Air Toxics Assessments: The Challenges of Designing an Affordable Monitoring Network

The state of Oregon has proposed a new set of rules, currently in the draft state, for a risk-based air toxics permitting program; the program is named “Cleaner Air Oregon.” The stated goal of Cleaner Air Oregon is to reduce health risks from existing industrial facilities to below 100 in 1 million by 2030. To accomplish this goal, the state of Oregon will require emissions reductions from facilities for which the aggregate health risk, based on predicted health risk from 260 chemicals with known health-protective levels, is above the 100 in 1 million threshold.

Portland Oregon Air Toxics

Portland, Oregon

A health risk assessment of each facility will be established based on predicted ambient concentrations of air toxics, which are determined using air quality models coupled with an emissions inventory of each facility. In addition, facilities may perform monitoring to determine the actual ambient concentrations of air toxics around the source for comparison to the modeled concentrations. The elective monitoring program under the current proposed draft rule of Cleaner Air Oregon has many requirements. Among these are: monitoring must be performed for at least 12 months with 75% data completeness per quarter, a monitoring plan and a community engagement plan must be drafted, and monthly and annual reports must be submitted to Oregon DEQ.

Considering the requirements and cost associated with an optional monitoring program, why might a facility elect to perform air toxics monitoring? Performing air toxics monitoring in this program may be appropriate under certain circumstances because the cost of implementing control technology can reach into the millions of dollars. If monitored air toxics concentrations are found to pose no significant health risk, then emissions reductions may not be necessary.

There are significant challenges to developing a monitoring program for air toxics. Many of the 260 compounds are either costly to measure or below the limits of detection of federal reference methods for ambient monitoring. In addition, many of the 260 compounds do not have a federal reference method for ambient monitoring and their detection will require potentially new methodology.

To determine if air toxics monitoring is the right approach, the first steps are to evaluate the materials and processes used at your facility, and identify possible air toxics of concern. It may be appropriate to compile an emissions inventory and perform basic dispersion modeling to see if there are target compounds that are being released in high concentrations.

If there are target compounds of concern, the next important step is to determine if and how they can be measured. For the majority of compounds, monitoring is done by sampling continuously for 24 hours onto a filter substrate or into a canister, which is then analyzed in a laboratory. For example, particulate-bound metals such as lead, manganese, mercury, nickel, and cadmium can all be measured with Federal Reference Method IO-3.3, a filter-based method. EPA method TO-15, a canister-based method, can be used for some VOCs (benzene, acrolein, methanol, phenol). However, compounds like chlorine, ammonia, and chromium(III)/chromium(VI) either have costly procedures, have a risk level below the limits of detection for current technology, or have no standard method of measurement.

Determining whether air toxics monitoring is appropriate for your facility will be a balance of the potential costs of implementing controls, the potential compounds of concern, and the diversity of compounds. Each different method of measurement introduces around $50K in equipment costs and increases personnel time for instrument handling, reporting, and other activities. Cost savings can be found by optimizing collection schedules and the number of monitoring locations.

Do you have questions about monitoring for air toxics? Get in touch today.

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