Field demonstration of a near-real-time multi-metals ambient fence line monitor case study


National emissions standards for hazardous air pollutants (HAPs) are required under Section 112 of the Clean Air Act to limit the release of specified HAPs. Permitting, monitoring and enforcement of these emission limits are an integral part of managing air quality to protect human health and the environment. However, this is difficult and highly uncertain in the case of fugitive emissions because of the lack of appropriate monitors. This is of particular concern for fugitive metal emissions because metals represent 8 of 33 pollutants identified by the EPA as posing the greatest potential health threat, and these fugitive emissions may represent dominate exposure pathways in some airsheds. Fence line monitoring- or monitoring in a neighborhood near the perimeter of a metals emission source, offers the potential to not only greatly increase the accuracy of estimating the local impact of fugitive metal emissions, but also has the potential to eliminate the need for costly monitoring of poorly defined emissions from many possible area and fugitive permitted sources. Near-real-time ambient monitoring could also provide hourly or shorter feedback to plant operators to minimize emissions before they become a problem.

Cooper Environmental Services LLC (CES) is currently working on an ambient multi-metals monitoring program in coordination with MACTEC and EPA sponsorship. The overall objectives of this program are to: develop a near-real-time multi-metals ambient monitor, demonstrate its potential utility for permitting and compliance demonstration, and develop reference procedures for its application.

Ail ambient-optimized version of a CES continuous emissions monitor based on reel-to-reel filter tape sampling with X-ray fluorescence analysis of metals lias recently been used to evaluate the feasibility of near-real-time metals measurement as well as the feasibility of apportioning these metals to potential fugitive emission sources. In this field test, the monitor was installed near a metals manufacturing facility and operated for a period of about one month. The monitor (CES Xact 620) recorded hourly concentration (ng/m3) data for the following 24 elements: K. Ca, Sc. Ti, V, Cr, Mil. Fe. Co. Ni. Cu, Zn. Ga. As. Se. Br. Mo. Cd. Sn. Sb. Ba. Hg. Pb. and Bi. Local wind speed and wind direction were also recorded during this same period. A key. new and unique aspect introduced with the Xact 620 multi-metals monitor is its ability to generate large, multi-element data sets applicable to receptor oriented source apportionment models. The resulting database from this field study was evaluated for its applicability to receptor-oriented source apportionment models such as chemical mass balance and multivariate models. These models are well established, validated models having been used for over 30 years as the basis of permitting and compliance demonstration. This capability of defining near-real-time source impacts is expected to be particularly useful in implementing new particulate matter and lead National Ambient Air Quality Standards that require defining source impacts as the basis for further monitoring and development of state implementation plans.

These field tests demonstrated that the Xact 620 ambient metals monitor is field ready by providing metals concentration data over the course of the field test. This conclusion is further supported with the deployment of six similar ambient metals monitors at various locations around the world. The monitor detected real world concentrations of various metals from low background levels to high concentration events. Not only did it respond timely to rapidly changing concentrations of elements from an expected source, but it recorded 'hits' from two unexpected sources, one dominated by Pb and Zn and the other dominated by As. In addition, the data generated by the monitor was determined to be adequate for application to EPA's Chemical Mass Balance 8.2 source apportionment model. Thus, both the measurement and modeling technologies are available for permitting and enforcement applications. The monitor provided all of the required ambient data for the model. It could provide source profile information through multivariate analysis if source profiles are not available from the EPA source profile library or through direct measurements of emissions that might be required as part of a permitting and enforcement plan.

It is important to note that this field-ready feasibility evaluation study has clearly shown that with near-real-time monitoring, events may be observed that might otherwise be obscured with 24 hour integrated sampling with laboratory analysis. If these events can be observed, it should be possible to regulate and or eliminate them through permitting, enforcement and improved plant management. In addition, measured short-term peak impacts may be directly related to specific fugitive emission events and/or processes, which again may be eliminated through improved plant management.

The following tasks still need to be completed prior to using this technology in a permitting and enforcement setting:

  1. Validate FLM analytical results by comparing to EPA federal reference methods
  2. Automate and integrate CMB 8.2 source apportionment model into the FLM
  3. Develop protocol for permitting and compliance demonstration
  4. Field demonstrate total system protocol

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