SEN0471 and SEN0472

I am using four gas sensors (SEN0472, SEN0466, SEN0471, SEN0470), PM sensor (SEN0460), Temperature & Humidity Sensor(SEN027).All the sensors have been integrated with either Arduino uno or Arduino mega(any one at a time) using I2C communication protocol. All the components are being operated with 5V power supply except the main controller board(Arduino mega/Arduino mega). I am trying to print the sensed data on serial monitor as well as on an OLED display in a continuous mode. The repetition of print of each sensor's output is about 15second gap and the gap between print of consecutive two sensors is about 2sec. 

Now, the problems have been listed down.

1. The values given by the NO2(SEN0471), O3(SEN0472) and SO2(SEN0470) seem not to be real values of the ambient air (Experimenting in our lab environment)

2. After about 2-3 hours either NO2 gas sensor(SEN0471) or  O3(SEN0472) or both the sensors are giving abrupt values, though the values corresponding to  each gas is a fixed number.
For reference I am attaching herewith a few snapshots of the serial print