IAQ RADIO+
Show Number: 769 draft blog
Dustin Poppendieck, PhD
NIST
Evaluating Air Cleaning Technologies
Good Day and welcome to IAQ Radio+ episode 769 Blog. This week we welcomed back Dr. Dustin Poppendieck to discuss methods for evaluating air cleaning technologies. Air cleaning technologies can be complicated and it’s hard to know who you can trust.
Dustin Poppendieck is an environmental engineer at the National Institute of Standards and Technology (NIST). He received his PhD in Civil and Environmental Engineering from the University of Texas at Austin in 2002. He is a fellow of the International Society for Indoor Air Quality and Climate (ISIAQ). Dustin has been investigating indoor air chemistry since 2002. Most of his efforts have involved characterizing primary emission sources and heterogeneous reactions at material surfaces. He has investigated emissions from kerosene can lamps used by nearly a billion people throughout the developing world, spray polyurethane foam, non-smoldering cigarette butts and indoor air cleaning devices. In addition, Dustin has studied the disinfection of biologically contaminated building materials (i.e., anthrax) using high concentrations of ozone, chlorine dioxide, hydrogen peroxide and methyl bromide. Recently, Dustin has been involved in writing and revising standards related to chemistry of portable air cleaners, including ASTM D8625, UL867, ASHRAE 241 and ASHRAE 145.4.
https://www.nist.gov/people/dustin-poppendieck
Nuggets mined from today’s episode:
The field of IAQ research has changed significantly over the past 20 decades. University of Texas (UT) was an early pioneer in IAQ research. Shift of outdoor air quality people now studying indoor air quality and great research and modeling work is being done in China. In the last 5 years, NIST’s ventilation engineering group has been studying emissions relationship with IAQ. Research interest include emission from flame retardants, cigarette butts (slowly release nicotine), cooking emissions, efficacy of low cost sensors, trace ozone levels in homes, air cleaners, and are now quantifying chemicals found in indoor air.
Why is there a growing interest in air cleaners? It’s money in combination with raised awareness due to Covid and wildfires. The importance of keeping schools open. Greater demand for air cleaners has increased the number of manufacturers vying for sales. Suppliers’ needs to differentiate resulted in manufacturers combining multiple old technologies. Some manufacturers benefit from false claims. Several lawsuits use non-consensus-based science to support or refute product claims. A level playing field is needed. NIST is not a regulatory agency. NIST provides unbiased science and collaborates with standards writing organizations (e.g. ASHRAE, ASTM, etc.), NIST is part of the US Dept. of Commerce, increasing consumer wellbeing by creating a healthy marketplace.
NIST Standards and Research Updates
Dustin discussed his work at NIST, focusing on standards harmonization and chemical migration research. He mentioned having three postdocs working with him, including one studying chemical migration through HRV and ERV cores.
NIST Research on IAQ Standards
Dustin Poppendick discussed ongoing research at NIST, including studies on air quality, chemical interactions in indoor environments, and the impact of wildfire smoke on homes. He highlighted a recent paper on chemical persistence in homes and mentioned upcoming research on cleaning methods for wildfire-contaminated houses. Dustin also explained NIST's role in developing consensus standards with organizations like ASTM and ASHRAE, noting that these standards are not regulatory but provide guidelines for best practices. The discussion concluded with a brief overview of IAQ Radio's sponsors and a trivia question.
Air Cleaner Testing Standards Development
Dr. Dustin Poppendick discussed his work at NIST, focusing on indoor air quality and ventilation, particularly the chemistry of air cleaners. He explained that recent interest in air cleaners is driven by COVID-19 and wildfire events, leading to increased demand and the need for standardized testing methods. Dustin highlighted the development of ASTM D8625-2025, a standard test method for assessing the chemical performance of air cleaning technologies, emphasizing the importance of creating a level playing field for companies in the market. There are two basic types of air cleaners: those which are subtractive and don’t add anything to the environment (e.g. filtration, carbon absorption) and those which add chemistry or energy (e.g. UV lamps, ionizers, precipitators, photocatalytic oxidizers, vaporized peroxide, hydroxyls). There is leeway in the standard that allows manufacturers to do specific testing on target chemicals (e.g. methylene chloride, acetaldehyde, etc.)
ASTM Standard for Air Cleaner Testing
Dustin explained the development of ASTM D8625, a technology-agnostic standard for evaluating the chemical performance of air cleaners. He described the standard's goals, including testing realistic concentrations and secondary chemistry, and emphasized the importance of representing real-world conditions in laboratory settings. Dustin also discussed the different types of air cleaners, such as passive and additive systems, and highlighted the challenges of creating test methods that are fit for regulatory purposes.
Air Cleaner Noise and Performance
Dustin explained that while D8625 does not measure noise, it is an important factor for in-room air cleaners as they are often turned off due to noise. He discussed the challenges of measuring airflow and how humans cannot feel airflow below 0.1 meters per second. He provided the example of when touching a metal surface and wood surface in the same room the metal feels colder. The surface temperatures of both materials are the same the difference in temperature is due to energy exchange between the hand and the metal.
Dustin also explained the AHAM two-thirds rule for sizing air cleaners and shared insights from tests on the effectiveness of air cleaners in different room configurations. It was surprising to learn that when an air cleaner is properly sized for the space and doors are closed, that within minutes the air cleaner will mix the air in the room.
Air Purifier Emissions and Testing
Dustin explained that the measured clean air delivery rate was four times lower than lab measurements due to HVAC system effects, emphasizing the importance of proper space sizing and air flow. He discussed that while some air purifiers can produce byproducts like formaldehyde and ultrafine particles, ASTM D867 testing shows that photocatalytic oxidation systems, ionizers, and other technologies can create various byproducts depending on the specific device and operating conditions. Dustin also clarified that while some air purifiers may produce trace amounts of ozone, they are still considered low-emission devices under California regulations, which require testing and certification (<5 ppb, 350-400 micrograms per hour).
Air Purification Technologies Safety Discussion
The discussion focused on the effects and safety of various air purification technologies, particularly hydroxyl radical generators, UV systems, and ozone emitters. Dustin explained that hydroxyl radicals react with everything in the air and advised against being in spaces where these devices are operating due to potential health risks. He also detailed the differences between UV systems using 254 and 222 nanometer wavelengths, noting that 254 nanometer UV light is effective for inactivating airborne pathogens but can create indoor chemistry, while 222 nanometer UV light is safer for humans but may not penetrate surfaces as effectively. The group discussed the potential for these devices to create ozone and the importance of proper placement and line of sight for effective air purification.
UV Air Purification System Discussion
The discussion focused on UV air purification, where Dustin explained that while UV systems can reduce background concentrations of pathogens, they are not effective against direct person-to-person transmission, which requires masks. Dustin emphasized the importance of proper sizing based on the AHAM two-thirds rule and recommended looking for units with low noise levels and high clean air delivery rates that maintain performance even at lower settings. The conversation concluded with Dustin noting that vaporized hydrogen peroxide (VHP) could be an interesting application for pathogen reduction, though it requires careful handling and further research.
ASTM D8625-25 Standard Test Method for Chemical Assessment of Air Cleaning Technologies
This test method covers the measurement of the removal rate of injected challenge chemicals and ultrafine particles by portable air cleaners. This test method also evaluates the extent that portable air cleaners produce a limited set of reaction byproducts: formaldehyde, ozone, nitrogen oxides (NOx), and ultrafine (<300 nm) particles.
UL 867 - Electrostatic Air Cleaners
The Standard for Safety for Electrostatic Air Cleaners. This Standard addresses the safety of portable and fixed (including duct-connected) electrostatic air cleaning equipment. Standard UL 867 is also used to evaluate portable and fixed ion generators.
ASHRAE Standard 241, Control of Infectious Aerosols
ASHRAE Standard 241, Control of Infectious Aerosols, establishes minimum requirements aimed at reducing the risk of disease transmission through exposure to infectious aerosols in new buildings, existing buildings, and major renovations.
ASHRAE 145.4P is a proposed standard for a "Method of Test for Assessing the Gas-Phase Performance of Air Cleaning Devices and Systems in a Duct-Chamber Apparatus". This standard is in development to provide a consistent test method for evaluating the performance of air cleaning equipment that removes gases, odors, and volatile organic compounds (VOCs). The goal is to establish a reliable test procedure for gas-phase air cleaners, which are often more difficult to rate than particulate filters.
Other comments by Dustin Poppendiek
About UV Lights-
• 254 NM UVC light has been used since the 1950s where it was found effective against tuberculosis. It penetrates, making it effective against biofilms and harmful to the eyes and skin of humans, so it is mounted on upper walls or inside ductwork. Needs line of sight, air needs to be moved to device for efficacy. NOX radicals are produced when ozone is separated.
222 NM is a higher frequency UV light that doesn’t impact human eyes and skin. It doesn’t penetrate, so it isn’t effective on biofilms. Below 240 NM the lights will produce measurable amounts of ozone. Do you have enough to be effective or too much causing O3 chemistry. Secondary chemistry (e.g. reacts with squalene resulting in odors.)
• Reactive indoor chemistry: low side creates formaldehyde and on the heavier side creates ultrafine particles.
• Air cleaners are rated at the highest fan speed. If you want to operate device at lower speed for noise reduction, you’ll need either multiple devices or a higher capacity.
• Air cleaners need to be sized properly, AHAM 2/3s recommendation (200 sq.ft. room needs 300 CFM)
• Air cleaners don’t work unless they are turned on!
• Vaporized Hydrogen Peroxide (VHP) is an up-and-coming technology. Insufficient research on VHP currently exists.
Z-Man signing off:
Trivia Question: In what year did the U.S. government adopt a uniform set of standards for weights and measures?
Answer: 1838