Air pollution, air quality, vehicle emissions, and environmental regulations

Abstract Air quality is a perception of the quality of air we breathe and serves as a gauge for indicating the severity of air pollution on the environment and human health. Air pollution caused by anthropogenic activities have badly deteriorated the ambient air quality in the past century due to significant population growth, accelerated industrial outputs, and increased consumption of fossil fuels. Among the various pollution sources, air pollutants emanated from traffic-related activities associated with the operations of transportation modes have the most profound impact on the environment and human health. The quantity and quality of traffic-related air pollutants are alarming, as reported in 2017 that the CO2 emissions from traffic-related activities have exceeded all other major sources, and hazardous, as numerous epidemiological studies have shown evidence of adverse health effects resulting from acute or chronic exposure to traffic-related air pollutants, discussed in later chapters. This chapter provides definitions for terminologies commonly used for describing the impacts of transportation operations on the air environment and human health. Sources of air pollution are described in categories of origin (natural vs. anthropogenic), mechanism (primary vs. secondary), configuration (point, fugitive, vs. mobile), and quantity (major vs. area) of emissions. Conversion of air pollutant concentration between mass and volumetric concentration is illustrated for easy understanding of concentration units. Brief history and background of the evolution of air quality regulations and criteria pollutants are included along with trends of emissions in the United States. Characteristics and trends of transportation emissions as well as air quality regulations and enforcement are described in detail in this chapter. Lastly, impacts of transportation emission and near-road communities are briefly discussed in this chapter.