It's easy to see air pollution when it settles as smog over a city. Yet even in rural areas, where the air looks clearer, researchers have found unhealthy particles floating in the atmosphere.
Fine particulate matter less than 2.5 micrometers in diameter is thought to cause the most harm to human health, as these pollutants are small enough to seephas therefore set a safety threshold for ambient PM2.5 levels, and yet this line in the sand overlooks the nuances of intrinsically toxic chemicals.
When researchers in the United States compared three urban areas to one rural area in the midwest, they found similar levels of oxidative potential at all four sites. That was true even though the rural site had a relatively lower mass of PM2.5. Analyzing the composition, mass, and oxidative potential of these samples, the team found a poor correlation between the mass and toxicity of fine particulate matter.Floating traces of iron and organic carbon, for instance, were strongly correlated with cellular oxidative potential throughout the year. Other industrial chemicals, like lead, aluminum, copper, and manganese, tended to increase during winter and fall.