Calculating Ozone Levels from Air Purifier Output: Converting mg/hr to ppb

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SUMMARY

This discussion focuses on calculating the ozone levels produced by an air purifier that emits 360 mg/hr in a 2500 square foot space with 10-foot ceilings. The calculations indicate that running the unit for one hour could produce approximately 270 ppb of ozone, significantly exceeding the safety threshold of 50 ppb. The discussion highlights the importance of considering natural dissipation rates of ozone, which can reduce overall concentrations over time. Additionally, it references California's regulatory actions regarding ozone-producing air purifiers.

PREREQUISITES
  • Understanding of ozone chemistry, specifically O3 molar mass (48 g/mol)
  • Basic knowledge of air density at 20 degrees Celsius (1.2 kg/m3)
  • Familiarity with unit conversions, particularly mg/hr to moles
  • Awareness of air quality standards, specifically the ozone safety threshold (50 ppb)
NEXT STEPS
  • Research the effects of ozone on indoor air quality and health
  • Learn about the natural dissipation processes of ozone in indoor environments
  • Investigate California's regulations on air purifiers and their implications
  • Explore alternative air purification technologies that do not produce ozone
USEFUL FOR

This discussion is beneficial for environmental scientists, air quality researchers, and consumers considering the use of ozone-producing air purifiers. It provides insights into the potential risks associated with ozone exposure and regulatory measures in place to protect public health.

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Hi! I'm terrible at this sort of thing so came to this forum for help. I'm trying to figure out how much ozone an air purifier will throw into my indoor air. The unit produces 360 mg/hr. My space is 2500 square feet. Ceilings are 10 feet high.

The threshold for ozone safety is 50 ppb.

Can anyone help me figure out how long I can run the unit before I reach the 50 ppb threshold?
 
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ppb is parts per billion, right?
I can walk through the process, but I cannot vouch for how accurate the approximations are.

According to Wikipedia, air at 20 degrees Celsius is about 1.2 kg per m^3.
And molar mass of dry air is 0.0289644 kg/mol. This means that
## \frac{1.2}{0.0289644} ## should approximate the number of molecules (in moles) in a cubic meter.
Using the rough conversion of 3m ##\approx## 10ft, your space is about 15mx15mx3m ##\approx## 675 cubic meters.
As a rough estimate, I would use
## 675 \frac{1.2}{0.0289644} = 27965 \approx 28000 ##
moles of air particles in your home.
Remember that there may already be some ozone in your air.

Next, we will convert 360mg/hour into particles per hour.
Ozone is O_3, which has molar mass of 16*3 = 48g/mol. If you are outputting 360 mg per hour, then that is
## \frac{360 mg }{48000mg} = .0075## moles per hour.

dividing the moles of ozone by the moles of air, you get
## \frac{7.5 x 10^{-3} }{ 2.8 x 10^4 } = 2.7 x 10^{-7}##
Converting to parts per billion, you want the exponent to be -9, so multiply by 100 to get about 270 ppb.

Lastly, you should consider how much ozone will dissipate and/or convert by natural processes back to oxygen. This rate of change will work against the buildup of ozone in your home.

Finally, as I was looking for additional conversions, I found a link to California's recent action on ozone-producing air purifiers. It looks like there is good information at their web page
https://www.arb.ca.gov/research/indoor/aircleaners/consumers.htm
 
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Wow! I'm glad I came here for help. Thank you RUber!

So, it would produce 270 ppb in an hour?
 
That's what I get based on the conversions and approximations I used.
It seems high, but I think that is why recently many consumer groups have advocated against ozone-producing air purifiers -- because they replace one type of pollutant with another.
Ozone does naturally dissipate, so if you use it continuously for 100 hours, you would have significantly less than 27000ppb in your home.
That is the extent of my knowledge on the matter, though. I am simply a mathematician, not an environmental (air quality) scientist.