Andrés Gómez Emilsson | Still Smoky Outside @/Andr%C3%A9sG%C3%B3mezEmilsson | Uploaded November 2018 | Updated October 2024, 7 hours ago.
In this video I address two common concerns to the previous video ("It's Smoky Outside" - youtube.com/watch?v=WLotdU2THkU).
1) Some people raised the possibility that the PM2.5 values shown by the measuring devise were meaningless. In particular, they suggested that the devise merely measures airflow. I show this is not the case in the following way:
1.1) When you put it in front of a fan it increases by 75% (from 40 to about 70).
1.2) When you put it on top of the air filter it goes down to about 1.
1.3) The fact that outside is not windy at all and yet the measured values climbed by about 500% (from 40 to 200+).
Clearly high levels of airflow increase the recorded value (I apologize for saying something slightly different earlier, I was holding the devise vertically in front of the fan rather than horizontally and if you do that the measurement doesn't change). But this is tiny compared to the difference in the (non-windy) outside and also compared to the very windy air filter. So no, the devise is measuring particulate matter density, and the air filter is reducing such density by a lot. What remains to be seen is whether the devise is properly calibrated. Maybe a value of 10 is really a value of 15, and a value of 100 is really a value of 150. The tests I ran wouldn't rule that out. However, I can corroborate that the values that national weather stations report for PM2.5 are nearly identical to those I detect outside (usually by +-5).
2) Others wanted to see how the devise would look like on an apartment without a HEPA air filter. This is a bit complicated for the simple reason that outside PM2.5 values shift over the course of several hours, so getting an accurate ratio between outside and inside values is difficult. However:
2.1) A neighbor was kind enough to agree to experiment a bit. At 4:30 or so in the afternoon we had 230 outside and 230 inside of his apartment (remember inside mine the measurement is about 40). The problem, though, is that he had one window very slightly open so of course the inside and outside values would equalize eventually.
2.2) I asked him to close the window down completely and insulate his apartment as much as possible. I then came back an hour later. By then the outside value was about 330 (it increased quite a bit!) but the inside value stayed at around 230.
From this we can say that having all windows closed in a well insulated apartment is likely to keep the PM2.5 values in your apartment steady for a while (at least 1 hour) while outside the values may go up or down. That said, in the long run the values would, I think, equalize. I know this from experience. If I don't turn on my air filter (in non-smoky days) I get nearly identical values inside and outside whether or not my windows are open or closed. It is, in my experience, just a matter of time. Equalization takes a lot longer with windows closed. So if you are afraid of PM2.5 particles (as you should be) and don't have a filter, you should still probably keep all windows closed and only open them when the weather stations say it's safe outside. This, of course, is not an effective strategy if your home is not insulated at all (as is the case in old homes).
-----
Additional Info:
Location: Colma, near San Francisco.
Date: November 11 2018
In this video I address two common concerns to the previous video ("It's Smoky Outside" - youtube.com/watch?v=WLotdU2THkU).
1) Some people raised the possibility that the PM2.5 values shown by the measuring devise were meaningless. In particular, they suggested that the devise merely measures airflow. I show this is not the case in the following way:
1.1) When you put it in front of a fan it increases by 75% (from 40 to about 70).
1.2) When you put it on top of the air filter it goes down to about 1.
1.3) The fact that outside is not windy at all and yet the measured values climbed by about 500% (from 40 to 200+).
Clearly high levels of airflow increase the recorded value (I apologize for saying something slightly different earlier, I was holding the devise vertically in front of the fan rather than horizontally and if you do that the measurement doesn't change). But this is tiny compared to the difference in the (non-windy) outside and also compared to the very windy air filter. So no, the devise is measuring particulate matter density, and the air filter is reducing such density by a lot. What remains to be seen is whether the devise is properly calibrated. Maybe a value of 10 is really a value of 15, and a value of 100 is really a value of 150. The tests I ran wouldn't rule that out. However, I can corroborate that the values that national weather stations report for PM2.5 are nearly identical to those I detect outside (usually by +-5).
2) Others wanted to see how the devise would look like on an apartment without a HEPA air filter. This is a bit complicated for the simple reason that outside PM2.5 values shift over the course of several hours, so getting an accurate ratio between outside and inside values is difficult. However:
2.1) A neighbor was kind enough to agree to experiment a bit. At 4:30 or so in the afternoon we had 230 outside and 230 inside of his apartment (remember inside mine the measurement is about 40). The problem, though, is that he had one window very slightly open so of course the inside and outside values would equalize eventually.
2.2) I asked him to close the window down completely and insulate his apartment as much as possible. I then came back an hour later. By then the outside value was about 330 (it increased quite a bit!) but the inside value stayed at around 230.
From this we can say that having all windows closed in a well insulated apartment is likely to keep the PM2.5 values in your apartment steady for a while (at least 1 hour) while outside the values may go up or down. That said, in the long run the values would, I think, equalize. I know this from experience. If I don't turn on my air filter (in non-smoky days) I get nearly identical values inside and outside whether or not my windows are open or closed. It is, in my experience, just a matter of time. Equalization takes a lot longer with windows closed. So if you are afraid of PM2.5 particles (as you should be) and don't have a filter, you should still probably keep all windows closed and only open them when the weather stations say it's safe outside. This, of course, is not an effective strategy if your home is not insulated at all (as is the case in old homes).
-----
Additional Info:
Location: Colma, near San Francisco.
Date: November 11 2018
