MQ135 Air Quality Sensor will be a good assistant and provide useful information about the surrounding air. Sensitive material of this sensor is SnO2, which with lower conductivity in clean air. When the sensor senses combustible gas, the conductivity of the sensor and gas concentrations will increase. It is better to use a simple electro circuit and convert the change of conductivity to correspond output signal of gas concentration. MQ135 gas sensor has high sensitivity to Ammonia, Sulfide and Benze steam. It is also sensitive to smoke and other harmful gases. MQ135 Air Quality Sensor is a low cost and suitable for different applications. It can be used for the Surrounding environment noxious gas detection device. It can measure ammonia, aromatics, sulfur, benzene vapor and other harmful gases/smoke that its tested concentration range is: 10 to 1000ppm. In order to use it with Arduino, connect DO to any digital pin (if you want it in digital input) or connect AO at analog pin (if you want it in analog input).

Air quality sensor is for detecting a wide range of gases, including NH3, NOx, alcohol, benzene, smoke and CO2. Ideal for use in office or factory, simple drive and monitoring circuit.

Features
Model: MQ135
Working Voltage: 5V
Working Current: 150mA
DOUT: TTL output
AOUT: Analog output
Interface: Analog, TTL
Preheat Time: Over 20s
Pin Number: 4 Pins
Size: 32mm x 22m x 27mm