Episode 670: Charles J. Weschler, PhD Ozone, Hydroxyl Radicals and Indoor Environments; What Inspection and...

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Episode 670: Charles J. Weschler, PhD Ozone, Hydroxyl Radicals and Indoor Environments; What Inspection and...

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Show Resources: Show Discussion:

12:08:43 From Ken Larsen : I would love to see Weschler speak at Summer Camp about this stuff.
12:11:24 From Kishor Khankari : what is isoprene?
12:15:23 From Kishor Khankari : Does indoor hydroxyl help in improving IAQ?
12:16:27 From Bud : The smell when rain starts is called petrichor. What is that ?
12:17:48 From Ralph Froehlich : Geosmin may also be released by toilet paper and paper towels.
12:19:22 From Danny Gough : O3 is nearly a profane word within the EPA. But its used around the world for everything from air purification to medical treatment. Why the disconnect?
12:19:40 From Kishor Khankari : Does it mean UV-C fixtures produce ozone?
12:22:11 From Bud : Is breathing high indoor concentrations of negative air ions produced by ionizers bad for health ?
12:25:51 From Kishor Khankari : If Hydroxyl radicals have short life then why to worry about it?
12:26:04 From Darren Hudema - PuroClean Academy : Understand what effect to radicals have on the human body, when narrative in the industry say that Hydroxls are safe to use in occupied buildings.
12:27:30 From Darren Hudema - PuroClean Academy : What are byproducts related to Hydroxls, and possible affects to the human body or animals etc.
12:28:58 From Danny Gough : I recall that a specific HVAC manufacturer made an air cleaner that produced hydroxyl radicals through PCO. Researchers allegedly determined the process produced formaldehyde. Are these reactions capable of this behavior?
12:29:48 From Sean Scott : Byproducts of ozonation can create methyl cyanide, bromomethane, and formaldehyde. Can hydroxyls create these same hazardous gases?
12:32:15 From John Lapotaire : What happens to the smaller pm such as the pm 0.3 when the pm 2.5 is reduced?
12:35:03 From Kishor Khankari : As you mentioned the byproduct of OH reaction is ROO radicals, do these ROO radicals help improve indoor air quality?
12:35:08 From Lorne McIntyre : Can we get article info ?
12:35:26 From Danny Gough : I think I heard hydro peroxides. There is a company promoting a device that uses UV light targeted on a quad metallic catalyst to product airborne molecules of aerosoled hydrogen peroxide. Any literature showing if this is effective or harmful?
12:35:52 From Ken Larsen : ?? HO per "cubic centimeter?... or cubic meter? (big difference)
12:45:27 From Kishor Khankari : Do these peroxides byproducts have sanitizing effect on airborne pathogens?
12:46:03 From Bud : If ionizers reduce PM2.5 by increasing PM2.5 to indoor surfaces doesn’t that mean that respiratory deposition is increased ?
12:47:56 From Sean Scott : Byproducts of ozonation can create methyl cyanide, bromomethane, and formaldehyde. Can hydroxyls create these same hazardous gases?
12:51:12 From Danny Gough : PCO > Titanium Dioxide > Hydroxyl Radicals is STILL be promoted.
12:52:32 From Lorne McIntyre : Claims made by manufacturers that hydroxyls free radicals destroy microorganisms true or false. Same for mold spores and viruses. Thanks
12:54:16 From Darren Hudema - PuroClean Academy : CDC Position on Emerging Technologies for Air Cleaning: As with all emerging technologies, consumers are encouraged to exercise caution and to do their homework. Registration alone, with national or local authorities, does not always imply product efficacy or safety. Consumers should research the technology, attempting to match any specific claims against the intended use of the product. Consumers should request testing data that quantitively demonstrates a clear protective benefit and occupant safety under conditions consistent with the intended use. When considering air cleaning technologies that potentially or intentionally expose building occupants, the safety data should be applicable to all occupants, including those with health conditions that could be aggravated by the air treatment. In transient spaces, where average exposures to the public may be temporary, it is important to also consider occupational exposures for workers that must spend prolonged periods in the space.
12:55:04 From Darren Hudema - PuroClean Academy : Preferably, the documented performance data under as-used conditions should be available from multiple sources, some of which should be independent, third-party sources. Unsubstantiated claims of performance or limited case studies with only one device in one room and no reference controls should be questioned. At a minimum, when considering the acquisition and use of products with technology that may generate ozone, verify that the equipment meets UL 867 standard certification (Standard for Electrostatic Air Cleaners) for production of acceptable levels of ozone, or preferably UL 2998 standard certification (Environmental Claim Validation Procedure (ECVP) for Zero Ozone Emissions from Air Cleaners) which is intended to validate that no ozone is produced.
12:57:11 From Sean Scott : How can restorers verify that toxic byproducts resulting from hydroxyls oxidation don’t remain after a smoke remediation project?
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Re: Episode 670: Charles J. Weschler, PhD Ozone, Hydroxyl Radicals and Indoor Environments; What Inspection and...

Post by CliffZ »

Great audience involvement today!
Nuggets mined from today’s episode:
• Ozone, because it can be easily measured, has been studied by scientists since the 1860’s.
• Study of OH is new because OHs weren’t on researcher’s radar. Measuring OH requires sophisticated and very costly equipment.

Background info on ozone and hydroxyls:
• The majority of O3 found indoors is from outdoor sources. Normal indoor levels of ozone are 5-20 PPB. Normal indoor levels of O3 are considered livable.
• The OH found indoors is from indoor sources, ozone reacting with alkenes and gases. Indoor OH levels are generally so small that they are measured in molecules per cubic meter 4 X 10¯6 (range from 100,000-1,000,000). Normal OH levels indoors are considered livable.
Conversion for PPB and molecules per cubic centimeter 2.46 X 1010
• O3 reacts with double carbon bonds, approximately 10% of substances found indoors.
• O3 + alkenes generate OH
• OH is much more reactive than O3, wanting to become water it reacts with everything. OH increases oxygen to carbon ratio making substances more water soluble. OH typically pulls off a hydrogen and leaves free radicals. (alkyl peroxy radicals).
• OH reacts with organics much, much faster than O3 reacts with organics (example of isoprene). OH doesn’t get far before it reacts, OH rarely gets to surfaces.
• Geosmin is the pleasant smell of soil and that earthy scent that comes with and after rain.
• O3 does not react with isoprene. OH reacts with isoprene.
• Ozonide is the polyatomic anion O−3. Cyclic organic compounds formed by the addition of ozone to an alkene are also called ozonides.
• Isoprene is a metabolic byproduct. Isoprene is always found in occupied spaces indoors. Indoors when we exercise or eat, isoprene levels go up. Isoprene is ½ a terpene. [Isoprene, or 2-methyl-1,3-butadiene, is a common VOC with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals (including humans).]
• Methacrolein, or methacrylaldehyde, is an unsaturated aldehyde. It is a clear, colorless, flammable liquid. Methacrolein is one of two major products resulting from the reaction of isoprene with OH in the atmosphere, the other product being methyl vinyl ketone. Wikipedia.
[Methacrolein was used to study the effect of parts per billion levels of limonene oxidation products and the terpene oxidation product, methacrolein on human eye blink frequency.]
• The half-life of OH is very short, 10-50 milliseconds. Alkyl peroxides and hydroperoxides are also formed. Hydroperoxides may have adverse health effects.
• O3 removed indoors primarily by surface chemistry.
• OH removed indoors almost exclusively by gas-phase chemistry.
• Very few OH molecules ever make it to a surface.
• Total OH reactivity (s-1) -- define -- recent estimates & measurements indoors
Total OH reactivity of 50 s-1 equivalent to an OH half-life of 0.014 s

Z-Man signing off
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