Air Emissions from Manufacturing

Primary air pollutants include:

  • Sulfur oxides (SOx)
  • Nitrogen oxides (NOx)
  • Carbon monoxide (CO)
  • Volatile organic compounds (VOCs)
  • Hydrogen chloride (HCl)
  • Hydrogen fluoride (HF)
  • Hydrogen sulfide (H2S)

Secondary air pollutants include:

  • Nitrogen dioxide
  • Sulfuric acid
  • Ozone (O3)
  • Other photochemical oxidants

=  SOx – Sulfur dioxide (SO2) and sulfuric acid vapors are corrosive, colorless air pollutants emitted mainly from the combustion of fuels containing sulfur and industrial wastes containing sulfur. [1] When emitted to the atmosphere, these contaminants react due to photochemical forces to produce sulfuric acid as well as inorganic and organic sulfate compounds. A large proportion of sulfur dioxide eventually falls to the ground as acid rain or is seized by flora and fauna in the process known as disposition.

= NOx – Nitric oxides (NO) and nitrogen dioxides (NO2) account for NOx, which are created from the combustion of fuels. NO is an odorless air pollutant, and NO2 is an air pollutant with a reddish-brown color that is associated to the brown haze of photochemical smog, common to many urban areas. NO2 contributes to the formation of ground-level ozone, fine particle pollution, and is linked with a number of adverse effects on the respiratory system. [2]

=  CO – CO is a colorless, odorless and partially oxidized compound that contributes to smog formation. It’s formed from the incomplete combustion of fuel and other organic compounds due to insufficient oxygen concentration or too low of temperature, which may occur in automobiles, boilers and industrial furnaces. Other partially oxidized compounds may adhere to particulate matter or remain gaseous.

=  VOCs – VOCs are organic compounds that easily volatilize and when released to ambient air, they contribute to photochemical reactions. Organic compounds with a lack of photochemical reactivity are not considered VOCs. They are primarily emitted from the vaporization of organic compounds used as solvents in industrial operation. Such contained and fugitive emissions consist of numerous VOCs with a range of known health effects.

=  HCl, HF & H2S – HCl and HF are inorganic acidic gaseous compounds released from combustion industrial processes and well as pollution control devices. Their emitted concentrations are related to the concentrations of chloride and fluoride in the substance being combusted. H2S is a highly toxic chemical that smells like rotten eggs is gaseous form, however the human olfactory bulb quickly acclimates to this odor making it hard to detect even at high concentrations. H2S and other sulfur compounds contribute to the formation of SO2.

=  O3 – The oxidant O3 forms in the troposphere due to atmospheric reactions of NOx, VOCs and CO, known as “ground level ozone”. As levels of O3 increase, so do various partially oxidized photochemical oxidants, which are promoted by high temperatures and sunlight intensity. Ozone contributes to what we typically experience as "smog" or haze, which still occurs most frequently in the summertime, but can occur throughout the year in some southern and mountain regions. [3] Ozone is likely to reach unhealthy levels on hot sunny days in urban environments. Ozone can also be transported long distances by wind. For this reason, even rural areas can experience high ozone levels.  Ground level ozone is associated with respiratory difficulties and disease.

=  GHGs – Greenhouse Gases (GHGs) are a group of air contaminants that trap heat in our atmosphere. The most important GHGs released from human activity are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases such as hydrofluorocarbons, perfluorocarbons and sulfur hexafluorides. Different GHGs vary widely in impacts, but may be measured according to their Global Warming Potentials (GWPs).

=  HAPs – Hazardous air pollutants (HAPs) are defined in section 112 of the Clean Air Act (CAA) as any air pollutant listed in section (b), which has been amended over time but currently includes 187 pollutants and chemical groups. These chemicals are listed as HAPs due to evidence that they cause or may cause cancer or other serious health effects, or adverse environmental effects. [4] Although ambient air quality standards are not established for HAPs under the CAA to describe their legally acceptable concentrations in ambient air, they are governed by the EPA through the National Emission Standards for Hazardous Air Pollutant (NESHAP) regulations.

Typical Sustainable Supply Chain Scorecard Air Emissions Questions [5]
Scorecard Questions
  1. Does your organization employ initiatives and practical activities to reduce greenhouse gas emissions? [6]
  2. Does your organization have a program aimed at inventorying, reducing, and reporting the emissions of greenhouse gases from your operations?
  3. Does your organization have a climate strategy that identifies opportunities to reduce the organization’s emissions of greenhouse gases?
  4. Does your organization monitor and record its greenhouse gas emissions? 
  5. Are reduction targets developed for greenhouse gases and are they met?
  6. What aspects of your organization’s operations are included I the GHG emission calculation?
  7. Does your organization comply with regulations regarding emissions of greenhouse gases?
  8. Has your organization defined a baseline for its greenhouse gas emissions, which includes a definition of the business operations and activities, and the greenhouse gases that are accounted for e.g. as described in the Greenhouse Gas Protocol?
  9. What are your organization’s total direct and indirect greenhouse gas emissions by weight? [7]
  10. What are your organization’s other relevant indirect greenhouse gas emissions by weight? [8]
  11. What is your organization’s Greenhouse gas intensity? [9]
    1. (GHGs released in energy consumption for production + GHGs released in energy consumption for overhead + GHGs released by transport used for business travel + additional GHGs released from production process) / normalization factor = Tons CO2e/normalization factor
  12. By what % have your GHG emissions been reduced on a per capita basis over the last fiscal year? [10]
  13. If your organization purchased certified carbon credits in the reporting period, what % of GHG emissions were off-set? [11]
  14. Which of the following types of air emissions are generated by your organization?
    1. Volatile organic chemicals
    2. Aerosols or mists
    3. Corrosive vapors
    4. Particulate or dust
    5. Ozone depleting substances
    6. Combustion byproducts
    7. Other emissions (please specify and describe)
  15. Does your organization have a program and/or procedures for the management of airborne emissions, including monitoring, characterization, prevention, reduction and treatment?
  16. Does your organization generate regulated quantities of airborne emissions from its operations?
  17. Does your organization comply with legal requirements on emissions to air (e.g. air pollution standards and limit values)?
  18. Does your organization have the necessary permits for emissions to air?
  19. Does your organization provide information and train employees on how to manage air emissions?
  20. Are incentives in place to encourage carpooling or the use of public transportation? [12]
  21. Does your organization treat relevant pollutants before they are emitted to the atmosphere (e.g. by using filters)?
  22. Which of the following methods are used to control airborne emissions at your facility(ies)?
    1. Point of use exhaust ventilation
    2. Oxidizer
    3. Scrubber
    4. Electrostatic precipitator
    5. Carbon filtration
    6. Other methods (please describe)
    7. None (emission levels are below statutory and regulatory thresholds)
  23. Does your organization have a program comprised of resource reduction methods to reduce the amount of airborne emissions generated?
  24. What are your organization’s emissions of ozone-depleting substances by weight? [13]
  25. What are your organization’s HAPs, VOCs, NOx, SOx, and other significant air emissions by type and weight? [14]
  26. What is your organization’s intensity of pollutant releases to air? [15]
    1. Weight of releases (from production processes and, if available, overhead) to air / normalization factor = tons/normalization factor
Air Emission Indicators & Measurement

In order to answer to these scorecard requests or inquiries, a company needs to identify which indicators are going to reveal the answers to these questions and then help to identify a management strategy with established goals and targets for reduction.  Below are typical air emission operational performance indicators and methods for measuring air emissions.

Air Emission Indicators [16]
  • Quantity of each type of air emissions per year or per unit of production
  • Quantity of GHGs released per month or year
  • Amount or percentage of air emissions reduced by reduction initiatives
  • Concentration of a specific contaminant in ambient air at selected areas
  • Ambient temperature at locations within a specific range of organization’s facility
  • Frequency of photochemical smog events in a defined local area
Air Releases Intensity

It’s important for facilities to measure and monitor their releases of air pollutants, especially ones of concern like carbon monoxide, NOx, SOx, ozone, VOCs, lead and particulate matter.  Air pollution causes a variety of human health issues such as breathing problems, lung damage, cardiac conditions, and cancer. It also causes a variety of environmental issues such as acidic rain, haze and smog, and thinning the protective ozone layer of the upper atmosphere. OECD recommends their Indicator O6 to calculate your facility’s intensity of pollutant releases to air. [17] Note that this formula doesn’t account for GHGs.

Units of indicator: tons/normalization factor

Air pollutants that a facility is measuring and monitoring should already include those that are regulated or permitted, but the organization should identify other air pollutants and which ones to prioritize. The numerator should include releases from both production processes and overhead if possible.

Greenhouse Gas (GHG) Intensity

To measure all GHGs on a comparable level, each substance’s GWP was defined in relation to CO2’s GWP by a particular CO2-equivalence (CO2e) value. The GWP depends on the average atmospheric lifetime of individual GHGs. The IPCC was created by the UN Environmental Program (UNEP) and the World Meteorological Organization (WMO) to look at this global environmental issue from a scientific perspective while assessing socio-economic affects. The OECD provides their Indicator 04 for calculating your organization’s GHG intensity.

This indicator measures the GHG intensity of the facility and overhead of an organization, but not GHG releases related to the shipping of inputs, shipping of finished products, or transportation of employees. OECD calculates the GHG intensity of the product use stage and other indirect emissions (Scope 3) independently, but an organization may simply extend the margins of this formula to include them if desired. This formula accounts for all direct GHG emissions (Scope 1) as well as all indirect GHG emissions from consumption of purchased electricity, heat or steam (Scope 2). The other indirect GHGs of Scope 3 include releases from raw material extraction, the production of purchased materials and fuel sources, transportation activities related to but outside the control of the organization, and outsourced activities not included in Scope 2. An organization just starting to measure and monitor their GHG intensity should focus on their facility initially, but be sure to specify their margins if reporting it.

Air Emission Inventories, Audits & Assessments
Air emission Inventories and Assessments

Air emissions from industrial sources are one of the most difficult releases that an environmental professional may need to determine.  The U.S. Environmental Protection Agency (EPA) has published emissions factors and emission modeling guidance for calculating air emissions.  (See as an example of available guidance.)  There are several local, state and federal regulations for air emissions and many contain the method for calculating the emissions within the regulations.  Additionally, EPA has published AP-42 [18] as guidance for many process and operating scenarios at a facility.  It is highly advisable to engage with an environmental consultant with an expertise in air emissions calculations and modeling.

Greenhouse Gas Inventories

Although GHGs are released from natural sources, the concentration of their releases worldwide has exceeded far greater than historical levels due to mankind’s activities. Such activities are present throughout every industrial sector that depends on the combustion of fossil fuels, generates waste, and emits GHGs. GHGs contribute to global warming beyond natural cycles. The substances classified as GHGs include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases listed by the Intergovernmental Panel on Climate Change (IPCC). [19] Greenhouse Gas (GHG) inventories are calculated amounts of GHG emissions released to or removed from the atmosphere over a given period of time. [20] An organization can use their GHG inventories to identify emission reduction opportunities. If your organization releases greater than the regulatory threshold of CO2 equivalents annually, they are probably required by law to report their emissions to the EPA.

More likely however, a company may be asked by their customers to report their energy consumption and use data and therefore report on the equivalent GHG emissions associated with this energy.  Sustainable supply chain scorecard requests from customers for suppliers have become very popular over the last several years with a primary focus on energy and GHGs.  Identifying Scope 1, 2 and 3 GHG emissions can be a daunting task.  Many online resources are available including the Greenhouse Gas Protocol’s Corporate Standard, as developed by the World Resources Institute and the World Business Council for Sustainable Development, which is the foundation for nearly every GHG standard, inventory and program in the world. [21]

Air Emission Improvements and Implementation
Source Reduction

To prevent or stop creating pollution, such as air emissions, source reduction plays an important role.  Source reduction is any practice that:

  • Reduces the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise released into the environment (including fugitive emissions) prior to recycling, treatment, or disposal.
  • Reduces the hazards to public health and the environment associated with the release of such substances, pollutants, or contaminants.

The term "source reduction" includes:

  • Modifications to equipment or technology
  • Modifications to process or procedures
  • Modifications to process or procedures
  • Substitution of raw materials
  • Improvements in housekeeping, maintenance, training, or inventory control
Green Chemistry

Industrial air emissions are often the result of using, combining, or combusting chemicals or materials.  By using chemicals that have considered the principles of green chemistry, air emissions can potentially be reduced.  Green Chemistry “is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances .” [22]  As stated by the U.S. EPA, green chemistry,

  • Prevents pollution at the molecular level
  • Is a philosophy that applies to all areas of chemistry, not a single discipline of chemistry
  • Applies innovative scientific solutions to real-world environmental problems
  • Results in source reduction because it prevents the generation of pollution
  • Reduces the negative impacts of chemical products and processes on human health and the environment
  • Lessens and sometimes eliminates hazard from existing products and processes
  • Designs chemical products and processes to reduce their intrinsic hazards [23]

 The 12 principles of green chemistry can be considered when working with chemicals.  These principles demonstrate the breadth of the concept of green chemistry:

  1. Prevent waste: Design chemical syntheses to prevent waste. Leave no waste to treat or clean up.
  2. Maximize atom economy: Design syntheses so that the final product contains the maximum proportion of the starting materials. Waste few or no atoms.
  3. Design less hazardous chemical syntheses: Design syntheses to use and generate substances with little or no toxicity to either humans or the environment.
  4. Design safer chemicals and products: Design chemical products that are fully effective yet have little or no toxicity.
  5. Use safer solvents and reaction conditions: Avoid using solvents, separation agents, or other auxiliary chemicals. If you must use these chemicals, use safer ones.
  6. Increase energy efficiency: Run chemical reactions at room temperature and pressure whenever possible.
  7. Use renewable feedstocks: Use starting materials (also known as feedstocks) that are renewable rather than depletable. The source of renewable feedstocks is often agricultural products or the wastes of other processes; the source of depletable feedstocks is often fossil fuels (petroleum, natural gas, or coal) or mining operations.
  8. Avoid chemical derivatives: Avoid using blocking or protecting groups or any temporary modifications if possible. Derivatives use additional reagents and generate waste.
  9. Use catalysts, not stoichiometric reagents: Minimize waste by using catalytic reactions. Catalysts are effective in small amounts and can carry out a single reaction many times. They are preferable to stoichiometric reagents, which are used in excess and carry out a reaction only once.
  10. Design chemicals and products to degrade after use: Design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment.
  11. Analyze in real time to prevent pollution: Include in-process, real-time monitoring and control during syntheses to minimize or eliminate the formation of byproducts.
  12. Minimize the potential for accidents: Design chemicals and their physical forms (solid, liquid, or gas) to minimize the potential for chemical accidents including explosions, fires, and releases to the environment. [24]
Particulate Emissions

Particulate matter and dust are the most common air contaminants of fugitive emissions. They are commonly a concern in industrial environments where grinding, milling and sawing processes take place. They inhibit the efficiencies of pollution control technologies and numerous other ones. To prevent and control concentrations of particulate matter, an organization’s employees should perform dust control practices such as covering equipment, water suppression, and increasing the moisture content of material piles. Equipment used to handle materials that emit particulate matter should extract the affiliated air and treat it, such as with a baghouse or a cyclone. Operators should maintain clean equipment and a clean environment. When necessary, employees should utilize personal protective equipment such as dusk masks and respirators to avoid human health concerns.

Monitoring and Controlling Air Emissions
Air Emissions Monitoring

Organizations with a significant amount of air emissions may be required to monitor them in order to show compliance with regulatory requirements. However, organizations with less than significant emission quantities should also perform monitoring to compile performance data and get an idea of where they stand in respect to regulated quantities and competitor organizations. The National Emission Standard for Hazardous Air Pollutants (NESHAP) of the Clean Air Act (CAA) defines monitoring as “the collection and use of measurement data or other information to control the operation of a process or pollution control devices or to verify a work practice standard relative to assuming compliance with applicable requirements.”

Stationary source emissions monitoring consists of four parts; indicators, averaging time, monitoring frequency, and measurement techniques. Indicators are the measures of performance criteria, such as air pollution controls, direct emissions, surrogate emissions, opacity levels, efficiencies of emission rates, and pollutant concentrations. The time period in which the data is collected is averaged against the release of emissions in order to confirm proper compliance and verify appropriate use of pollution control strategies. The monitoring frequency is simply how many times data was collected over a given time span. Measurement techniques are the means of data collection related to indicators, and they consist of detection devices, installation specifications, inspection procedures and quality measures. Some measurement techniques include manual inspections, continuous emission monitoring systems, continuous opacity monitoring systems, and parametric monitoring systems. A continuous emission monitoring system may measure actual emission levels of a pollutant or a surrogate pollutant in place of the pollutant of concern. A continuous opacity monitoring system measures opacity, which is the proportion of visible light attenuated. Opacity is determined by the amount of light dissipated by an emission’s particulate matter. A parametric monitoring system may be continuous as well. They evaluate the system’s performance by measuring one or more key parameters that serves as a reliable indicator, such as flow rate, temperature and pressure.