Currently, the wireless sensor networks are hugely demanded in every field instead of due to its vast applications specifically for the security purposes and for monitoring. Basically, the wireless sensor networks are the infrastructure less networks which consist of mobile nodes that have memory for storage and to process the data. There can be small networks or large networks. These days, due to the advancement of technology, several kinds of new challenges even though the technology change

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... fe, offering a lot of facilities. The most common problem in the atmosphere is the pollution and air pollution is hazardous for health. The wireless sensor networks (WSNs) are utilized for controlling and managing the air pollution. In WSN, the routing protocols are playing out a major role for the best communication of nodes to enhance the security in the network. In the present research work, the classification of different routing protocols is discussed in detail. The major routing protocols are SPIN, DD, RR, LEACH, PEGASIS, TEEN, APTEEN, HEED, GAF and so on. All these routing protocol come under different categories as namely as flat, hierarchical, location based and the hybrid. Additionally, a comparison is made to clarify different routing protocols with its relevant merits, demerits and classification. In this way, the current research is being more fascinating to work in the monitoring applications such as for the air pollution monitoring systems.