Residents can't tell if their own room is safe when Bangkok's PM2.5 spikes, even with AC and purifiers
One resident measured indoor PM2.5 of 25 to 33 under central AC while outdoor PM2.5 read 37, and could only get under 8 by turning the AC off and running a purifier. Commenters disagree on whether building AC pulls in outside air. In a January thread residents post an AQI of 181 and say it feels like this half the year.
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5 ways to tackle it
Hardware and sensors
Two-Point Probe: PM2.5 at the AC vent and the room, a light shows where it leaks
An ESP32 with two PM2.5 sensors measures the air coming out of the AC vent and the air in the middle of the room. A small LED ring turns red when the vent air is dirtier than the room, which answers the 'does central AC pull in outside air' argument with numbers.
Build with ESP32, 2x PMS5003 sensors, LED ring, phone web page
Hardware and sensors
Purifier Plug: a smart plug that runs your purifier only when the room needs it
An ESP32 plug watches indoor PM2.5 and switches the purifier on above 15 and off below 8, and refuses to run it with the door open. It logs hours and kWh, so people stop guessing whether it is worth the electricity.
Build with ESP32, relay module, PMS5003, Wi-Fi, simple web dashboard
Camera and vision
Filter Photo: photograph the filter against a gray card and learn if it is done
The resident photographs the purifier or AC filter next to a printed gray reference card. Claude vision judges how clogged it is from the color against the card and says 'swap now', 'two more weeks' or 'fine'.
Build with Claude vision, printed gray reference card, PWA
Data and maps
Window Hour: tells you the exact hour today when outside air beats your room
It combines your probe reading with the Air4Thai forecast and calls the best hour to open a window, cook or exercise indoors. It pushes a one line answer to the phone.
Build with Air4Thai API, Open-Meteo, Claude, push notification
Web portal
Cube Builder: enter your room size and print a cutting template for a DIY box-fan purifier
You enter room size and budget. The tool prints a template, a Thai shopping list for a box fan and four filters, and the cost against a store-bought purifier. A Corsi-Rosenthal cube can cost a fraction of a branded unit.
Build with Next.js, Claude, PDF template generator
What people reported
Resident logs indoor PM2.5 25 to 33 under central AC with outdoor 37, only below 8 with AC off and purifier on. Replies split on whether AC brings in outside air, advise asking building managers about filter cleaning.
reddit.comJanuary post of 181 AQI in Bangkok. Replies: black phlegm in the morning, 'feels like this half the year', one just bought a big purifier.
reddit.com