Ambient Air Monitoring: Where Are We Headed?

We have seen a flurry of activity lately from the United States Environmental Protection Agency (U.S. EPA), including several rules that have ambient air monitoring implications. U.S. EPA recently lowered the annual National Ambient Air Quality Standard (NAAQS) for particulate matter of diameter 2.5 microns or less (PM_2.5) and has issued (or is about to issue) amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) that regulate coke ovens and the chemical, polymers and resins, and iron and steel manufacturing industries.

These amendments are a result of Clean Air Act (CAA) mandated periodic regulatory reviews and a recent court decision that determined U.S. EPA must address previously unregulated hazardous air pollutants (HAPs) and HAP emissions sources. As part of the NESHAP rule amendments, certain industries will be required to measure fugitive emissions at the fenceline (where fenceline is equivalent to the perimeter of a facility). U.S. EPA is also working on revisions to the NESHAP for secondary lead smelters and other industries and is considering incorporating fenceline monitoring into additional rules.

With respect to these updates, the next few sections present a summary of fenceline monitoring methods, action levels, and data reporting. The conclusion of this article will explore other drivers for ambient monitoring that we are starting to see. For example, whether to install your own ambient monitoring equipment is a question you should consider as part of your strategy for living under the lower PM_2.5 NAAQS.

Fenceline Monitoring Requirements

U.S. EPA required fenceline monitoring in a NESHAP for the first time as part of the Refinery Sector Rulemaking in 2015. Recently, it has added it to rules for three more industries.

Synthetic Organic Chemical Manufacturing Industry

If the Hazardous Organic NESHAP (HON) and Polymers and Resins I (P&R I) rules are finalized as proposed, fenceline monitoring will be required for subject facilities where the facility or ‘site’ uses, produces, stores, or emits the following six HAPs: benzene, 1,3-butadiene, chloroprene, ethylene dichloride, ethylene oxide, and vinyl chloride in any quantity. Four of the six HAPs (benzene, 1,3-butadiene, chloroprene, and ethylene dichloride) will be collected using passive samplers, over a 14-day sampling period, every two weeks following U.S. EPA Method 325 A and analyzed via U.S. EPA Method 325 B.

For the two remaining HAPs (ethylene oxide and vinyl chloride) sampling and analysis will follow a newly proposed method (U.S. EPA Method 327) associated with canister sampling. Canister samples will be collected over a 24-hour sampling period once every five days. The minimum number of proposed sampling locations is twelve for the passive samplers and eight for the canister samplers; however, the number could increase based on the size and shape of your facility and proximity to known sources.

Iron and Steel

For Iron and Steel manufacturers, the U.S. EPA is requiring facilities to measure chromium (Cr) on the one-in-six-day U.S. EPA sampling schedule at four ambient air monitors, regardless of facility size, over a 24-hour sampling period. U.S. EPA has not specified a designated sampling or analysis method in the rule; though, historical sampling for metals has followed 40 CFR Part 50, Appendix B – Reference Method for the Determination of Suspended Particulate Matter (PM) in the Atmosphere (High-Volume Method) for collecting total suspended particulate (TSP) matter, with a metals analysis by means of an Inorganic (IO) Compendium Method for the determination of metals in ambient PM samples.

Coke Ovens

U.S. EPA proposed fenceline monitoring for benzene (as a surrogate for coke oven emissions), with sampling and analysis according to U.S. EPA Method 325A/B. The proposed sampling duration is the same as for the SOCMI Industry: a 14-day sampling period every two weeks using passive samplers. The proposed rule requires deploying a minimum of 12 passive samplers at locations circling the coke oven facility perimeter according to EPA Method 325A.

Secondary Lead Smelters

In November 2023, U.S. EPA issued an Information Collection Request (ICR) to secondary lead smelting facilities. As part of this request, facilities are required to monitor for lead (Pb) and arsenic (As) utilizing a minimum of four equally spaced sampling locations along the fenceline to determine upwind and downwind concentrations. A total of thirty samples are required, each over a 24-hour sampling period every six days. Sampling is to follow Title 40 CFR Part 50, Appendix B (as mentioned for the Iron and Steel facilities) with Pb and As analysis following U.S. EPA IO Compendium Method, IO-3.5. U.S. EPA will review the results of the ICR and determine whether fenceline monitoring should be added to the secondary lead smelting NESHAP as part of gap filling to address emissions of all HAPs from all sources.

Action Levels

When fenceline monitoring is included in its rules, U.S. EPA specifies 12-month annual rolling action levels in micrograms per cubic meter (µg/m³) of air. The action level is intended to reflect onsite fugitive emissions sources only and exclude background concentrations. To account for background, each facility determines a delta concentration (Δc), calculated as the lowest sample value subtracted from the highest sample value for each sampling period. This approach is intended to subtract out any estimated contribution from background emissions that do not originate from the facility. If the rolling annual average exceeds the concentration action level, a root cause analysis and corrective action are required to address the exceedance. Specific action levels vary by pollutant and rule.

Data Reporting

If the rules are finalized as proposed, Chemical and Coke Oven facilities will be required to calculate a rolling annual average within 30 days of completion of each sampling episode and report the data for each monitor within 45 days of the end of each quarterly period through U.S. EPA’s Compliance and Emissions Data Reporting Interface (CEDRI), which is located on EPA’s Central Data Exchange (CDX). Iron and Steel facilities are required to report a 12-month rolling average to CEDRI as well. Data submitted to CEDRI will be available to the public.

All submittals will include individual sample results from each sampler or monitor, coordinates of all sampler or monitor locations, 12-month rolling average concentration values, and notes for each value (e.g., background corrections used, if the value was under a lab method detection limit (MDL), or if an outlier was removed from the data set). For Secondary Lead Smelters, sampling data are being submitted to EPA using the Electronic Reporting Tool (ERT).

What Else is on the Horizon That Could Include Ambient Monitoring?

While fenceline monitoring for HAPs is key for the industries noted above, other items that could impact ambient monitoring include:

• The next round of technology reviews for NESHAP. U.S. EPA may find fenceline monitoring is necessary during its next technology review for NESHAP with facilities that emit the same HAPs as the facilities in source categories already required to perform fenceline monitoring, especially if there is a concern about fugitive emissions sources and remaining risk.
• The lower annual PM₅ NAAQS. Facilities that emit PM_2.5 in an area that is approaching or exceeding the NAAQS and are not located near a state operated PM_2.5 ambient monitoring station should consider measuring site-specific background PM_2.5 concentrations (e.g., as a substitute for air dispersion modeling).
• Per- and polyfluoroalkyl substances (PFAS) deposition. For years, U.S. EPA has assessed PFAS concentrations in water. As U.S. EPA looks at this problem in depth, additional pathways are being considered, one of which is deposition of air emissions, with initial research projects to gather data to understand the problem.
• Community Interest/Environmental Justice Considerations. With the focus of this administration on environmental justice (EJ), about $170 million in grants to fund air quality monitoring for communities are included in the American Rescue Plan Act (ARPA) and the Inflation Reduction Act (IRA). You may need to conduct ambient monitoring to address community concerns about ambient impacts from your plant, especially if they employ small inexpensive sensors near your facility. It is also conceivable that in a state with an EJ rule you could be required to implement fenceline monitoring as part of a project if your facility is near an overburdened community.

What Does This Mean for My Facility?

If your facility is covered by one of the recent rules that includes fenceline monitoring, there are dates by which you must begin your monitoring program. Given the variations in monitoring requirements, action levels, and root cause/corrective action, consider conducting a pilot sampling program in 2024 to understand current emissions, areas of concern, and any corrective actions ahead of required monitoring deadlines. If you have already been conducting fenceline monitoring and are approaching or are over applicable action levels, you will need to conduct a root cause analysis and perform corrective action to reduce monitored impacts.

If your facility has PM_2.5 emissions sources, you may need to develop a strategy around how you will deal with the lower PM_2.5 NAAQS, which could include ambient monitoring. If your facility is subject to a NESHAP that U.S. EPA has not reviewed in a while (they are required to review NESHAP every eight years), stay up to date on what changes U.S. EPA is proposing to make and whether fenceline monitoring is included. If your facility is near a community that is interested in your air emissions, know what their concerns are and how you can address them.

How can ALL4 help?

ALL4 can help you navigate fenceline monitoring requirements and track other initiatives that may result in a need for ambient monitoring. ALL4 has helped many industries navigate ambient monitoring requirements with years of experience in strategy development, planning, execution, and mitigation. We can provide any of the following services:

• Developing an approach for procuring and siting equipment and executing a successful ambient sampling and monitoring program.
• Monitoring plan and quality assurance project plan (QAPP) development.
• Monitoring and sampling equipment installation and operation.
• Collection, processing, and submitting samples for analysis.
• Data review, data calculations, and interpreting sample results.
• Conducting quality assurance audits to verify the collection of representative samples.
• Preparing electronic reports for agencies and the U.S. EPA.
• Preparing root cause analysis and corrective action plans if your facility exceeds concentration action levels.

For more information, please contact Kyle Hunt at khunt@all4inc.com or 512.705.0123.