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0.35 kg of particulate contamination removed per day; you rounded incorrectly, but the rest of your math is right. There's the issue that it's probably removing nearly all of the particulates from the air it actually processes, say over 90%, which works out to 2.1 kg. It doesn't reduce the PM2.5 level in the area by 90%, but only by 15%, because it's only able to process some 16% of the air in its area during whatever the relevant time interval is, which seems like a good match to your 10%-per-day. However, you got the volume of that area wrong: it's 10⁹ m³, not 10⁸ m³. That suggests that the natural lifetime of PM2.5 particulates is closer to a week than a day. As for jhugg's question about how the filters are cleaned, a common way to remove particulates from flue gas or indoor spaces is using electrostatic precipitators, which are flat plates at a high voltage. The voltage sticks the particulates to the plates, and when the coating is thick enough, you close the valves to stop the gas flow and vibrate the plates to unstick the dust, and it falls out the bottom of the filter into a bucket (or, say, a truck). Other systems clean the plates with water (either spray or immersion) and possibly soap or lye. |
That's what I get for interweaving a mantissa of 10 with scientific notation! Too late to edit now, but people should see this comment thread.