<![CDATA[Air quality has a significant impact on human health; however, access to real-time air quality information remains limited. This study aims to design an affordable and accessible IoT-based air quality monitoring system. The system was developed using a NodeMCU ESP8266 microcontroller as the central data processing unit, an MQ-135 sensor to detect hazardous gas concentrations, such as ammonia and CO₂, and a DHT11 sensor to measure air temperature and humidity. Sensor data are displayed directly on a 0.96-inch OLED screen and wirelessly transmitted to an IoT platform through the ThingSpeak web server, allowing the data to be monitored through a website using a smartphone browser. The method used in this study was the prototyping method, which included hardware and software design, system implementation, and testing. The test results showed that the DHT11 sensor had an average temperature measurement difference of approximately ±1.8°C and a humidity measurement difference of ±4.5% compared with a digital reference measuring instrument. The MQ-135 sensor demonstrated a response to changes in gas concentrations, with an average response time of 3–5 seconds under varying air exposure conditions. The system was able to classify air quality into three categories—“Fresh Air,” “Poor Air,” and “Danger”—in real time, with a 95% success rate for data reading and transmission to the server during connectivity testing. These results indicate that the proposed system can operate reliably and can be utilized as an IoT-based air quality monitoring and early warning system.]]>
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