Potential Sources, Formation Routes, and Health Effects of Nitrogen Dioxide (NO2) on Indoor Air Quality, Human Health, Safety, and the Environment: A Review

Abstract

Since human beings spend 80-90% of the day inside houses, educational and recreation centers, office blocks, or automobiles, the quality of air within these buildings or structures is crucial for human health and safety. Hence, indoor air quality (IAQ) highlights the general characteristics of indoor air that affect the state of health, thermal comfort, and well-being of humans. Despite numerous regulatory standards, framework policies, and monitoring plans proposed for IAQ, the occurrence of indoor pollutants including radon (Rn), ozone (O3), and oxides of carbon, sulfur, and nitrogen have become common. Many studies contend that nitrogen dioxide (NO2) is a major indoor air pollutant and one of the most poisonous on Earth. It is a reddish-brown gas generated from the oxidation of nitrogen oxides (NOx) and molecular oxygen or O3 or the high-temperature combustion of solid fuels. This paper presents an overview of the potential sources, formation routes, and health effects of NO2. According to reviewed literature, the occurrence, concentrations, and ratios of NO2 in the indoor environment are affected by residential factors, weather/climate, and proximity to NO2 sources indoors, such as burners, ovens, and stoves. Furthermore, long-term exposure to NO2 causes diabetes, heart, cardiovascular, hypertension diseases, severe cough, hemoptysis, pediatric lung edema and, more recently, fatalities arising from COVID-19. Therefore, the overdependence on polluting fuels that generate NO2 must be minimized or eliminated to improve IAQ and protect human health, safety, and the environment. Future design plans for constructing kitchens, homes, offices, automobiles, factories, and power plants must incorporate smart sensors or ventilation systems for detecting, monitoring, or removal of exhaust gases, including NO2.