Air quality is deteriorated when harmful particulates, biological molecules and gases are present in excessive quantities in the Earth's atmosphere. Such air has a harmful effect on living organisms, food crops and the built environment. In humans, it may lead to diseases, allergies and even death. The sources of air quality degradation or pollution can be either anthropogenic or natural. Anthropogenic sources include smoke released from fossil fuel power stations and motor vehicles, waste deposition in landfills, controlled burning in agriculture, fumes from hair sprays, paints, varnish, etc. Methane released due to the digestion of food in cattle, smoke and carbon dioxide from wildfires, and radon gas generated due to the radioactive decay of radium within the Earth's crust are some of the natural sources of air pollution. All these processes result in the release of harmful pollutants into the atmosphere, which are responsible for air quality deterioration. This book brings forth some of the most innovative concepts and elucidates the unexplored aspects of air quality modeling and assessment. Different approaches, evaluations, methodologies and advanced studies on air quality degradation have been included in this book. With state-of-the-art inputs by acclaimed experts of this field, this book targets students and professionals.