# Low-Cost IoT Air Quality Monitoring Station Using Cloud Platform and Blockchain Technology
## 2 Literature Review  
As a result of the air pollution problem and its dangerous impact on people and human beings, there is much research on air quality and how to detect it with many different methods. One institute conducted an experiment near New Delhi, India, in an industrial zone with a diameter of one kilometer. It found that the parts per million (PPM) was more than 10,000, which is very high and unacceptable because a pollution level exceeding 600 PPM is unsafe for humans [4]. We found many research papers discussing this topic. A study introduced an architecture designed for low-power wide-area IoT devices. The system uses sensors to detect the presence of harmful gases, transmitting these data seamlessly to a web-based server through a radio frequency (RF) module and common computer. Then, the data stored in the web-based server are analyzed [5]. Another study developed a solution for air monitoring. They used temperature and humidity as parameters to assess the quality of air and build a wireless sensing and monitoring platform consisting of sensors and a microcontroller. The data are stored on a personal computer (PC) and can be accessed remotely via an Android phone [6]. In another study, the authors developed a solution for air quality monitoring using carbon monoxide, carbon dioxide, and smoke as the parameters to evaluate the air quality, measured using the MQ7, MQ135, and MQ6 sensors, respectively. To detect the measurements and process these signals from the sensors, a microcontroller was used, and a liquid crystal display (LCD) screen was used to monitor the data. They added an ESP8266 Wi-Fi module to the system to access it remotely [7]. Other researchers in the same field of air quality monitoring used an Arduino Uno with the MQ7, MQ135, and DHT11 sensors to detect different gases--carbon monoxide, carbon dioxide, and temperature, respectively. Also, they used a GP2Y1010 AU0F dust sensor to detect dust and an ESP8266 to connect to the Arduino via a Wi-Fi network to transmit the data to any related server [8]. In [9], the authors used the concept of merging IoT and blockchain technologies to collect air quality measurements by using three sensors, MQ2, MQ7, and MQ135, to collect the parameters of smoke, carbon monoxide, and carbon dioxide, respectively. They measured the gases to indicate the air quality and used the concept of blockchain technology to connect to an Arduino Uno. Different sensors were used to measure the parameters of monoxide, dioxide, temperature, and humidity, respectively. All of these sensors were connected to an Arduino and then connected to a Raspberry Pi, which sends the data to an online platform and then connects to a cloud service. This results in very high power consumption and a relatively higher cost of this solution [10]. In the paper by [11], the research is also related to climate monitoring. The paper presents a solution consisting of a Raspberry Pi, which is a mini computer on a single chip. It is connected to a DHT11 temperature and humidity sensor and a laptop, which uses software to simulate a blockchain platform. The above paper presented a solution that uses carbon monoxide, carbon dioxide, and temperature as the parameters to evaluate the air quality by an IoT-based system for a smart healthcare solution. It can track a patient's current room conditions in real time by connecting MQ9, MQ135, and DHT11 sensors to an ESP32 processor and then sending the data to a web server to assess the health environment for healthcare purposes. The system in [12] measures variables like humidity, altitude, atmospheric pressure, and the concentrations of dangerous chemicals, like NO\({}_{2}\) and CO\({}_{2}\), in the atmosphere. In another study, the MQ-135, DHT-11, and BMP280 sensors were used to collect data, which were processed by the ESP32 board. A fuzzy inference system (FIS) model used a reasoning technique to perform parameter classification and the message queuing telemetry transport (MQTT) protocol to send the gathered data over the Internet to a website [13].