The air we breathe indoors

In the second installment of the FairAir talk series, Professor Peter DeCarlo of Johns Hopkins University discusses the origin of particles indoors as they relate to indoor air quality in his talk, “The air we breathe indoors”.

Missed the talk? You can view the recording HERE.


Questions answered during the Q&A session:

Q: Can COVID-19 aerosols or droplets attach to air particles like PM 2.5,10 or other particle pollution? If COVID-19 can attach to particles what level of public health danger does this create and how long might these particles be viable and a health danger?

A: (Peter DeCarlo) So when particles attached to each other what we typically see is really small particles doing that to larger particles. COVID particles by themselves are large enough that they’re probably not going to attach to other PM 2.5 particles, but they’ll be in the air at the same time.  I think there have been some studies showing that higher levels of PM 2.5 and higher levels of PM10 can be associated with worse impacts or higher transmission rates of COCID. It’s not clear what the mechanism is for that, and it may be due to the PM2.5 and 10  being more of respiratory irritants and then the COVID coming in and exacerbating those problems but I don’t think attachment of those two things is really the mechanism by which it is getting into the body. I think it just gets in because it’s big enough to do it by itself.


Q: I have a Harmon Pellet Stove equipped with a Catalytic Converter; yet I see no instructions from the manufacturer and/or dealer on how to determine if the converter still works. Any ideas of how to check its effectiveness after 10 years of use.

A: (Peter DeCarlo ) I don’t have a lot of experience with that, I mean catalytic converters are from a science perspective and an engineering perspective they’re supposed to essentially last forever.  They provide a surface for additional oxidation reactions to occur.  So what they are intended to do is anything that doesn’t burn fully in the pellet stove should further burn in a sense, on the surfaces of the catalytic converter.  That being said, I know that when we were doing measurements in Switzerland with a vehicle, we were just idling the vehicle over and over and over and over again. We eventually fouled our catalytic converter.  It didn’t work properly, because it never got up to the temperature it needed to get to, to work efficiently. We drove it on the highway at some point and it burned off all the stuff that had collected on the surface and it started to work again, and so I think, as long as you’re using your pellet stove at its normal operating parameters, the catalytic converter should continue to work properly. I think it’s probably a safe bet that it’s working at some reasonable efficiency at this point.


Q: Any sense of how outdoor PM from other circumpolar regions is circulating around the circumpolar north? How much of our outdoor PM is “locally produced”?

A: (Peter DeCarlo )Trans boundary air pollution is an issue at all latitudes.  Certainly in the polar regions in the in the winter time when it’s dark you can get air transported from Russia and from Canada coming back around.  My sense looking at this is this is that generally the concentrations in Fairbanks if you’re not burning a bunch of wood are really low.  In general, you’re not getting a whole lot of contribution from other places, and the vast majority is going to be locally produced.  You could probably get a far enough out of Fairbanks, away from where people live and make measurements and you would see very, very, very pristine condition. I think just that gradient from Fairbanks to 10 miles away would give you an indication of how much is really just locally produced.


Q: Our major electric company in Fairbanks burns diesel at some plants and coal at others. The exhaust lingers in the air during the cold times in winter. What does that mean for the particulate matter levels? Can you point me towards references that can better inform what implications coal and diesel burning may have?

A: (Pete DeCarlo) In general, the strategy for air pollution has been to build stacks so if you exhaust you’re burning at a much higher level, it gives it a chance to disperse before it gets back down to ground level where we are breathing.  In the wintertime we have a lot of inversion layers.  Fairbanks has some pretty strong and inversions, and so a lot of times what happens is that those emissions are actually admitted above that inversion layer and they don’t make it back down as frequently to the surface, as they would in other seasons.  That being said, they can obviously still impact air quality and it depends really on the meteorology at the time.

It’s something that we are certain is certainly on our radar, and it’s something that we want to investigate with all of the expensive instrumentation that we’re all bringing up next winter.  I want to say, this is a to-be-determined based on some of the studies that we’re planning to do currently.

(Bill Simpson) I just want to reinforce that this study will be really nice for getting experts like Pete and others who have really state of the art instrumentation that can more finally separate what’s in the particles than the routine measurements that were done. I think we’re going to learn a lot more about that because Pete will be able to detect more tracers.  There was also a question about coal, I think the question was really about an indoor coal stove and what particles might come into a house and we may or may not be able to research that depending on whether the house we rent has a coal stove.  Nonetheless, do you know good tracers for coal that could measure both outside and inside air to see what influences coal burning might have?

(Peter DeCarl) My general recommendation is try not to burn coal indoors if you don’t have to. I understand that that’s not always possible.  Depending of the quality of the coal you are burning, there will be variations in the level of tracer that you might expect. Coal has some level of sulfur in it.  My group has made measurements in Nepal, where coal is heavily used in an industry and there’s no after treatment of that. What you see with cold direct emissions is a lot of sulfate or sulfur in the particles so that’s something that we would see.  And if we’re doing tests in a house next year where there is a coal stove, we could actually make measurements directly of what’s being emitted and look directly for those chemical signatures, and look to see if the same signatures in the outdoor air are the ones we see in the indoor air. In Nepal, we did identify a couple tracer species in our in our data set that were linked very strongly to that coal burning from the brick kilns in that region.


Q: Do passenger airplanes have five air changes per hour?

A: (Peter DeCarlo) They do more. The biggest danger of air travel is probably not the airplane itself because the airplanes have very, very good error handling units. They’ve had to for a very long time.  They have Hepa filtered air at about 10 to 12 interchanges per hour, which is two to two and a half times what’s recommended.  The biggest danger is actually probably going to be in the airports themselves when you don’t have as much air change and you’re bumping into more and more people.


Q: What effect does using a wood stove have in indoor air quality?

A: (Peter DeCarlo) Every wood stove and every wood stove installation is unique.  Asking questions like, does it have a catalytic converter, how leaky is the wood stove, and how leaky is the exhaust from the wood stove? If you’re getting a little bit of smoke penetrating into the indoor environment, then that’s going to add overall to the concentrations in your house. If you really just getting the heat from the woodstove and all of the smoke is going outside then you’re going to get a little bit coming back in from that outdoor environment, but you’re not going to get as high concentrations indoors.  So it’s a combination of the kind of the technology level of the woodstove, how well it’s been installed, and how leaky or tight everything is that will determine the indoor air quality impact a wood stove it’s going have.


Q: How effective are COVID face-covering masks at blocking PM2.5 particles?

A: (Peter DeCarlo) That’s a great question. Is it a cloth mask, is it can N95, there are so many different permutations of masks that you can’t say with definitive answer how good it is for each thing.  I will say is that masks are really good at filtering your breath going out.  There’s a reason for that.  When it’s really cold outside, you see this cloud of fog coming out of your mouth when you bring out.  Your lungs are moist they’re covered with moisture your body’s at about 100 degrees Fahrenheit.  And so, when that warm moist air comes out and mixes with cold air, you have these rather large droplets.  Those sizes of particles are pretty easily captured even by basic cotton, like three layers of cotton masks, and so that is a protection for other people.  It’s also going to protect to some extent particles coming in, when you breath too. They won’t be as large as the droplets coming out of your breath.  But these masks are certainly a layer of protection that you want to have at all times.  You know if you can get a N95 or equivalent you know that’s going to be something that offers even more protection.  But these masks will filter PM 2.5 in exactly the same way that they filter COVID it’s particle physics and the mask doesn’t know the difference between a COVID particle that’s one and a half micrometres in diameter and an air pollution particle that’s one and a half millimeters in diameter it’s the same physics that’s going to intercept both of those particles.


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