“The World Health Organization (WHO) has stated that air pollution is the greatest threat to human health today. The smallest and most dangerous fraction is PM1. It is so dangerous that we need to protect ourselves against it. The industry is responding. That is why we welcome ISO 16890 – the new industry standard to measure a filter’s efficiency to remove PM1. It will help our customers select the right filter to remove PM1 and improve health. This will reduce society’s medical and health leave costs. We fully support these efforts.”
The above quote comes from a video clip produced by one of the major multinational filter manufacturers. Sounds good. Who would not be in favor of reducing PM1 to improve health and reduce society’s medical and health leave costs? The only problem is that this conclusion is not a function of the operative statement – “That is why we welcome ISO 16890 – the new industry standard to measure a filter’s efficiency to remove PM1.” Adopting ISO 16890 will not change the filters tested. It will not change the air handlers in which they are used. It will not change the amount of time the HVAC systems are running. It will not change the indoor environments in which the filters are used. In and of itself, it will not reduce PM1. As has been pointed out in a previous discussion, ISO 16890 is an air filter testing standard – nothing more. It’s adoption by the USA will not improve health.
However, we do agree that it is an admirable goal to reduce exposure to PM1 particles. As Dr. William Fisk, Senior Scientist at Lawrence Berkeley National Laboratory, points out in his presentations on “Indoor Particle Mitigation with Filtration” moving to higher filtration levels (MERV 13) makes sense from both a health and economic point of view. Although, “evidence of health benefits from improving filtration in homes, offices, and schools for those without allergies and asthma is limited.”
In a recent “open letter” produced by a major multinational filter manufacturer there is this quote: “Additionally, ISO 16890 takes an added step to better classify lower efficiency filters (such as pleated panel filters) by using two different PM curves to evaluate products. Filters classified as ePM1 or ePM2.5 are evaluated using a typical published urban particle distribution, while ePM10 products use a typical published standard rural particle distribution.”
Again sounds great, but what do they mean when they say urban particle distribution and rural particle distribution? Here is a brief explanation from an article in the ASHRAE Journal -May 2016 by Tronville and Rivers entitled “New Method for Testing Air Filter Performance:”
“The ISO 16890 set differs from ASHRAE Standard 52.2 and the European Standard EN 779 chiefly in basing its rating system on calculations of the mass of particles captured by the filter from two standard aerosol particle distributions. The aerosol models used are bimodal, having two distinct peaks, one approximately 0.3 um and the other having approximately 10 um. Both modes are defined in terms of mass of particles. This bimodal pattern is found worldwide: the mode with smaller size (urban) is primarily due to combustion, while the mode with larger size particles (rural) is the result of soil particles lofted by winds. Calculations specified by the standard yield efficiency numbers, designated ePM1, ePM2.5 and ePM10, which represent the performance of the filter for three different size ranges of the standard distributions. The number ePM1 is essentially the efficiency for particles with a size of less than 1 um; ePM2.5 for particles less than 2.5 um; and ePM10 for particles less than 10um. These ranges are related to the particle-matter (PM) air pollution data gathered by the government agencies in many countries.”
In other words, based on outdoor air quality measurements and the differences in particle distribution between rural and urban environments two separate particle distribution models are used in ISO 16890. The premise on which this is based is false – at least for the United States. It assumes that all particles captured by a filter are of outdoor origin. In fact, most of the particles captured by the filters are of indoor origin and are caused by activity in the space. Anyone with a particle counter can prove this quickly. Take a particle count when the building (like an office or school) is occupied and a particle count when the building is unoccupied. The occupied reading is always higher than the unoccupied reading – usually many times higher. The outdoor air is exactly the same. So the only source of this differential is the activity in the space.
In a previous article I used the example of a study done on particles in schools. The article is:https://www.texairfilters.com/the-usa-should-not-adopt-iso-16890-for-air-filter-testing-heres-why/. The study shows that indoor particles in the PM1 range were about 10% of the particles outdoors in the PM1 range. The filters used were the “rural” – “low efficiency pleated filters.” Is it logical to assume that “urban” filters would do substantially better? Enough to affect human health? This is very unlikely and certainly not proven by any study or data.
The HVAC systems in this school study were designed to bring in fresh ventilation air when the indoor air exceeded set thresholds of CO2. By bringing in outside air (even a relatively small amount in relation to the overall air in the space), the building was brought into positive differential pressure with the air outside. The positive pressure acted to repel additional particles from entering the schools from the polluted outdoor environment. This is a very common design for buildings in North America. Of course, if one has windows or doors open to improve ventilation (or for comfort), the protective effect of the positive pressure is lost. That is a moot point in this discussion since air coming into a building from outdoors through an open window is not filtered.
The school example is not an anomaly. It is what happens in indoor air. I use particle counters in my office continuously. Yesterday our office was closed and there was no activity inside the building. The average particle count at 0.5um per cubic foot was 11,500. Today the particle count with all of the activity of humans in the space was 220,100 at 0.5um per cubic foot.
The net result is that the particles captured by a filter are a mixture of outdoor and indoor particles. Actually, the particle distribution used in ASHRAE 52.2 much more closely reflects this reality. This is true whether the filter user is in a “rural” or an “urban” area.
(NOTE: I have asked several indoor air scientists to review this paper and their consensus is that outdoor air entering through open windows and doors is understated. In most areas of the world, open windows and doors are the primary method of ventilation for the vast majority of buildings. At least for six months of the year large quantities of potentially polluted outdoor air enters the indoor spaces. This air is unfiltered and overwhelms the ability of any system to effectively remove particles. The result is the use of ISO 16890 testing to address high levels of PM1, PM2.5 and PM10 is meaningless for much of the year in the vast majority of buildings around the world.)
As we have explained in a prior article, pleated filters using electret media are much more efficient at removing PM1 particles than pleated filters using mechanical only media. This advantage in PM1 removal remains throughout the useful life of the filter. By using the arbitrary and incorrect “rural distribution” particle curve for ePM10 filters, one negates this fact. In addition, the use of the phrase “evaluated using a typical rural particle distribution” is pejorative and biased. Gee, who would want to buy a “rural” filter if you live in an urban area? The more you look at it – the more one comes to the conclusion that many aspects of ISO 16890 are based on marketing – not science.
The bottom line is this. ISO 16890 sounds really great on the surface. I am all in favor of a fair, impartial and accurate international standard for testing air filters. However, if you look deeper, ISO 16890 has some significant problems that would make it unsuitable for filter users in the USA. The attempt to ascribe some higher benefit to the air filter testing standard related to outdoor air quality measurements which resulted in the flexible use of PM1, PM2.5 and PM10 versus ePM1, ePM2.5 and ePM10 renders ISO 16890 hopelessly flawed. It will not reduce PM1. It will not improve indoor air quality. It will not improve health outcomes.
Adopting ISO 16890 by the USA would be a mistake with serious consequences for the air filtration market in the United States and for our air filter users.