Overcoming the Stack Testing Challenges of PM and Method 201a

Stack Test MethodologiesParticulate Matter (PM) is the term for solid or liquid particles found in the air – more accurately referred to as aerosols. Worldwide, most atmospheric aerosol particles (approximately 90%) are produced by ‘natural’ processes such as grinding and erosion of land surfaces resulting in dust, salt-spray formation in oceanic regions, biological decay, forest fires, chemical reactions of atmospheric gases, and volcanic injection. The balance of the PM is anthropogenic in source – from industry, agriculture, transport and construction. Particulate size, elemental breakdown and color can vary significantly between the many sources.

PM can have high levels of toxicity and is considered by the Clean Air Act as one of the Criteria Pollutants. Originally, the focus has been on Total Suspended Particulates (TSP), but over the past decade the EPA has put a greater emphasis on the measurement of smaller particles, those less than 10 and 2.5 microns in diameter (PM10 and PM2.5). This is due to the greater health risk associated with the smaller particles, which are capable of reaching into the lower regions of the respiratory system.

From an emissions sampling standpoint, this has increased the importance of quantifying emissions in specific size ranges, rather than the analysis of total filterable particulate (by EPA Method 5). The most widely accepted methodology for determination of PM10 and PM2.5 from stationary sources is Method 201a. This isokinetic method requires some of the same sampling equipment as Method 5, but includes the addition of sizing cyclone(s) upstream of the PM filter. What is not as well-known are the multiple challenges and limitations with Method 201a that can hamper testing or even make it unfeasible. Many of these challenges can be mitigated but require knowledge of the stack condition prior to the sampling date. Some of these major challenges are summarized below.

Test Port Size – As mentioned, the method requires a particular set of equipment: a probe (equipped with special pitot tube extensions and temperature sensor), in-stack PM sizing cyclone(s) and a nozzle. The cyclone and nozzle combination required for the method are typically stainless steel, inflexible, and have a wide circumference, often wider than the test ports installed in some of the older stacks. Method 5, typically, only requires 4″ test ports, but the 201a equipment requires a test port of 6″ minimum to fit the sampling probe inside, so a facility that is not prepared for 201a testing may find that its test ports are too small and testing cannot take place. Further, if the test port is long, an 8″ (minimum) test port may be required to prevent the nozzle from scraping the inside of the port wall. We urge our clients to properly verify test port configuration prior to our arrival on-site.

Moisture Level of the Stack (Saturated Stacks) – If water droplets are present in the stack, it is not possible to utilize the Method 201a cyclone. The spherical nature of PM is assumed when utilizing the Method 201a cyclone. If moisture is present, this can cause conglomerations of the PM and also cause the PM to stick to the cyclone walls. Additionally, the moisture-laden aerosol mists do not act spherically – thus biasing the results. The EPA-accepted measurement of fine particulates in saturated stacks is Method 5/202, which adds the total filterable PM and the condensable particulate matter (CPM). Although the US EPA has defined PM10 (or 2.5) in a saturated stack as the sum of the PM + CPM, it is clearly an overestimation of the stack emissions.

Temperature of the Stack – Another challenge with the method is dealing with the heat of the gas stream inside of the stack. If the stack gas temperature is over 30 degrees C (85 F), then the Facility must account for the measurement of CPM by Method 202. Therefore, PM10 (or 2.5) is measured as the sum of the filterable fine fraction plus the CPM.

Some of the equipment used in typical 201a trains has a temperature limit of approximately 260 degrees C (500 F) before problems occur with seizing, galling, or thermal breakdown. The method can be used at temperatures of up to 1,371 degrees C (2,500 F) but, in order to do this, it requires the usage of specialty high-temperature resistant material, which generally must be procured or prepared beforehand, and which can drastically influence the price of the testing.

Other Sampling Options/Purpose of Sampling – ESS frequently conducts engineering testing for clients evaluating flue gas streams for particulate matter. The analysis of such streams can provide useful information to control device manufacturers, efficiency experts, and boiler engineers. Although EPA Methodology is required for demonstration of compliance, ESS typically recommends other sampling methodologies for engineering testing.

Such methodologies can include isokinetic sampling on specialty media and analysis utilizing x-ray diffraction, computer-controlled scanning, electron microscopy, or GC/MS scanning. ESS frequently provides in-depth particulate analyses including particulate sizing and elemental composition. Depending on the goals of the sampling, ESS will propose the best methodology to meet your required outcome.  Read more about Stack Test Methodologies ESS is qualified to conduct.

Summary – These factors – port size, stack moisture level, flue gas temperature, and the purpose of the sampling – are all important considerations for your PM test series. The Method 201a/202 test takes more preparation than many other emissions test and requires more communication between the facility and the professional stack testing company being used for the conduct of the test.

As in all things, experience is the key to success. ESS has conducted hundreds of tests for PM, CPM, PM10 and PM2.5 since 1979 and has the knowledge and experience to provide reliable and acceptable results for your engineering or compliance test program. If you require PM/PM10/PM2.5 testing – or other air emissions sampling services – give ESS a call today: 888-363-0039

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 www.ESSKnowsAir.com.

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