MQ135 Air Quality Sensor Harmful Gas Detection

The MQ135 Air Quality Sensor is a gas sensor for detecting harmful gases and general air pollution. It responds to ammonia (NH3), nitrogen oxides (NOx), alcohol, benzene, smoke and carbon dioxide (CO2), and its resistance drops as the gas concentration rises. With an Arduino or ESP32 it is a popular way to build indoor air quality monitors and ventilation controllers.

MQ135 Air Quality Sensor Specifications

• Sensor: MQ-135 tin dioxide (SnO2) gas sensor
• Detects: NH3, NOx, alcohol, benzene, smoke and CO2
• Heater voltage: 5 V
• Heater resistance: 33 Ω ±5% (about 150 mA at 5 V)
• Heater power: up to about 800 mW
• Output: analog signal that rises as gas concentration rises; module versions also add a digital threshold output
• Preheat: more than 24 hours before first use for stable readings

MQ135 Air Quality Sensor Applications

• Indoor air quality monitors
• Automatic control of ventilation and extractor fans
• Detecting smoke and fumes in workshops and kitchens
• IoT environmental stations with ESP32
• School science and STEM projects

What's in the Box

• 1 × MQ135 air quality sensor

Tip: The heater gets warm and draws about 150 mA, so power it from a solid 5 V supply, not a 3.3 V pin. Let it warm up for a few minutes before each reading. If you read it with an ESP32, use a voltage divider so the analog signal stays below 3.3 V. The MQ135 gives relative readings and is not a calibrated safety alarm.

Orders placed before 14:00 are ready for pickup the same day. Delivery across Lebanon usually takes 1–3 working days.