*2.1.3 MQ-135(NOx and SPM sensor)*

The calibrated MQ-135 air quality sensor is used for detecting an extensive series of parameters, including NH3, NOx, alcohol, benzene, SPM and CO2. But, it shows high sensitivity for NOx and SPM [9]. Its characteristics curve is shown in **Figures 7** and **8**.

*Design and Development of Air Quality Monitoring System for Solapur City Using Smart… DOI: http://dx.doi.org/10.5772/intechopen.98755*

**Figure 5.** *LM-35 characteristics curve.*

**Figure 6.** *Arduino interfacing.*

#### *2.1.4 Atmega 328 (controlling unit)*

The Atmega 328 is an entrenched board having inbuilt USB proficiency. The minuscule and user approachable temperament makes it finer than other sophisticated microcontrollers. These microcontrollers encompass additional inbuilt amenities like +5 V, analog and digital pins. It does not comprise on board power jack. Owing to the auto switching potential of the microcontroller, no exterior power jumper is necessary [10]. It posses assorted on board pins and have advanced features as follows:


**Figure 7**. *Characteristics curve of MQ-135.*

**Figure 9.** *Arduino nano pin configurations.*

*Design and Development of Air Quality Monitoring System for Solapur City Using Smart… DOI: http://dx.doi.org/10.5772/intechopen.98755*

Consequently, the WSN nodes are premeditated using arduino nanomicrocontroller. An actual pin specification of arduino nano is depicted in **Figure 9**.
