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The impact of air pollutants on the brain.

Ambient air pollution is a key modifiable disease risk factor producing detrimental health effects on millions of people across the world. In the United States, the Environmental Protection Agency has set National Ambient Air Quality Standards for 6 criteria pollutants routinely measured across the country and considered harmful to publichealth:particulatematter(PM),ozone,nitrogenandsulfur dioxides, lead, and carbon monoxide. Outdoor air pollutant exposures include complex mixtures of PM, gases, and organic (including polycyclic aromatic hydrocarbons [PAHs]) and inorganic compounds emitted directly into the air mainly from combustion of fossil fuels from gas, oil, coal, industry, and fires. Airborne PM of less than 2.5 μm and the ultrafine PM (particles <100 nm) are of special interest regarding effects on the brain because of their ability to cross epithelial, endothelial, and neural barriers, producing direct and indirect brain damage. Forty-two million people residing in cities across the United States are exposed to harmful PM of less than 2.5 μm. Ozone is the most important secondary air pollutant—a product of complex photochemical reactions of nitrogen oxides and volatile organic components. In the United States, more than 123 million people are exposed to ozone levels that are greater than the National Ambient Air Quality Standards. Air pollution components have significant variability in rural areas, from city to city, and within specific regions in the same city. Spatial air pollutant variations relate to fixed and mobile pollution sources, meteorological factors, and massive exposures from events such as the 9/11 World Trade Center attack. Because most people spend more than 90% of their time indoors, controlling the effects of indoor air pollution is also critical for brain health. Smoking, cooking, cleaning, the use of plastics and conglomerates, and, in addition, in-vehicle (cars, heavy duty trucks, buses, construction equipment, subway) concentrations of pollutants are of deep concern.