22.6.1 Overview
The Clean Air Act (CAA) requires the Environmental Protection Agency (EPA) set National Ambient Air Quality Standards (NAAQS) for certain pollutants[1]. The Clean Air Act (CAA) established two types of national air quality standards. Primary standards set limits to protect public health, including the health of “sensitive” populations such as asthmatics, children, and the elderly[2]. Secondary standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings[3].
22.6.2 Criteria Pollutants
Criteria pollutants are pollutants that the Environmental Protection Agency (EPA) considers common in outdoor air, harmful to human health and the environment, and that come from numerous and diverse sources[4]. The Environmental Protection Agency (EPA) has identified the following criteria pollutants:
- Carbon monoxide
- Lead
- Nitrogen dioxide
- Ozone
- Particulate matter
- Sulfur Oxides
- Volatile organic compounds
The following sections provide more information on these pollutants.
22.6.2.1 Carbon Monoxide
Carbon monoxide is generated during combustion activities (e.g., burning of hydrocarbon fuels) and higher quantities are generated when the combustion operation is not optimum (e.g., improper maintenance) and/or a low oxygen to fuel ratio is used[5]. Combustion reactions can be complex and depend upon several factors. However, carbon monoxide emissions can generally be reduced by using excess oxygen during combustion, but excess oxygen can create more nitrogen oxides, another criteria pollutant[6].
22.6.2.2 Lead
Lead emissions are generated during lead material operations, other metal and ore operations and some fuel combustion (e.g., coal, fuel oil)[7].
22.6.2.3 Nitrogen Dioxide
Nitrogen dioxide is used as an indicator for a group of nitrogen oxides (NOx pronounced “knocks”) that include nitrous acid and nitric acid[8]. Nitrogen oxides (NOx) can contribute to acid rain and react with volatile organic compounds (VOC) to form ozone in the lower atmosphere[9].
Nitrogen dioxide (NO2) is generated during combustion activities when nitrogen reacts with oxygen. One source of the nitrogen can be from elemental nitrogen in the fuel, called fuel NOx, which is generated from burning oils and coals[10].
Another source of nitrogen dioxide (NO2) formation is from nitrogen in the air (i.e., roughly 79% of air is nitrogen) reacting with oxygen, called thermal NOx, which occurs at the high temperatures associated with combustion reactions[11]. Higher temperatures and oxygen concentrations can increase the thermal NOx formation[12].
The third nitrogen dioxide (NO2) formation, prompt NOx, occurs when nitrogen in the air reacts with free radicals from the combustion process which are then oxidized to nitrogen oxides (NOx)[13].
22.6.2.4 Ozone
Ozone results from atmospheric reactions between nitrogen oxides (NOx) and volatile organic compounds (VOC)[14]. The air permit requirements do not regulate ozone emissions, but rather regulate the emissions of the precursors (i.e., nitrogen dioxide (NO2) and volatile organic compounds (VOC)). Therefore, I am not aware of air permit regulations on ozone generators, which are used for odor removal and disinfection. However, some state, local environmental regulatory agencies and/or municipalities might have air permit regulations and ozone generators might be regulated due to employee or consumer safety reasons.
Some confusion may be encountered related to ozone, since ozone depleting substance are also regulated by the EPA: ground-level ozone is hazardous to human health and the environment, but the ozone layer, located in the stratosphere, absorbs ultraviolet light, which is also harmful[15].
22.6.2.5 Particulate Matter (PM)
Particulate matter (PM) are solid particles (e.g., dust) in the air. Although dust may seem like a simple concept, the Environmental Protection Agency (EPA) regulates different sizes of particulate matter (PM)[16]. Also, most of the particulate matter (PM) is formed from chemical reactions in the atmosphere[17] and not necessarily from visibly dusty operations.
22.6.2.5.1 Total Suspended Particulates
The original ambient air quality standards regulated total suspended particulates (TSP)[18]. As the name implies, total suspended particulates (TSP) include all of the particulate matter (PM) in the air and includes the next two categories of particulate matter. Although the Environmental Protection Agency (EPA) no longer has a total suspended particulate (TSP) National Ambient Air Quality Standards (NAAQS), it is still a regulated pollutant.
22.6.2.5.2 PM10
Although some regulations still apply to or refer to the total suspended particulates (TSP) standard, in 1987, the National Ambient Air Quality Standards (NAAQS) standard changed to focus on particles that could penetrate into the lungs[19]. Specifically, the Environmental Protection Agency (EPA) identified particulate matter with a nominal aerodynamic diameter of 10 microns (e.g., 0.0003937 inches) or less (PM10).
22.6.2.5.3 PM2.5
In 1997, the Environmental Protection Agency (EPA) developed a National Ambient Air Quality Standards (NAAQS) for particulate matter with a nominal aerodynamic diameter of 2.5 microns (0.00009843 inches) or less (PM2.5), which are particles that can reportedly penetrate deeper into the respiratory system[20]. PM2.5 generation is thought to form in atmospheric chemical reactions between sulfur and nitrogen compounds[21]. Therefore, PM2.5 generation will occur from combustion processes and limited quantities are likely generated from mechanical processes, but the emissions data is not always available.
22.6.2.5.4 Speciation
If you only have TSP or PM10 emission factors, you can estimate the emissions of smaller particles, which is referred to as speciation. Generally, you can assume that combustion emissions are comprised of PM10 or smaller particles. You can also use some of the Environmental Protection Agency’s AP-42: Compilation of Air Pollutant Emission Factors (AP-42) appendices for additional information. AP-42 Appendix B-1, “Particle Size Distribution Data and Sized Emission Factors For Selected Sources”, provides particles sizes for a number of specific processes. AP-42 Appendix B.2, “Generalized Particle Size Distributions”, provides particle size distribution for general processes. The California Air Resources Board has the California Emission Inventory Development and Reporting System (CEIDARS) PM2.5 database[22] that may also be a resource for speciating particulate matter.
22.6.2.5.5 Filterable Versus Condensable
Another differentiation you might see for particulate matter is filterable and condensable. Filterable particulate matter can be captured on a filter since it is composed of solid or liquid particles[23]. Condensable particulate matter is generated in gaseous form, which can flow through a filter, but can be condensed into a solid upon cooling[24].
22.6.2.6 Sulfur Oxides
Sulfur oxides are generated during the combustion of sulfur-containing fuels (e.g., coal, fuel oil, diesel, etc.)[25]. The sulfur content of the fuel dictates the sulfur dioxide emissions during the combustion process[26].
22.6.2.7 Volatile Organic Compounds
Volatile organic compounds (VOC) are carbon-containing chemicals that participate in atmospheric photochemical reactions (i.e., react to form ozone)[27]. The Environmental Protection Agency (EPA) has not established a list of volatile organic compounds (VOC) but has procedures and methods (Environmental Protection Agency (EPA) Method 25 Determination Of The Volatile Organic Concentration Of Waste Samples) for analyzing materials to determine their volatile organic compounds (VOC) content[28].
Some carbon-containing chemicals that might volatilize are exempt from consideration as VOC since they have negligible photoreactivity[29]. The Environmental Protection Agency (EPA) has provided a list of some of these compounds, which include carbon monoxide, carbon dioxide and carbonic acid[30].
22.6.3 Hazardous Air Pollutants
The Environmental Protection Agency (EPA) has identified 187 chemicals as hazardous air pollutants (HAP) due to their toxicity and prevalence[31]. The Environmental Protection Agency (EPA) has not set National Ambient Air Quality Standards (NAAQS) for hazardous air pollutants (HAP), but some states have set ambient air quality standards for hazardous air pollutants (HAP) and may require air modeling.
22.6.4 Impact on Facilities
During some air construction and operating permit application processes, a company may have to demonstrate compliance with the National Ambient Air Quality Standards (NAAQS) using computer models that mimic the emissions from the facility. The Environmental Protection Agency (EPA) has lowered the National Ambient Air Quality Standards (NAAQS) for several criteria pollutants, making it more difficult to meet the standard when modeling. If a company cannot demonstrate compliance with the National Ambient Air Quality Standards (NAAQS) during modeling, they may have to install additional control devices (e.g., baghouses, cyclones, enclosures, mineral oil application, etc.) or make other modifications to the project design.
22.6.5 References
[1] “Reviewing National Ambient Air Quality Standards (NAAQS): Scientific and Technical Information” (https://www.epa.gov/naaqs) accessed September 11, 2022
[2] Ibid
[3] Ibid
[4] “Reviewing National Ambient Air Quality Standards (NAAQS): Scientific and Technical Information, EPA website (https://www.epa.gov/naaqs), accessed January 8, 2018
[5] “Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources, AP-42″ Fifth Edition, by the U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Office of Air and Radiation, Section 1.3.3.4 Carbon Monoxide Emissions, May 2010
[6] “Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources, AP-42″ Fifth Edition, by the U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Office of Air and Radiation, Section 1.3.3.3 Nitrogen Oxide Emissions, May 2010.
[7] “Basic Information About Lead in the Atmosphere” Environmental Protection Agency website (Basic Information about Lead Air Pollution | US EPA) accessed December 30, 2022.
[8] “Basic Information About NO2” U.S. Environmental Protection Agency website (https://www.epa.gov/no2-pollution/basic-information-about-no2#What is NO2) accessed August 20, 2018.
[9] Ibid
[10] “NOx” Wikipedia webpage (https://en.wikipedia.org/wiki/NOx) accessed August 20, 2018
[11] “How is NOx Formed” Boiler Technologies by Energy Solutions Center ESC website (http://cleanboiler.org/workshop/how-is-nox-formed/#:~:text=Thermal%20NOx%20is%20formed%20when%20nitrogen%20and%20oxygen,formation%20generally%20increases%20significantly%20above%202%2C800%C2%B0F%20flame%20temperature.) accessed December 30, 2022.
[12] “Basic Information About NO2” U.S. Environmental Protection Agency website (https://www.epa.gov/no2-pollution/basic-information-about-no2#What is NO2) accessed August 20, 2018.
[13] “NOx” Wikipedia webpage (https://en.wikipedia.org/wiki/NOx) accessed August 20, 2018
[14] “hat Are The Causes And Effects Of Ozone Air Pollution?” World Atlas Website (https://www.worldatlas.com/articles/what-are-the-causes-and-effects-of-ozone-air- pollution.html#:~:text=Causes%20Of%20Ozone%20Air%20Pollution%20.%20The%20formation,unhealthy%20ozone.%20Exposure%20occurs%20both%20indoors%20and%20outdoors.) accessed September 11, 2022
[15] “Basic Ozone Layer Science” webpage (https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science), accessed December 23, 2020.
[16] “What Is PM, and How Does It Get Into the Air?” EPA webpage (https://www.epa.gov/pm-pollution/particulate-matter-pm-basics#PM ), accessed September 10, 2022.
[17] “Particulate Matter (PM) Pollution” EPA webpage (https://www.epa.gov/pm-pollution) access September 10, 2022.
[18] “Revisions to the National Ambient Air Quality Standards for Particulate Matter” Federal Register Volume 52, Number 126, July 1, 1987, Page 24635.
[19] Ibid, page 24639.
[20] “National Ambient Air Quality Standards for Particulate Matter”, Federal Register, Volume 62, Number 138, July 18, 1997, page 38662.
[21] “Particulate Matter (PM) Basics” Environmental Protection Agency website (https://www.epa.gov/pm-pollution/particulate-matter-pm-basics#PM), accessed December 23, 2020
[22] “CEIDARS 2.5 Database Structure, California Air Resources Board website (Emission Inventory; CEIDARS Database Structure (ca.gov)) last reviewed March 13, 2013.
[23] “Flavors of Particulate Matter” by Robynn Andracsek, P.E. Burns and McDonnell, Power Engineering website (https://www.power-eng.com/news/flavors-of-particulate-matter/#:~:text=Filterable%20emissions%20exit%20a%20stack%20in%20either%20solid,therefore%2C%20they%20cannot%20be%20caught%20by%20a%20filter.) accessed September 10, 2022.
[24] Ibid
[25] “Sulfur Dioxide (SO2) Pollution” Environmental Protection Agency website (https://www.epa.gov/so2-pollution/sulfur-dioxide-basics#what%20is%20so2), accessed December 30, 2022.
[26] “Sulfur Dioxide (SO2) Pollution” Environmental Protection Agency website (https://www.epa.gov/so2-pollution/sulfur-dioxide-basics#what%20is%20so2), accessed December 30, 2022.
[27] “Technical Overview of Volatile Organic Compounds” Environmental Protection Agency website (https://www.epa.gov/indoor-air-quality-iaq/technical-overview-volatile-organic-compounds#definition), accessed December 30, 2022
[28] “Referred Air Method 25D: Determination of the Volatile Organic Concentration of Waste Samples” Environmental protection Agency website (https://www.epa.gov/hw-sw846/referred-air-method-25d-determination-volatile-organic-concentration-waste-samples#:~:text=Referred%20Air%20Method%2025D%3A%20Determination%20of%20the%20Volatile,developed%20and%20promulgated%20by%20EPA%27s%20Emissions%20Measurement%20Center.) accessed September 10, 2022.
[29] 40 Code of Federal Regulations 51.100(s) Definition for Volatile Organic Compounds
[30] Ibid
[31] “Initial List of Hazardous Air Pollutants with Modification“ Environmental Protection Agency website (https://www.epa.gov/haps/initial-list-hazardous-air-pollutants-modifications) accessed December 30, 2022.
I am always open to comments and suggestions. You can contact me using the form below.