Use these sources:
https://arxiv.org/pdf/1005.1737.pdf
https://pdfs.semanticscholar.org/4e9d/c73e2b137a5360ebae608c56877a6b725b9b.pdf
https://www.researchgate.net/publication/269311725_Wireless_Sensor_Network-based_air_quality_monitoring_system
https://www.ijcnis.org/index.php/ijcnis/article/viewFile/2708/248
https://ieeexplore.ieee.org/document/6137040