Very Low-Cost, Internet of Things (IoT) Air Quality Monitoring Platform

Every year millions of people die prematurely due to air pollution. Many deaths occurred in cities, where fumes from vehicles, factories, and power plants filled the air with noxious particles and gases. The COVID-19 pandemic has also created a new awareness about the importance of monitoring air quality in the atmosphere and indoors. However, the available data are not widely accessible to the general public and are explicitly restricted for organizational use due to high costs. The research aims to develop a low-cost air quality monitoring device with parameters NOx, SOx, CO, O 3 , PM 2.5 , temperature, and humidity. The Air Quality Monitoring Prototype (AQMP) prototype was developed using an Internet of Things (IoT) solution based on low-cost sensors with a low-cost, low-energy, open-source Arduino system. Data is recorded every minute and stored in a database for parameters NOx, SOx, CO, O 3 , PM 2.5 , temperature, and humidity. Data communication is carried out via the cloud and displayed on smartphones and the web. The stages of work are carried out by designing systems, determining and constructing hardware, installing software, and testing. The test results show that the AQMP can operate and detect all parameters. Comparisons were made with data from the Environment Service of Bandar Lampung City, and the results showed an accuracy rate above 95%. This research has proven that low-cost air quality monitoring device can

One technology that can be developed for measuring air quality is the Internet of Things (IoT). IoT is a new concept to expand the benefits of internet connectivity. This technology provides low-cost, real-time solution capabilities that can provide large amounts of quantitative data (Aamer, Mumtaz, Anwar, & Poslad, 2018 Wall et al., 2021;Yushananta, Putri, Widyawati, & Sari, 2022). The research aims to develop a low-cost air monitoring device prototype, using the expansion of the benefits of the Internet of Things (IoT).

METHODS
The air monitoring device prototype (Air Quality Monitoring Prototype/AQMP) was developed with the expansion of the benefits of the Internet of Things (IoT). All materials (sensors and microcontroller) were obtained from general electronic and robotic materials sellers. Two types of microcontrollers were used in the research, namely ATmega2560-16AU and ESP-32. Meanwhile, the sensors used were MICS-6814, MQ136, MQ131, DHT11, DSM501A, Photorest GY-30 BH1750, Raindrop Module.
The research was carried out in four stages of activity, namely: 1) designing the IoT system, to plan the entire IoT system to be developed, including the output of the system; 2) determination and assembly of hardware, to select and determine the appropriate hardware for the system being developed; 3) embedding software, designing work programs on the system; and 4) testing, to determine the performance of AQMP.
The MICS-6814 sensor (CO, NO2 uses a voltage of 6 V and the detection range for CO ranges from 1-1000 ppm, and NO2 ranges from 0.05-10 ppm. The MQ136 sensor is used to monitor SO2 levels, with a voltage of 5 V and a detection range of 1-100 ppm. The MQ131 sensor is used to monitor O3 levels in the air with a detection capability of 0.01-2 ppm, using a voltage of 5 V. The PM2.5 sensor is used in the proposed system to measure particles in the environment. The DSM501A sensor is used to measure the concentration of small particles with a diameter of less than 2.5 microns. This sensor uses a voltage of 5 V and is able to detect PM2.5 in the range 0-1.4 mg/M 3 .
The DHT11 sensor is used to detect humidity and air temperature. This sensor uses a voltage of 3.3-6 V, with the ability to detect humidity 0-100%, and temperature -40-80 0 C. This study also used the Photorest GY-30 BH1750 sensor to detect dark or light weather conditions, as well as the Raindrop Module sensor to obtain rain or dry information. Both sensors use a voltage of 5 V.

RESULTS AND DISCUSSION
Research has succeeded in developing a low-cost prototype of an air monitoring device (Air Quality Monitoring Prototype/AQMP), using the expansion of the benefits of the Internet of Things (IoT). To achieve costeffectiveness, low-cost sensors and a low-cost Arduino system are used, with minimal energy, and are open. Data is recorded every minute and stored in a database for parameters NO2, SO2, CO, O3, PM25, temperature, and humidity. Data communication is carried out via the cloud and is displayed (interface) on a smartphone or PC.

IoT system design
The AQMP is designed (Figure 1) to simultaneously measure air quality and weather, using some detection components (sensors) managed by a microcontroller chip. Furthermore, data is sent by the Wi-Fi and cellular modules, and data communication is in the cloud system so that it can be received and allows for remote control and online data access. The sensor periodically (units of minutes) monitors the air quality and sends it; the data can be monitored and accessed without limits using a smartphone or PC with internet.
The device is also designed with a datalogger in mind, making it possible to save every data. The systems used are Arduino Mega and ESP-32, with low-cost considerations, the ability to process data from multiple sensors, and are open.  (Table  1), grouped into sensor modules, microcontrollers, accessories, and connectors. The entire sensor is connected via cable with the microcontroller at 5 volts supplied by the adapter.
The device detects air quality parameters (NO2, SO2, CO, O3, PM2.5, temperature, and humidity) in the environment. This device uses seven sensors, namely sensors MICS-6814, MQ135, MQ136, MQ131, DHT11, DSM501A, Photorest GY-30 BH1750, Raindrop Module. The sensor is connected to a microcontroller (Arduino ATmega 2560-16AU) at an output voltage of 5V. The processed data is sent via the GSM SIM900A module to the Thinger.ESP-32 cloud system, displayed via a smartphone or PC via the internet network. Data storage using the Mini Data Logger module in minutes.

Software
The software design is implemented in two parts: acquiring front-end display data with the appropriate software and selecting software considering the low cost, minimal energy, and open (open-source). The program used in AQMP is Arduino for data acquisition using C/C++ language and Thinger-ESP32 for front-end display analysis.
The data acquisition software checks the sensor every five seconds, then saves the sensor data to an SD card and a MySQL database on the Thinger.io server. In addition, all data collected from sensors is entered into the MySQL database through prepared statements. This approach adds security to web applications by separating queries from data so that the data submitted cannot be used to change how queries are executed, thereby preventing injection attacks.

Trial
The test was carried out to determine the AQMP's ability to detect air quality parameters, compared to the results of standard measurement device, namely the AQMS (Air Quality Monitoring System) owned by the Environment Service of Bandar Lampung City. The test was carried out on 10 measurements.  Table 2 shows that the average total PM2.5 parameter measurement results with AQMS and AQMP were 3.4 µg/M 3 and 3.3 µg/M 3 , so the AQMP error rate was only 2.941%. In the SO2 test, the measurement results obtained were 42 .8 µg/M 3 and 43.9 µg/M 3 , so the AQMP error rate is 0.234%. CO measurement results, the average measurement results are 2091 µg/M 3 and 2090 µg/M 3 , so the AQMP error is 0.057%.
In the O3 measurement, the average AQMS and AQMP were 43.9 µg/M 3 and 43.8 µg/M 3 , AQMP error rate of 0.228%. At the same time, the NO2 measurement results were 33.7 µg/M 3 and 33.6 µg/M 3 , an AQMP error of 0.297%. The results of this test show that the error rate is still far below 5%. The percentage of sensor measurement error of less than 5% indicates the device is feasible to use (Junaidi & Prabowo, 2018).

CONCLUSIONS AND SUGGESTIONS
This research has proven that low-cost air quality monitoring device can be developed with IoT and provide accurate results. This research simultaneously supports the concept of "Going Green" to maintain a healthy and clean environment for present and future generations.