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14 Apr, 4 tweets, 3 min read
Indoor PM @theNASEM workshop: @ChemDelphine Deposition of particles is the most poorly understood component both indoors and outdoors. Outdoors PM lifetime is about a week. PM across the US has been decreasing in general, except for wildfires.
Indoor PM @theNASEM workshop: @ChemDelphine: PM ages within hours of wildfire emission. Gases from wildfires can oxidize then condense onto PM. Drivers of oxidation potential (i.e. vehicles wear/SOA) of aerosol varies geographically.
Indoor PM @theNASEM workshop: @ChemDelphine: Indoor PM time frame is minute to hours, instead of days of outdoors. Chemicals can evaporate from PM into the gas phase once move indoors. Especially when heating in winter. In summer, chemicals condense on outdoor PM once indoors.
Indoor PM @theNASEM workshop: @ChemDelphine: Composition of particles matter. Phthalates partition on to particles dependent upon the make up of the particles. Third hand smoke chemicals partitions differently to different particulate matter.

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More from @Poppendieck

Dustin Poppendieck Profile picture
14 Apr
Indoor PM @theNASEM workshop: @linseymarr: Absolute humidity total amount of water in a sponge, relatively humidity is fraction of water it can hold. Sponge size depends on temperature. Absolute indoor humidity tracks outdoor, except when air conditioning. Relative does not.
Indoor PM @theNASEM workshop: @linseymarr: Who fills humidifiers with distilled water? (I DO!). Ultrasonic humidifiers produce a distribution of particles, number concentrations depends on water chemistry. Much of the mass is smaller than 0.3 microns.
Indoor PM @theNASEM workshop: @linseymarr: Which is lower than consumer grade PM sensors can see. Relatively humidity (RH) is important as it controls evaporation. Below 80% RH things aerosols shrink to similar size, but the rate is RH dependent.
Read 5 tweets
Dustin Poppendieck Profile picture
14 Apr
Indoor PM @theNASEM workshop: @marinavance: Indoor sources can impact outdoor ambient air. PM2.5 and larger concentrations increased when house is ventilated, but cooking and cleaning increased PM concentrations an order of magnitude higher.
Indoor PM @theNASEM workshop: @marinavance: Notes that the "Brussel sprouts were nicely cooked in the oven." Points out that PM0.1 concentrations highest during cooking, but this size is below what consumer grade PM sensors can see.
Indoor PM @theNASEM workshop: @marinavance: Cooking heat source is likely responsible for PM number concentrations, while the food is responsible for the mass concentration. Plasticizers and siloxanes are seen in on particles when cooking.
Read 5 tweets
Dustin Poppendieck Profile picture
28 Feb
Using CO2 as a ventilation clue!

Welcome to a long thread about seven complications related to using CO2 for indoor ventilation measurements...

It be fun... really!

1/
COMPLICATION #1. CO2 does NOT equal IAQ (Indoor air quality). CO2 is a good surrogate for human emissions. But in indoor spaces we have emissions from building materials, furniture, cleaning agents, and cooking. 2/
COMPLICATION #1 (Cont). In addition to the 1,000’s of chemical from those sources we also have indoor chemistry happening in the air. So CO2 is a good measure of required ventilation only in places with lots of people (classrooms, gyms) where human emissions dominate. 3/
Read 29 tweets
Dustin Poppendieck Profile picture
25 Feb
Consumer grade indoor air quality sensors, what are they good for? A thread... 1/7
When I was in highschool I walked to school. In the winter had the choice to walk ~1 km around a small lake or ~0.5 km across the lake. The big unknown was always was the ice thick enough to make sure I did not fall in. 2/7
I had several sources of data I could use to help me make that decision. 1) The imediate temperature, 2) the historical temperature, 3) if there were cars on the lake (ice fishing). 3/7
Read 7 tweets
Dustin Poppendieck Profile picture
19 Oct 20
Air change rate is the rate of air ENTERING (not leaving) a room divided by the volume of the room. Why is this important? 1/n
Because of mixing it takes up to 3/(air change rate) for 95% of the air in a room to exit the room due to mixing. 2/n
So if the air change rate is 6/hour, it will take up to 0.5 hours to remove 95% of the air originally present. 3/n
Read 4 tweets
Dustin Poppendieck Profile picture
14 Oct 20
Are you opening windows and using fans to move air into or out of a room? 1) Try to isolate the fan so it doesn't capture air it just blew. 2) Open a second door or window so the air has somewhere to go/come from other than cause condensation in walls (mold). 1/6
Typical $20 box fans claim to move 2,000 cfm (cubic feet per minute) on a high setting. A typical class room around 8,000 cubic feet. This equates to an air change rate of about 15 per hour, or taking 12 minutes for 95% of the original air in a classroom to leave. 2/6
The high setting is rather loud and flows are optimistic. @JohnSemmelhack showed yesterday numbers from 1200-1400 cfm with no filter. If we assume the flow (no filter) is about 1,000 cfm then the air change rate is 7 per hour, or about 25 min to change 95% of class air. 3/6
Read 6 tweets

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