Sulfuric Acid Mist Sampling and Controlled Condensate (NCASI Method 8a) Testing

Criteria Pollutants and MACT related air toxics such as Mercury and HCl get a lot of attention in the field of air-quality analysis and emissions testing (stack testing), but other, less-known pollutants can and do cause issues for facilities. Sulfuric Acid Mist (H2SO4) is one such pollutant.


Sulfuric acid emissions

Sulfuric acid emissions have traditionally been measured using EPA Method 8. This method utilizes the principle of selective solvent absorption (SSA) and captures sulfur trioxide (SO3) and H2SO4 in an isopropyl alcohol (IPA) solution, and SO3 in a low concentration of hydrogen peroxide. A drawback to this method, however, is that it was developed and originally promulgated to determine SO3/H2SO4 emissions from stationary sources in the absence of other particulate matter. The principal drawback is the absence of a filter to effectively remove PM and other pollutants prior to the capture of H2SO4 in IPA. This can lead to interference from a number of filterable particulates and other pollutants, such as ammonia, and may result in emissions reading much higher than expected, making it difficult to achieve compliance with the emissions standards.


NCASI Method 8a

NCASI Method 8a, originally Conditional Test Method (CTM)-013, was developed as an alternative to EPA Method 8, and uses a heated quartz filter for capturing particulates, thereby eliminating the potential for interference from particulate sulfate and other interference. For sources that are having trouble with obtaining low emissions of H2SO4, and particularly those that have been using ammonia-injection control technology, the use of this method can result in a significant reduction in reported emissions from the source, by removing these varying interferences.

The quartz filter is maintained at temperatures above 500 degrees F, allowing the gaseous SO3/H2SO4 to pass through and be selectively condensed in a temperature-controlled condenser. The condenser cools the flue gases below the dew point of the SO3/H2SO4, but above the dew point of water, eliminating the potential for interference from SO2. The method was developed and validated as an alternative for determining sulfuric acid emissions from combination boilers and recovery furnaces equipped with dry particulate control devices, and tested extensively on kraft recovery furnaces. It was specifically approved by the EPA for use on recovery furnaces in 1996.


Potential Issues

There are two potential issues with utilizing this method. The first is that it utilizes special equipment that not many testing firms have. The equipment costs several thousand dollars, which creates a large up-front cost to conducting tests using this method. The second is that the method is not specifically approved for any units other than recovery furnaces, and compliance tests performed by this method must be approved by state regulators on a case-by-case basis.


Call in the Professionals

ESS, an air-testing firm out of Wilmington, North Carolina, has the equipment and experience to conduct this test method for facilities that are currently or potentially regulated for H2SO4. ESS has requested and received variances from state regulators for use on biomass boilers, paper mills, and ceramic kilns for compliance-level testing. In all cases so far, the use of this alternative method has greatly improved the reported emissions of H2SO4, and helped our clients achieve compliance with the emissions standards their units are subject to.

If your facility is expected to be regulated for sulfuric acid mist, you need a testing partner that can achieve the best results. Give ESS a call today at  (910) 799-1055.

Brian Mellor About Brian Mellor

Brian Mellor works with Environmental Source Samplers, Inc. (ESS), an environmental consulting firm specializing in stack testing, CEMS Testing, and EPA air emissions compliance.

ESS has conducted international stack testing projects at Johnson Atoll, in the Philippines, the Dominican Republic, Hong Kong, and various parts of Europe. If you need a team that will do your international job with efficiency and effectiveness, call ESS at (910) 799-1055 or visit

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