ChemAir said:How are you measuring your pm2.5 particulates?
jrmichler said:Your doors and windows may be closed, but your house is always leaking air. Air leaks out, and for every cubic foot that leaks out, an equal cubic foot leaks in. Older house leak a lot, new houses in cold climates have to meet codes that require less leakage. Good search terms to start with are home air changes per hour or home air leakage.
Since air is leaking in, particulates floating in that air are coming with it. The rate of PM2.5 rise is a measure of the leakiness of your house.
Cutter Ketch said:I would think a more likely explanation for variations on the few hours scale would be the dust on the surfaces of the interior of your home. Even a clean home can have milligrams of dust per square meter. My house is probably closer to grams per square meter. A small fraction of this dust is constantly being kicked up by air currents and settling back down on surfaces. The surfaces act as a semi-infinite source of airborne particles produced at a semi-constant rate (proportional to the quantity of dust, but that will only change slowly through the process of filtering the air). The rate at which the dust settles is proportional to the concentration of airborne particles. The concentration in the air rises until the rate of settling out equals the rate of generation. When you add a filter the rate of removal is still proportional to the airborne concentration, but the proportionality is now much larger. The rate of generation equals the rate of removal at a much lower airborne concentration. When you turn the filter off the concentration quickly (and 2 hours is quickly) rises to the previous equilibrium.
Over a longer time the filter will reduce the total available dust, but your coming and going not to mention air exchange with the outside will also be increasing the amount of dust. How often you dust is another critical factor. So there is a longer term equilibrium being generated by exchange of dust with the outside world which is most of what was discussed above. However I think the two hour time scale you are describing is going to be about what is already inside the home.
Diffusion behavior refers to the movement of particles from an area of high concentration to an area of low concentration. This process occurs naturally and is driven by the random motion of particles.
The diffusion behavior of particulates can be affected by several factors, including temperature, concentration gradient, particle size, and the medium through which the particles are diffusing.
The rate of diffusion can be measured by observing the change in concentration over time. This can be done using techniques such as spectrophotometry or by tracking the movement of particles under a microscope.
Understanding diffusion behavior is important in many scientific fields, including chemistry, biology, and environmental science. It can help us understand how substances move and interact in various systems, and it has practical applications in industries such as pharmaceuticals and food production.
Yes, diffusion behavior can be manipulated through various methods such as changing the temperature, concentration, or size of the particles, as well as altering the properties of the medium. This can be useful in controlling the movement of substances in a desired direction or rate.