Air quality monitoring and conditioning is the second most important task that telescope dome automation system AS2 performs. This set of functions has been designed with significant flexibility in mind, as details of dome construction and location, as well as types of scientific equipment they contain vary enormously. But despite the plethora of possibilities, two crucial tasks presented to dome air conditioning subsystem are practically always the same: protecting sensitive scientific equipment from damage that might be caused by freezing, dew formation, overheating etc, and maximizing time available for scientific work.

Because air conditioning can be crucial for equipment maintenance, AS2 provides two levels of its implementation:

ETH-2 is an ELM-4 compatible device able to operate both as a part of the more complex dome automation system, or autonomously. In its autonomous mode, ETH-2 collects meteorological data from its sensor inputs and regulates heaters, heat pumps or other air conditioning devices with the aim of maintaining air temperature and humidity within the preset range.

While ETH-2 processing power is limited in comparison with typical PC capabilities, the advantage of this approach is higher reliability of air conditioning as the process depends neither on ELM-4 data bus availability, nor on PC, Windows^TM or grid power supply correct operation. Although this method might appear basic, it is able not simply to maintain optimal dome temperature during the day targeting the predicted air temperature for the following night, but as well to keep telescope optical surfaces free from dew formation.

In case that basic air conditioning does not suffice, AS2 permits observatory operators to construct arbitrarily complex control algorithms. These are able to utilise large number of sensor data that AS2 is able to collect via its input modules, as well as large number of control outputs that can be added to the system.