Abstract: We are going to make an low cost air pollution detector using arduino in which we will monitor the Air Quality and monitor it and it will trigger the alarm when the quality of air goes down beyond certain level, that means when there are the sufficient amount of harmful gases present in the atmosphere sulfur dioxide (SO2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxide (NO). It will show the air quality in PPM on the LCD. Quality Assessment will be performed by low cost smart sensors that will be able to collect accurately several quality parameters such as temperature, Physical and chemical etc.The traditional method of testing is to collect samples manually and then send them to laboratory for analysis. However, it has been unable to meet the demands of the quality monitoring today. So, a system of Monitoring quality will be developed. The system consists of Temperature sensor of quality testing, single-chip microcontroller data acquisition module, monitoring center and other accessories. Air quality & Temperature of are automatically detected under the control of single chip microcontroller all day. Then processes and analyzes them. If the quality is abnormal, it will alert the public through SMS ALERT at the same time. It is convenient for management to take corresponding measures timely and be able to detect realtime situation of air quality. The main focus is on to construct a low-cost sensor system for real time monitoring of the air quality in environment.Previously we have built the LPG detector using MQ6 sensor and Smoke detector using MQ2 sensor but this time we have used MQ9 sensor which is the best choice for monitoring of the Air Quality as it can detects the most harmful gases and also measure the amount accurately. In this project, you can monitor the pollution level from anywhere using your computer or mobile. We can install this system anywhere as per our requirement and can also trigger some device when pollution goes beyond some level, like it can switch on the Exhaust fan or send SMS alert to the users.Keywords: Low Cost Sensor, Air Pollution Monitoring, Sensors, GSM SIM Module.