• Jul 16, 2021
  • Particle Size
  • By William Kopesky

Our Roots as Experts in PM10 and PM2.5 Testing

Did you know Particle Technology Labs began as a testing service for companies needing to meet EPA environmental safety standards? While we are most known today for our testing for the pharmaceutical industry and our commitment to cGMP quality assurance regulations, some will be surprised to learn that the company’s early services were in testing environmental emission and water filtration samples. Now, almost 30 years later, we still assist companies in these industries including some of those first clients who are still with us today!

Testing for PM10 and PM2.5

The founder of Particle Technology Labs, Richard Karuhn Sr., started the company by providing analysis of stack emission samples for PM10 and PM2.5 in 1992. He not only tested them – he spent time collecting them as well!

What do PM10 and PM2.5 stand for? Glad you asked. PM is an abbreviation for “particulate matter.”  PM10 or PM2.5 is the particulate matter in an emission sample that is less than 10 or 2.5 micrometers respectively by mass. These sizes are of interest to the USA Environmental Protection Agency (EPA) as particles in this size range are not easily filtered out by the nasal passages nor impact the back of the throat for removal when we breathe. Particles less than 10 micrometers will enter the lungs and can cause both acute and chronic respiratory issues. Factories, power plants, and similar types of companies are required to monitor and control their emissions for these particles or risk expensive fines and/or production shutdowns.

Sample Collection Methods for Plant Emissions

Plant emission samples can be collected by a variety of EPA methods (referred to by numbers such as EPA Method 5, 201A, 202, and 17) depending on the source, design, and environmental conditions inside the emission stack. Many of the EPA methods use a “sampling train” consisting  of several sophisticated parts and pieces operated under controlled conditions such as temperature.  The diagram below is an example and illustrates the main sections in a sampling train.


Sampling TrainMain sections of a sampling train. (Image taken from rental.cleanair.com)

The probe section of this device is inserted through the wall of the emission source, often a tall stack routinely seen outside of a factory or power plant, similar to the image below.


Smoke Stack

This testing is not for the faint of heart! The tester must often climb up 100s of feet to the platform around the stack, haul up the testing equipment and then perform the test over potentially several hours depending on the emission source and concentration! The sample is collected “isokinetically,” which means the air sampling rate is set to match the air velocity of the stack emission. The probe can also be inserted into the stack at different distances across the stack diameter, depending on the length of the probe and stack diameter. This sampling pattern allows for a representative sample of the gas stream as the flow of the gas inside the stack is parabolic in shape (e.g., slower against the walls of the stack and faster in the center). The variation in air velocity within the stack can cause biased particle size results if not sampled correctly. Needless to say, the samples collected need to be handled with care and precision as the cost of resampling can be very expensive.

The physical sample is collected by pulling a vacuum on the sampling train, and the emission gas is drawn into the probe. Large particles are deposited in the probe tube, while the smaller particles travel down and are collected on a filter inside the heated filter box. The box is heated to prevent any moisture in the stack gasses from condensing on the filter and potentially biasing the mass collected or causing agglomerations of the particles. The stack gasses are finally drawn through glass tubes filled with a liquid called impingers which collect dissolved compounds such as sulfuric acid and other chemicals which might be present. Prior to testing, the stack tester will obtain an initial blank weight of the filter and then reweigh the filter after the test is performed. In addition, the particulate deposited in the probe is rinsed out and collected in a pre-weighed beaker. The liquid is dried down, and the mass of the probe particulate is also determined. The total mass of solids collected (probe + filter) allows the stack tester to report the mass per time for regulatory compliance as well as evaluate emission control efficiency.

Testing the Air Sample

Once the stack testing company has determined the total mass collected (referred to as the gravimetric results), they send the dried probe rinse and filter to PTL for particle size testing. Particle Technology Labs then determines the particle size distribution from the probe rinse and filter catch using the most appropriate technique based on the amount of particulate available, the size range of interest, and other relevant factors. Using the particle size results, the PM10 and PM2.5 can be determined.

In the example below and for easy math, let’s say the PM10 is 50% and the PM2.5 is 25%. The gravimetric results determined by the emission testing company found approximately 100 mg of mass collected in the probe and on the filter combined over an 8-hour shift. Using the results provided by PTL, the plant manager can now see they are producing approximately 6 mg/hr of particulate <10 µm and 3 mg/hr particulate <2.5 µm. These values can be compared to previous results to assess if the emission control equipment/process is operating correctly, has changed over time, or is in compliance with regulations. The actual calculations are performed by the emission tester, and several variables are included for the most accurate results, so this is just a simplified example.


Emission Tester


When we say it’s never a dull moment, nor do we know what will arrive on a daily basis here at PTL, we mean it! Active pharmaceutical ingredients (APIs), stack emission samples, food products, water filtration samples, cosmetics, the list goes on. Particle characterization can help a vast array of industries. Particle Technology Labs has the experience, equipment, and knowledgeable staff to perform your particle testing needs. Give us a call or use the text chat in the lower right to discuss how we can assist in helping you gain a better understanding of your products, processes, and particles! Learn more about our environmental testing services.

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