# Development of an Automatic Low-Cost Air Quality Control System: A Radon Application
The current work builds on the previous design and implements the capability of automatically controlling ventilation systems based on the air quality predictions. To achieve this, in this work, we developed control devices that could be attached to an existing ventilation system and can receive commands from the server. This work's main goal was not only to develop an automatic air quality control system but to develop an algorithm intended to control, by activating the airflow system, some of the variables the system uses to measure air quality and test the best parameters for the algorithm. When processing the data, we need to choose which variables the prediction algorithm uses to decide if the airflow is activated. In this work, we present the results of using the system to control the radon level automatically. We chose to use the radon level to assess the system viability and stability due to high radon concentrations being a direct health risk that has a more immediate impact than other environmental measures such as temperature or humidity. To evaluate the obtained results, we took into account other variables that do affect the previously mentioned issues: energy efficiency, thermal comfort, noise pollution and generally, indoor environmental quality. Concerning the international regulatory state of radon control, public health organizations and governments at all levels are currently implementing different recommendations, guides, and other normative to regulate this issue and developing programs that involve both notions towards a safer quality of life for citizens while maintaining overall growth. Generally, it has been slowly defined during the past few decades, strongly in first world-countries with higher radon concentration issues, but overall it is still an on-going task [34,35]. At a national level, Spain became part of the European Atomic Energy Community (Euratom) in 1985 after the signing of the Madrid Treaty, with the main objective of raising the living standard in the Member States and establishing conditions that would contribute to the creation and safe development of nuclear industries. In 1990, The European Commission published its Recommendation 90/143/Euratom [36], relative to the protection of the population against the dangers of exposure to radon inside buildings, leading the way towards its proper regulation. In 2018, the European Directive of 2013 [37] came into force, establishing safety standards for protection against ionizing radiation: radon levels in the air may not exceed 300 Bq/m\({}^{3}\) as the annual average concentration of activity in the air. Meanwhile, other countries are already working with lower levels: 100 Bq/m\({}^{3}\) in the UK, 200 in Ireland, 150 in the USA. According to the WHO, the risk of cancer grows 16% with each increment of 100 Bq/m\({}^{3}\). The Technical Building Code, which constitutes the main set of regulations of the construction of buildings in Spain since 2006, has not included any updates concerning radon until very recently, despite the above mentioned regulation. In December of 2019, the Council of Ministers finally approved a Royal Decree to Modify the Technical Building Code [38], which will now include a new section of the \"Basic Health Document\" dedicated to the protection of buildings against exposure to radon gas [39]. This section contains the regulatory measures to limit radon's penetration into buildings based on the radon risk of the municipality in which they are located. In each of these areas, different construction formulas must be implemented to avoid this gas's immission in new constructions. The publication of a new Instruction IS-33 of the Nuclear Safety Council is also expected, which would provide new aspects of radiological criteria for protection against exposure to natural radiation.