## 2 Materials and Methods  
Figure 1 illustrates the scenario for the proposed wireless DYU Air Box for monitoring the environmental conditions of classrooms and visualization on the public Thing5 peak IoT platform through the DYU-802.1X communication network with WPA2 Enterprise security on Da-Yeh University campus. The proposed DYU Air Box is a wireless heterogeneous multi-sensor module which consists of a BH1750 light sensor, a BME680 temperature sensor, an RH and IAQ sensor, an SCD30 CO\({}_{2}\) gas sensor, a PMS7003T dust sensor, and a TIGO ESP32 Wi-Fi device (Lilygo, Hong Kong, China). Firstly, all DYU Air Box modules access the authentication server (AS) through an authenticator for the authentication of an entity through the Enterprise 802.1X communication network. The authenticated DYU Air Box facilitates the forwarding of all environment-monitoring data including AQI value/level, PM\({}_{1.0}\)/\({}_{2.5}\) and CO\({}_{2}\) concentration, brightness, ambient temperature, and RH in classrooms to the public Thing5 peak IoT platform for observation. All stakeholders including students, faculty, staff, alumni, and even students' family can easily visualize the real-time environmental information of classrooms at Da-Yeh University. Especially, all students, faculty, and staff on campus can directly access information through the DYU-802.1X communication network. The design details of the hardware and firmware are described as follows. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Application Scenario**} & \multicolumn{2}{c}{**Sensing Layer**} & \multicolumn{2}{c}{**Communication**} & \multirow{2}{*}{**Application Layer**} & \multirow{2}{*}{**Reference**} \\ \cline{2-2} \cline{5-6}  & & **Processor** & & & \\ \hline \multirow{8}{*}{Industry (metal-processing workplace)} & MQ-2 CO/SO\({}_{2}\) sensors & & & & \\  & CP2Y1010 AUOF dust sensor & & & & \\ \cline{1-1}  & DS18B20 temperature sensor & & & & \\ \cline{1-1}  & \multirow{2}{*}{Soot particulate NOx sensor} & Arduino Due & ESP8266 Wi-Fi SIM900 GSM & None & Almalki [10] \\ \cline{1-1}  & & PHE-45P pH sensor & & & \\ \cline{1-1}  & AW2T24 TEL-4 AI shock sensor & & & & \\ \cline{1-1}  & LDR illumination-level sensor & & & & \\ \cline{1-1}  & ALS-PT19 light sensor & & & & \\ \cline{1-1} Industry & BME680 multi-sensor & ESP-WROOM-32 & Wi-Fi & ThingBoard IoT & [PERSON] et al. [11] \\ \cline{1-1}  & Force-sensitive resistor & & & & \\ \cline{1-1}  & MPU605 6-DOF motion sensor & & & & \\ \cline{1-1}  & MQ-2 gas sensor & WeMos D1 & & & \\ \cline{1-1}  & \multirow{2}{*}{MQ-135 gas sensor & ESPduino & Wi-Fi & Mosquito MQTT & [PERSON] et al. [13] \\ \cline{1-1}  & & NodeMCU & & & \\ \cline{1-1}  & HIH6121(fixed)/ & & & & \\ \cline{1-1}  & PM15 PS and SP420 (mobile) & Raspberry Pi (RPi) & LoRa/NBiToT & Environmental DATA & Croce and \\ \cline{1-1}  & Rovira i Virgili & & & & \\ \cline{1-1}  & \multirow{2}{*}{BME680 multi-sensor} & LoRa node & TITG LoRa & The Things Network & Gonzalez \\ \cline{1-1}  & University campus & & & & \\ \cline{1-1}  & (two chemical labs) & SGP30, SGP40, SHTC3 & & & \\ \cline{1-1}  & BME280 & & & & \\ \cline{1-1}  & \multirow{2}{*}{Citizen-centric environment- monitoring IoT system} & temp/humidity/pressure & & & \\ \cline{1-1}  & LTR-559 light sensor & Raspberry Pi (+default) & Wi-Fi & Thing5 peak IoT & Mahajan [17] \\ \cline{1-1}  & MIC56814 gas sensor & & & & \\ \cline{1-1}  & SPH0645 LM4H-B sound sensor & & & & \\ \cline{1-1}  & VOC sensor & & & & \\ \cline{1-1}  & PM sensor & & & & \\ \cline{1-1}  & \multirow{2}{*}{Verkada SV11-HW} & Motion detection sensor & & & \\ \cline{1-1}  & Temp/humidity sensor & & & & \\ \cline{1-1}  & Noise sensor & & & & \\ \cline{1-1}  & BH1750 light sensor & & & & \\ \cline{1-1}  & DYU Air Box & BME680 temp/humidity/AQI & & & & \\ \cline{1-1}  & sensor sensor & TIGO ESP32 & 802.1X & Thing5 peak IoT platform & Proposed \\ \cline{1-1}  & SCD30 CO\({}_{2}\) sensor & & & & \\ \cline{1-1}  & PMS7003T dust sensor & & & & \\ \hline \hline \end{tabular}
\end{table}