What ‘s the scoop on PM10 and PM2.5 Particles?

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It was December 5th, 1952, only 7 years after the end of WWII in London England when the “great smog” settled across the city.

It was a meteorological anomaly combined with unchecked industrial pollution that led the great smog, but even once it settled on the city, bringing business to a screeching halt, everyone thought it pass quickly.

It didn’t.

4 days later the smog finally lifted and the death toll rose to 4,000. Many modern statisticians place the number of deaths caused by the smog at closer to 10,000. While the world knew the dangers of particles in the air before, there was a keener understanding of what pollution in our air can do to us since that time.

Nowadays you will hear the terms PM2.5 and PM10 thrown around and you may never stop to think about what they mean.

PM10 (Particulate Matter < 10 Microns)

Particles with a diameter less than 10 microns across. For some perspective, a human hair is about 50 – 70 microns across and a micron often called a micrometer is one-millionth of a meter. While a PM10 particle is tiny it still pretty coarse by particle standards and will often contain things like dust, dander, and pollen. These are allergens to be sure but generally are not the most dangerous particles.

PM2.5 (Particulate Matter < 2.5 Microns)

These are particles less than 2.5 microns and often contain things like Ammonia, Carbon, Lead, and mold. Both chemically and biologically toxic particles generally fall into this smaller 2.5 microns or less size range.

Zhao D, Azimi P, Stephens B – Int J Environ Res Public Health (2015)

In the graph shown above you can see the results of the % of PM 2.5 sized particles that passed through some various tested filters. The study showed that not only that typical MERV 6 – 8 filters failed to do a good job of capturing a large percentage of these particles. It also showed that the efficiency of the filters varied from brand to brand as shown in MERV12(#1) and MERV 12 (#2).

Indoor / Outdoor

There is a clear link between pollution outdoors and pollution indoors. It stands to reason that if the air outside is dirty then the air inside will also tend to more particles in it which means that a comparison of outdoor PM2.5 to indoor PM2.5 comparison can be a better way to compare one space to another.

The EPA has tested and found that indoor air can be significantly more polluted with VOCs (Volatile Organic Compounds) often 2 to 5 times more than outdoors.

But hang on…

VOCs are gaseous and are not the same as PM2.5 particles and shouldn’t be confused with them.

From a technicians perspective, you need to be aware that typical air filtration will only effectively deal with the PM10 and larger particles. For the PM2.5 you will need high MERV filtration or other types of active filtration such as PCO or Ionization strategies.

For VOC’s you can ventilate, use carbon filtration or look into products like the Air Oasis bi-polar ionizer that has bee shown to reduce VOCs in studies.

Testing for what exactly is in the air is a trickier business then I initially thought and get’s tougher the smaller the particles get. Even today it is essentially impossible to “test” for specific live fungus, bacteria and VOCs in the field. You can count particles and get in the ballpark of the issue but nailing down all the details can be really challenging without sending samples off to a lab.

For most of us, a good particle counter is the best we are going to get out in the field and we are best off following some good solid practices to help our customers.

  • Encourage your customers to use good quality filters. When possible install MERV12 or better
  • Make sure the unit isn’t pulling air around the filter or through the panels
  • Make sure that ducts are well sealed so that the return isn’t pulling in air from an unconditioned space
  • Keep the indoor relative humidity between 30% – 55%
  • Address any localized moisture issues that may be resulting in organic growth
  • Add in well-filtered ventilation air for VOC reduction
  • Make sure the evaporator, blower wheel and drain pan are kept clean
  • Research quality IAQ products and reccomend them based on your customers needs and desires
  • Bring in fewer VOCs by using indoor products that are more natural and/or have had more time to off-gas

The most dangerous stuff in the air are chemicals, tiny particles and live organisms caused by moisture issues. Knowing this will make you better tech and more capable to advise your customers well.

— Bryan

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