Indoor air quality dataset from a low-cost ESP32 + MP-135 + DHT22 monitor (Dhaka, October–November 2026)

46,897 readings (one every 30 s, 16 October – 1 November 2026) from a low-cost indoor air monitor in Dhaka, Bangladesh, built from an ESP32, a Winsen MP-135 metal-oxide gas sensor and a DHT22 temperature/humidity sensor. Includes raw ADC values, sensor resistance, a humidity- and temperature-compensated ratio, a relative Pollution Index (100 = the room's usual level; not an official AQI), four air-quality classes, 2/5/10-minute-ahead class targets and a time-based calibration/development/test split. The training notebook and the ESP32 firmware with the on-device TinyML forecasting model are included.