What environmental condition does a digital monitoring system track?

A digital monitoring system for heating oil tanks is designed primarily to ensure the safety and efficiency of oil storage. The correct option highlights that such systems track temperature and humidity around the tank. Monitoring these specific environmental conditions is crucial as variations can impact the integrity of the tank and the fuel itself. For instance, excessive humidity can lead to condensation inside the tank, potentially causing rust or other forms of corrosion. Meanwhile, maintaining optimal temperature levels helps to prevent the oil from thickening or degrading.

While weather changes, air quality levels, and surrounding vegetation growth are all important environmental factors, they do not directly pertain to the operational safety and effectiveness of heating oil tanks in the same immediate way that monitoring temperature and humidity does. Therefore, tracking these conditions is vital for the preventive measures needed to ensure safe and compliant operation.