per year, averaged over three years. This means that a monitor can measure higher than 150 μm/m3 for a 24-hour sample up to three times over the course of three years.
For more information about PM2.5 and PM10 standards, here are some useful resources:
As mentioned above, if an area’s measured air does not meet the NAAQS for all criteria pollutants, it is considered “not in attainment” of those standards, and the state must work with the federal EPA to create a plan on how it will reach attainment with the standards. It is important to note that the process of determining whether or not a state is in attainment can be very slow. It requires at least three years of data, plus the time for coordination of a study, data quality assessment, and discussion of results. To officially demonstrate that a state is in nonattainment or is out of compliance with their state implementation plans can take an exhaustive amount of data. Often it is less difficult and more timely to demonstrate if a company is out of compliance with its emissions permit.
In addition to the six criteria pollutants regulated through the NAAQS, the federal government regulates emissions of 187 hazardous air pollutants (HAPs) also known as “air toxics.” Air toxics emissions limits are set to protect against “adverse environmental effects … which may reasonably be anticipated to wildlife … or significant degradation to environmental quality (EPA Air Toxics).” The list of federal air toxics can be found here. An important difference between NAAQS and HAPs regulations is that for NAAQS, the exposure is regulated (i.e. the ambient air concentrations) not specific emissions, which are dealt with in state implementation plans and permitting; for HAPs emissions are regulated but exposure is not. In some ways this makes logical sense to regulate pollution at its source rather than regulating results down the road. Simultaneously, it means that cumulative exposures to HAPs are almost certainly underestimated in areas where there are multiple emissions sources (like industrial zones, or more poignantly, residential neighborhoods amidst industrial clusters).
States are tasked with the responsibility to enforce air toxics regulations, like they are tasked with implementation of NAAQS. States also may adopt and enforce stricter regulations on the federally recognized HAPs, and states may recognize additional chemicals that are not on the federal list. At least six states have adopted respirable crystalline silica as a hazardous air pollutant. For more information about these silica regulations, please see the silica monitoring wiki.
Monitoring and Reporting
Another important difference between HAPs and NAAQS is that HAPs are not routinely monitored by government agencies. Federal and state environmental agencies do not have the physical or financial capacity to adequately measure air toxics throughout the country, and thus rely on emissions estimates and some emissions monitoring by industrial personnel. In order to apply for a new industrial permit, a proposed facility owner must calculate their estimated HAPs emissions, and they must comply with federal and state HAPs emissions limits. If the industry estimates that they will emit less than 10 tons per year of a single HAP and less than 25 tons per year cumulatively of HAPs, then by federal regulations, they do not need to monitor and report their HAPs emissions (though some states have stricter rules). For facilities that do emit more than 10 tons per years of a single HAP or 25 tons per year of combined HAPs, they must self-report their emissions to the state agency and the Toxic Release Inventory (TRI). It does not come as a surprise that the EPA has found that “recent monitoring shows that facilities typically emit more HAP emissions than they actually report (EPA NEI).”
National Air Toxics Assessment
The EPA recently conducted a National Air Toxics Assessment (NATA) based on available HAPs emissions data and pollutant modeling. EPA compiled emissions data from state agencies and industrial facility self-reported emissions data in the National Emissions Inventory, which is updated approximately every three years. The purpose of the NATA is to provide to the public very broad estimations of exposure risk to toxic air pollutants in different parts of the country, but it should not be interpreted as explicit exposure data. The NATA webpage has useful sections discussing the limitations of the assessment, mostly deriving from lack of data, and clearly states “EPA suggests that the results of this assessment be used cautiously, as the overall quality and uncertainties of the assessment will vary from location to location as well as from pollutant to pollutant.” While it is good, responsible communication for the EPA to be so clear about the limitations of their assessment, it is also a very clear indication that the public does not have access to information to adequately assess and advocate for public health.
A modeling parameter that is often overlooked by persons unfamiliar with computer modeling is the resolution of the model. The federal EPA, with access to all of the possible emissions data and any relevant ambient air data, and using the best modeling techniques, is still quite limited in their ability to assess air quality conditions on a geographic scale that would be relevant to most individuals. For example, one of the primary modeling techniques (CMAQ) used in the NATA uses a 12 km x 12 km grid resolution. When looking at the entirety of the continental United States, a 12 km x 12 km grid looks fairly high resolution. However, as an individual standing on a street corner and concerned about their air quality, realizing that the modeling (not even actual measured data) blankets a 55 square-mile area with the same air quality conditions, might highlight for the individual the uncertainty of the modeling projections. The NATA does have finer resolution than the base CMAQ modeling because it combines CMAQ with AERMOD, which has five data points within the 12 km x 12 km CMAQ grid. However, AERMOD has other drawbacks including non-conservation of mass. The combination modeling used in NATA is state-of-the-art based on available data, but its uncertainties and geographic scale limitations highlight the inability of the individual to learn relevant information about their daily exposure.
Categories of Hazardous Air Pollutants
Various national and international agencies categorize pollutants based on epidemiological information indicating whether or not they cause cancer in humans. The EPA maintains the Integrated Risk Information System (IRIS) about health effects of various chemicals in the environment, and IRIS uses the following classification scheme:
Group A: Carcinogenic to humans
Group B: Likely to be carcinogenic to humans
Group C: Suggestive evidence of carcinogenic potential
Group D: Inadequate information to assess carcinogenic potential
Group E: Not likely to be carcinogenic to humans
State agencies can adopt these categories in hazardous air pollutant classifications. The International Agency for Research on Cancer (IARC) has labeled respirable crystalline silica as “carcinogenic to humans” (see the comprehensive IARC report), and at least six U.S. states have adopted this categorization as well.
Additional accessible information about air toxics can be found at:
In addition to pollutant-specific standards such as NAAQS and the Air Toxics program, the federal EPA regulates the opacity of emissions from industries (see 40 CFR Parts 60,61,62. Opacity is the lack of transparency in the air, due to light scattering by particles. In most cases, opacity limits are set at 20% at emission sources, based on the procedure outlined in EPA Method 9 and further described in EPA’s Visual Emissions Field Manual. EPA Method 9 is a procedure to quanitatively document visual opacity, and can be the basis for enforcement action is a facility is in violation of opacity rules. Read more on the visible emissions wiki about getting certified and reporting visible emissions.
Reporting visible emissions is one of the most accessible methods for members of the public to draw enforcement activity from state and local agencies. Typically visible emissions violations result in verbal or written warnings from regulating environmental agencies, and monetary fines if emissions violations persist. For more information on the kinds of enforcement activities possible, see the EPA Enforcement Basic Information. People who have obtained certification for EPA Method 9 can submit quantitative opacity claims, but anyone can follow the procedures for EPA Method 22 to submit qualitative opacity observations. In certain states, such as Wisconsin, observations using EPA Method 22 are expressly included in state Administrative Codes to indicate compliance or lack of compliance (specifically, see Wisconsin NR 415.075(3)(c) “Emissions from all fugitive sources related to the operation of the quarry shall be controlled so that no visible emissions from these sources, as measured using Method 22 in Appendix A of 40 CFR part 60, incorporated by reference in s. NR 484.04(18), cross the facility’s property line.”)
Wisconsin State Implementation Plan
The federal EPA determines national ambient air quality standards (NAAQS), discussed above, and states have the opportunity to adopt the same standards or stricter standards. States are also tasked with determining how to implement those standards, meaning states need to determine how to regulate pollutant emissions such that resulting ambient air meets the NAAQS or stricter state ambient air standards. States also need to adopt the federal air toxics standards or develop their own stricter standards on hazardous air pollutants. State environmental agencies submit their air quality plans, known as State Implementation Plans (SIPs) to regional EPA offices, who then work with states to modify and ultimately approve the SIPs. Wisconsin’s EPA-approved SIP can be accessed here, but unfortunately half of the codes referenced for Wisconsin in the “Approved SIPs in Region 5” on the EPA website are invalid. The NR 154 codes referenced on the EPA website now contain information regarding “Best Management Practices and Cost Share Conditions” rather than the “Air Pollution Control,” that is referenced. Wisconsin’s administrative codes that contain information on Air Pollution Control are in chapters NR 400-499. Wisconsin’s NR 400-499 are also referenced on EPA Region 5’s Approved SIPs website, but it is unclear if codes and the information therein are valid or invalid. Wisconsin’s Department of Natural Resources (DNR) current Administrative Codes can be accessed here. A newly revised Wisconsin State Implementation Plan will be effective February 22, 2016.
Air Pollution Control
Wisconsin Administrative Code chapters NR 400-499 cover Air Pollution Controls. Several codes in this section are useful for communities to be familiar with to ensure that facilities the Wisconsin DNR are operating with accepted practices. Here, we highlight a couple of codes that contain particularly interesting information. Note that the code referenced here was registered in 2011, and is subject to change with the new SIP in February 2016.
Wisconsin NR 404.04 discusses ambient air quality standards, and in NR 404.04(8) and NR 404.04(9), Wisconsin formally adopts the federal NAAQS for PM10 and PM2.5, respectively.
NR 404.05 sets the “Ambient Air Increment” levels, which are the maximum increases allowed over the course of one year for concentrations of PM10, sulfur dioxide, and nitrogen dioxide. The ambient air increment levels are limits set as part of the prevention of significant deterioration (PSD) of air quality, which basically is an effort to keep areas with clean air clean -- cleaner than mandated by the NAAQS. There are three classes of air quality protection for areas, with Class I being the most protected areas, which are special areas of natural beauty such as national parks and wildernesses. Most areas are classified as Class II. Interestingly, local groups can appeal for their area to be reclassified in either direction -- petitioning to become more protected or to have fewer air quality degradation limits imposed on them. Through a long and arduous battle, the Forest County Potawatomi Reservation in northern Wisconsin successfully obtained reclassification to a Class 1 area in 2008, and regulations are mentioned in NR 405.19. Each class of area has different ambient air increment restrictions, and in NR 404.05, Wisconsin adopted the federal rules for ambient air increments.
NR 405 discusses Prevention of Significant Deterioration. NR 405.02(27) lists the emissions rate thresholds (in tons per year, tpy) for sources that are classified “significant.” Wisconsin has adopted the federal standards for these classifications, including:
25 tpy total particulate matter (no longer monitored routinely)
15 tpy PM10
10 tpy PM2.5 or 40 tpy of NOX or SO2
Classification as a significant source makes a facility or a proposed facility subject to more permit regulations and stipulations that minor sources. NR 405.04(1) provides a list of exemptions from the PSD emissions increases limits, including PM exemptions during construction of new or modified sources, and exemptions for impacts of new sources outside the U.S. that affect an American area’s air quality. This administrative code (NR 405.04(1)(d) could be a leverage point for industry interests in a state such as Wisconsin that borders a foreign nation. NR 405.07(8)(a) lists ambient air criteria pollutant increases that are small enough that the new source would be exempt from air quality modeling for that given pollutant. The exemption includes ambient air contributions up to 10 μm/m3 PM10 or 2.3 μm/m3 PM2.5. Interestingly, that increase constitutes at least 20-30% of the allowable PM10 and PM2.5 ambient concentrations, and yet, it’s contribution does not have to be appropriately monitored or measured. NR 405.15 describes Public Participation commitments of the WI DNR, which could be useful to communities to hold WI DNR accountable to the timelines and public notifications listed.
NR 406 Discusses construction permits, and NR 406.04(2) lists exemptions where no construction permits are required if several criteria are met, including emissions of no more than 3.4 pounds per hour PM10 and 2.2 pounds per hour of PM2.5. These emissions rates are just below 15 tons per year PM10 and 10 tons per year PM2.5 if continuous emissions were assumed, which is the same threshold for designating significant sources (in NR 405.02), and are the same emissions rates that allow for exemption of operating permits (NR 407.03(2). For air quality impact analyses of proposed facilities, NR 406.09 says quite vaguely that “The air quality impact of a proposed stationary source will be determined at such locations where members of the public might reasonably be exposed for time periods consistent with the ambient air quality standards for the pollutants for which analysis is carried out.”
NR 407 discusses operations permits, and NR 407.03(1) provides a long list of sources that are exempt from obtaining operations permits, including:
(v) Any quarry, mine or other facility where nonmetallic minerals are extracted that is not a ledge rock quarry or industrial sand mine.
(w) Ledge rock quarries with actual production of less than 25,000 tons per month on a rolling 12 month average, or with actual operation of less than 365 days per 5 year period.
(x) Industrial sand mines with actual production of less than 2,000 tons per month on a rolling 12 month average.
(y) Fixed sand and gravel plants and fixed crushed stone plants with capacities of 25 tons per hour or less.
(z) Portable sand and gravel plants and portable crushed stone plants with capacities of 150 tons per hour or less
These exemptions can incentivize small sand mines, or the superficial sectioning of larger operations into different mining and processing facilities.
NR 415 covers Control of Particle Emissions, and therefore is very important when dealing with frac sand mining. NR 415.04 indicates that precautions need to be taken to control fugitive dust (meaning any particle emission not from a flue or a stack), including measures such as wetting and covering materials. NR 415.04(2) necessitates that control technologies be put in place in any situation where fugitive dust contributes more than 1 μm/m3 to the annual ambient concentration or 5 μm/m3 to the 24-hour concentration, though it does not specify if those limits are for total suspended particles (TSP), PM10, or PM2.5, nor does it explicitly state methods for calculating the fugitive dust emissions contribution to ambient air concentrations. NR 415.04(2) also requires that fugitive emissions cannot exceed 20% opacity “except for 3 minutes in any hour when fugitive emissions may equal 50% opacity.” Learn more about visual emissions and visual emissions reporting on our visible emissions wiki.
NR 415.075 Discusses PM emissions limits for industrial sand mines, but NR 415.075(1)(b) outlines exempts “industrial sand mines with actual production of less than 2,000 tons per month on a rolling 12 month average,” which is 24,000 tons per year. NR 415.075(2) sets PM emissions limits throughout Wisconsin, but and while NR 415.075(2)(a) states that precautions must be taken to prevent particulate matter emissions, NR 415.075(2)(a)(7) allows for an exemption when “control measures are unnecessary due to site or meteorological conditions.” This is a broad and vague statement that could allow industry to use very minimal control techniques. NR 415.075(2)(b) limits emissions opacity to 20% at the emission source, even for fugitive emissions from haul trucks. This is potentially important in communities where trucks transport frac sand between mining, processing, and rail transit sites. NR 415.075(3) discusses control measures to keep fugitive emissions low, and NR 415.075(3)(c) necessitates that fugitive emissions from a quarry need to be controlled such that there are no visible emissions that cross the facility’s property line, and highlights EPA Method 22 as a means of evaluating visible emissions. Additionally, part(d) limits emissions from activities that are not associated with processing (such as truck traffic and storage piles) to less than 5% opacity at their source. NR 415.075(4) requires facility owners or operators to conduct ambient air monitoring, however, NR 415.075(4)(b) allows for a departure from specified monitoring programs if the applicant demonstrates that the general public will not be exposed to significant levels of particulate matter from the source, and that the source's emissions units and processes are controlled to a level which meets all applicable requirements.” This administrative code does not stipulate the evidence that would be required for that “variance” from monitoring requirements, which could be a leverage point for facilities that want to avoid conducting ambient air measurements.
NR 415.076 necessitates fugitive dust emissions control plans, but NR 415.076(1)(b) provides exception for facilities processing smaller amounts of sand or gravel, and NR 415.076(2)(e) allows for the lack of using control techniques when “site or meteorological conditions” suggest it wouldn’t be necessary.
NR 431 discusses Control of Visible Emissions. This Administrative Code has the most broad applicability of any of the codes described here since there are no facility size or facility productivity stipulations. Each facility is subject to visible emissions limitations. The general rule (NR 431.05) is that emissions cannot exceed 20% opacity. Exceptions are limited to pure water emissions and cleaning of combustion equipment, which are not relevant at industrial sand mines. NR 431.07 outlines the possibility of setting up alternative opacity limits, but that option would not be available to industrial sand mining operations because they are sources of fugitive dust. Since visible emissions limits are the most broadly applicable to facilities, and members of the public can become certified to observe and report visible emissions, it may be of interest to learn more about visual emissions and advocacy.