"Gas is a state of matter that has no fixed shape and no fixed volume. It was the early-seventeenth-century Flemish chemist-physician Jan Baptista van Helmont who coined the word "gas" in order to convey the idea that a gas had an indefinite shape and size. The terms gas and vapor are both used to describe the gaseous state of a substance. However, gas is primarily for a pure substance or mixture that exists in gaseous state under normal conditions. Vapor is used to describe a substance that is in gaseous state, which exists in liquid or solid state under normal conditions. A gas can be compressed above the atmospheric pressure and even nontoxic gases can be lethal when their concentrations are high enough to displace too much oxygen in the air. While too much vapor will result in the phase change from gas to liquid by condensation. Gases have lower density than other states of matter, such as solids and liquids. There is a great deal of empty space between particles, which have a lot of kinetic energy. The particles move very fast and collide into one another, causing them to diffuse, or spread out, until they are evenly distributed throughout the volume of the container. This book aims to describe some basic properties of gases, which are applicable to not only air but also gaseous air emissions. Kinetic theory of gases attempts to explain macroscopic properties of gases, such as pressure, temperature, or volume, by considering their microscopic compositions and motion. It includes a critical analysis of existing methods as well as hands-on practical recommendations. This book will be ideal for graduate students and researchers at the cutting edge of investigations into the fundamental nature of gaseous matter; this text presents the basic methods used in the treatment of gaseous flows."