![]() As a consequence, atmospheric emission inventories indicate that the proportion of NEE has increased, (10) widely exceeding exhaust emissions. This has been effective in progressively driving down gaseous pollutants and PM from the exhaust of new vehicles. ![]() In developed countries, tightening emission regulations for gasoline and diesel vehicles has mandated technological upgrades of combustion control and exhaust emission treatment systems. ![]() (13) While invariably being associated with coarse-mode PM, a considerable fraction of abrasion-derived particles exist within the fine and ultrafine fractions, (14,15) engendering NEE with a high capacity for harm owing to a larger reactive surface area and the ability to penetrate deeper into the lung and possibly into the blood to impact other organs in the body. (12) These metals, as well as those such as Fe from brake wear, catalyze the formation of reactive oxygen species (ROS) in the respiratory tract lining fluids, challenging antioxidants and metal-binding proteins that protect the epithelial surface of the lung. (11) The UK emissions inventory estimates mass contributions of 47% and 21% to national total airborne emissions of Cu and Zn, respectively. NEE, especially those from brake and tire wear, are an important source of metals in urban atmospheres. ![]() In contrast, particulates from NEE have been woefully understudied. ![]() (9,10) Most epidemiological and experimental research into traffic-related pollution focuses on particulate and gaseous pollutants emitted from the exhaust, particularly from diesel-fueled vehicles. These comprise of particles from mechanical abrasion of brakes and tires, erosion of road surfaces and resuspension of a mixture of dust that accumulates on road surfaces, and volatile organic compounds from evaporative loss of fuels and release of solvents. Road transport is also a source of nonexhaust emissions (NEE). Traffic-derived air pollution comprises a mixture of gaseous pollutants and PM from fuel combustion and lubricant volatilization in exhaust (tailpipe) emissions. ![]()
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