# Development of Multi-Item Air Quality Monitoring System Based on Real-Time Data
## 1 Introduction  
The risks posed by air pollution lead to side effects such as poor public health and increased mortality [1]. According to the World Health Organization (WHO), 4.2 million people die each year from outdoor air pollution and 3.8 million people die from indoor air pollution [2]. The premature mortality rate from air pollution is expected to double by 2050, which is recognized as the world's most serious environmental and health threat [3]. Particles smaller than 2.5 \(\upmu\)m are called ultra-particulate matter, which float in the air and can be easily inhaled by humans. They affect premature death and may travel intercontinentally, affecting air quality and public health [4]. [PERSON] et al. (2021) reported that air pollution affects chronic disease and may be associated with increased mortality associated with COVID-19, and that exposure to air pollution reduces immune responses, promoting virus penetration and replication [5]. The size of the dust particles varies from a few nanometers to several tens of micrometers; however, generally, in the literature, the first particles are less than 2.5 \(\upmu\)m, the second particles are between 2.5 \(\upmu\)m to 10 \(\upmu\)m, and the third particles are up to 100 \(\upmu\)m [6]. [PERSON] et al. (2012) reported the toxicity of particulate matter (PM), as they penetrate the alveoli and bronchi and are deposited mainly in the bronchi and are filtered by the pharynx [7]. [PERSON] et al. (2018) reported that the exposure to particulate matter less than 2.5 \(\upmu\)m in diameter decreased the world average life span in 2016 by more than 1 year [8]. Particles less than 1.0 \(\upmu\)m in diameter negatively affect the air-blood barrier near the lungs and cause illnesses such as stroke, lung cancer, chronic obstructive pulmonary disease, and respiratory infections [9]. [PERSON] et al. (2020) concluded that particulate matter can have a devastating effect on vulnerable groups, including the elderly, pregnant women, and children, and it appears that it is closely related to mortality [9]. Combustion gases such as gaseous carbon monoxide, carbon dioxide, NOx, SO2, and volatile organic compounds negatively affect the air quality and the human living environment [10]. Carbon monoxide is a product of the incomplete combustion of fossil fuels and causes poisoning [11]. Carbon dioxide exists in a relatively high concentration in the air and is used for the human body such as in carbonated drinks and fire extinguishers, but it is also a product of fossil fuel combustion and is a substance that absorbs infrared rays and causes a greenhouse effect [12]. Nitrogen oxides are generated by the combustion of fossil fuels in engines and industrial processes, and NO2 is toxic and may cause lung-related health deterioration [13]. Sulfur dioxide mainly occurs in industrial activities and not only irritates the airways but also affects acid rain [1]. As hazardous chemicals such as volatile organic compounds, propanol, and toluene, they exhibit high vapor pressure at room temperature and can be dispersed in certain concentrations in the air, causing air pollution [14]. Methane is colorless, odorless, and non-toxic, but at high concentrations, it causes the risk of asphyxiation and explosion due to oxygen depletion [9]. For this reason, real-time measurement and monitoring is very important to identify air quality problems. [PERSON] et al. (2021) developed an IOT-based air monitoring device that can measure O3, SO2, and CO [15]. [PERSON] et al. (2014) developed a measuring instrument that can measure CO2, VOCs, SO2, NOx, CO, PM, and ozone to check indoor air quality in real time and developed factors that change indoor air quality (wind, location, airflow, density, and size) were investigated [16]. [PERSON] and [PERSON] (2021) developed an IOT smart air control system that is transmitted in real time through Wi-Fi using PM, CO, and CO2 sensors [17]. Recently, many commercial air quality measuring devices have been released for real time air quality measurement [18; 19].