## 2 Related Work
The _iAQ+_ solution proposes a valuable instrument for enhanced living environments in smart cities. The advantages for well-being, comfort and productivity of healthy IAQ levels can be enhanced by reducing the pollutant concentration when the ventilation is still unchanged [44]. Consequently, the authors propose a wireless system which incorporates an ESP8266 module which performs the IEEE 802.11 b/g/n networking protocol. The ESP8266 support built-in Wi-Fi technology, therefore, this module is used not only as a processing unit but also for data transmission. For data consulting, this solution uses a smartphone application developed using SWIFT language for the iOS operating system (Figure 1). Taking into account the IAQ influence on health, the development of a low-cost, open-source supervision system is a trending idea. Therefore, several monitoring solutions have been created [45; 46; 47; 48; 49; 50; 51; 52]. Regarding the quality and important contribution of the referred solutions, a review of these studies is presented in Table 1.  
_Proposed iAQ+ Management System_  
Considering the importance of developing a cost-effective system, only the Bosch BME680 sensor was chosen. This sensor was selected since it is an integrated environmental sensor produced particularly for portable applications and wearables where dimension and low power consumption \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Authors** & **MCU** & **Sensors** & **Architecture** & **Low Cost** & **Open-Source** & **Connectivity** & **Data Access** & **Easy Installation** & **Notifications** \\ \hline [PERSON]. [PERSON] and A. & Raspberry & & & & & & & & \\ Pandharne [45] & PI & & & & & & & & \\ \hline F. [PERSON] et al. & Arduino & & & & & & & & \\ \hline
[46] & UNO & & & & & & & & \\ \hline [PERSON] & & & & & & & & & \\ \hline F. [PERSON] et al. & Arduino & & & & & & & & \\ \hline [PERSON] et al. & Arduino & & & & & & & & \\ \hline [PERSON] et al. & Arduino & & & & & & & & \\ \hline [PERSON] et al. & Arduino & & & & & & & & \\ \hline [PERSON] et al. & Arduino & & & & & & & & \\ \hline [PERSON] & & & & & & & & & \\ \hline et al. [49] & Arduino & & & & & & & & \\ \hline [PERSON] et al. & TI & & & & & & & & \\ \hline et al. [50] & MSP40 & & & & & & & & \\ \hline [PERSON] and K. & TI & & & & & & & & \\ [PERSON] [51] & MSP40 & & & & & & & & \\ \hline  & & & & & & & & & \\ \hline  & & & & & & & & & \\ \hline  & & & & & & & & & \\ \hline  & & & & & & & & & \\ \hline  & & & & & & & & & \\ \hline \hline \end{tabular}
\begin{tabular}{c} \hline MCU: microcontroller; \(\surd\): apply; \(\times\): not apply.  
\end{table} 
Table 1: A summary comparison of real-time IAQ monitoring studies. Figure 1: _iAQ+_ architecture. are essential requirements. This sensor provides temperature, relative humidity, barometric pressure and qualitative air quality, the main parameters that should be supervised for both school and laboratory scenarios. The proposed system is composed of a hardware prototype for environmental data acquisition and a Web portal and mobile application compatible for data access (Figure 1). The _iAQ+_ is based on open-source technologies and is a totality Wi-Fi solution with various benefits when related to current solutions, such as its modularity, scalability, low-cost, real-time notifications and easy installation. The data collected is stored in a SQL Server database management system and a smartphone application or a Web portal can be used for data consulting. The _iAQ+_ incorporates the ESP8266 microcontroller with built-in Wi-Fi communication technology and has been tested in the context of infrared thermography experiments. Taking into consideration the SQL Server native.NET framework integration feature, this database management system was chosen. Furthermore, the SQL Server incorporates several advantages such as data-recovery features, professional management utilities and built-in data compression and data encryption features.