Let's start by clarifying this thread will be about mechanical filtration where the particles are removed via a physical process.
This thread is not about filtration technologies that rely on energy or chemical reactions to remove particles.
2/18
FIT:
Air must go through the filter to be effective. Whether on your face (N95s) or in a duct (MERV13) if there is a bad fit a majority of the air will not go through the filter.
Just like water finding the easiest path down hill,
3/18
#HBA2021. @anna_s_young. Sampled 231 office workers with wrist silicon wrist bands (only worn at the office) in US, UK, India and China. Analyzed for SVOC in 100 wrist bands by Heather Stapleton's group.
Exposure to chemical classes varied by location.
US workers exposed to PCBs that were banned 40 years ago. Exposures to PCBs in India higher. Paint likely a PCB source.
Brominated flame retardant higher in US and UK compared it China and India. People still exposed to flame retardants that have been banned over 10 years.
#HBA2021 - Antonios Tasoglou. Investigated electronic air cleaners using real time instrumentation. Used 30 m3 chamber, 25C and 50%. Limonene, formaldehyde and toluene as challenge gases. 1/5
Analyzed with ozone, PTRMS, DNPH, Tenax, particle counts as analysis methods. Example electronic cleaner with UVC/TiO2/HEPA/carbon filter. Limonene and toluene decreased to zero within an hour, formaldehyde did not decrease below 40 ppb after four hours. 2/5
Loss rates for limonene and toluene were 4-5/h. For formaldehyde the loss rate was only 0.7/h, as it is an oxidation product of toluene and limonene. 3/5
Uncertainty in using CO2 for ventilation clues in Classrooms.
A LONG Thread... 1/
Short version:
High CO2: REAL BAD.
Low CO2: Meh...
In Between: Who knows... better get filtering.
2/
First lets talk about short versus long range transmission.
1) The highest COVID transmission risk is short range where the aerosols are highest in concentration. Well fitting masks and distancing are the best defense. 3/
How do air change rate, ventilation rate and maximum carbon dioxide concentration in a room relate? Its complicated. But in general they relate like this:*
*Example classroom, the shape remains the same, while actual y-axis value change with room/age/activity. 1/7
If the maximum concentration in a room is above ~2,000 ppm we know that the ventilation rate/air change is BAD (flat part of curve). Small increases in ventilation will drop the carbon dioxide concentration quickly. 2/7
If the maximum concentration in a room is below 700 ppm we know the ventilation probably good (steep part of curve). Big increases in ventilation will only slightly drop the carbon dioxide concentration. 3/7