Air pollution ruins the lives of millions of people in urban areas around the world. Long-term exposure even to relatively low levels of polluted air can cause or worsen a wide variety of health problems. Therefore, combating air pollution is essential. However, it turns out that doing so is not as simple and straightforward a matter as we might think.
Concentrations of atmospheric particles known as PM2.5 (airborne particles with a diameter of less than 2.5 micrometers, or a mere fraction of the diameter of human hair) are a primary indicator of the degree of pollution present in the air. By reducing those PM2.5 levels, we reduce air pollution.
The problem is, scientists argue in a new study, that reducing the level of PM2.5 in polluted air could have an unintended consequence. At higher concentrations, PM2.5 suppresses the formation of ultrafine particles because these larger particles absorb the smaller ones.
These ultrafine particles are generated, among other things, by the exhaust of diesel, which is abundant in many towns and cities. If PM2.5 concentrations are lowered, then smaller particles can proliferate, which can have serious consequences for our health.
"Ultrafine particles are generally made from combustion processes in which the growth of the particle is molecules upward and, therefore, these particles can be extremely small," explains a medical journal. Increases in contamination from these tiny particles, he adds, "have been found to be associated with a range of adverse health effects and these are very well documented."
If we lower PM2.5 concentrations and ignore the buildup of ultrafine particles, we risk making things worse, the scientists behind the new study warn. This does not mean that reducing high concentrations of PM2.5 should be less of a priority. Rather, we will have to address both types of air pollutants simultaneously, the researchers emphasize, if we really want to have clean air in our cities.
"Care is needed to avoid inadvertent worsening of the situation by reducing the mass of particles in the air, only to increase the number and toxicity of ultrafine particles as a result," said a professor of environmental sciences at Lancester University.
Author: Daniel T. Cross. Article in English