For some time now I've been wondering how well the HEPA filter works. I just answered that question by placing a PurpleAir sensor measuring PM1.0, PM2.5, and PM10 behind the driver seat for a few days and running some test.
The measurements are done using the US EPA Air Quality Index (AQI) units: 0=no pollutants detected, 50=a mediocre big city day, 100=a bad big city day, >150 smoke from fires in the air.
Testing yesterday in Sydney, driving with all windows down: 25. Matches the measurements of other PurpleAir sensors located outside in the area.
Closing all windows, with aircon on auto lowers the AQI to 0 within about 3 minutes.
Driving with windows closed in biohazard mode with outside AQI at 50: 0 on the inside
Driving with windows closed with climate in auto: with outside AQI at 50: 0 on the inside
Getting a passenger to vape their brains out: AQI rushes to >400, and within 2 minutes of stopping, AQI is back to zero.
This could indicate that recirculated cabin air likely is also passed through the HEPA filter. Or the entire cabin air is exchanged with fresh outside air in 2 minutes.
Overall, I'm very impressed, especially given I had assumed this was all smoke and mirrors so to speak, because I can occasionally smell diesel exhaust from the outside when behind a big stinker. Turns out volatile organic compounds (VOCs) tend to be smaller than what the HEPA filter can catch. So we're safe from fine particulate matter in our cars. But not from VOCs.
The measurements are done using the US EPA Air Quality Index (AQI) units: 0=no pollutants detected, 50=a mediocre big city day, 100=a bad big city day, >150 smoke from fires in the air.
Testing yesterday in Sydney, driving with all windows down: 25. Matches the measurements of other PurpleAir sensors located outside in the area.
Closing all windows, with aircon on auto lowers the AQI to 0 within about 3 minutes.
Driving with windows closed in biohazard mode with outside AQI at 50: 0 on the inside
Driving with windows closed with climate in auto: with outside AQI at 50: 0 on the inside
Getting a passenger to vape their brains out: AQI rushes to >400, and within 2 minutes of stopping, AQI is back to zero.
This could indicate that recirculated cabin air likely is also passed through the HEPA filter. Or the entire cabin air is exchanged with fresh outside air in 2 minutes.
Overall, I'm very impressed, especially given I had assumed this was all smoke and mirrors so to speak, because I can occasionally smell diesel exhaust from the outside when behind a big stinker. Turns out volatile organic compounds (VOCs) tend to be smaller than what the HEPA filter can catch. So we're safe from fine particulate matter in our cars. But not from VOCs.
