9. March 2006

Sunlight irradiated soil reacts with air pollutants

Photochemical reactions with organic material on the earth's surface can change the chemistry of pollutants and thereby influence summer smog. The production of nitrous acid from these reactions is a precursor to further chemical reactions in the lower atmosphere. This was shown in a joint study by researchers from the Paul Scherrer Institute, (PSI) and the universities of Wuppertal (D) and Lyon (F).

Everyone has observed how the sun warms the earth: a new lab study shows how sunlight can cause the surface of the earth to react with air pollutants. Humic acid, a product of plant decomposition was exposed to nitrogen dioxide under irradiation. The result showed that nitrogen dioxide (NO₂), a poisonous gas emitted by combustion motors, is efficiently converted to nitrous acid on these light activated surfaces.

This transformation of nitrogen dioxide has a strong influence on the chemistry of the lower atmosphere as nitrous acid is a precursor for hydroxyl radicals which are central for atmospheric chemistry. As unselective oxidation agents they breakdown air pollutants limiting their concentration in the atmosphere.

Summer smog as photochemical air pollution

Due to the chemical reactions triggered by the hydroxyl radicals, intensive sunshine can also create secondary pollution such as ozone and fine particles. These photochemical air pollutants are collectively known as summer smog and are responsible for exceeding the permissible threshold values of ozone and fine particles in Switzerland. By means of these new experiments, the researchers in Germany, France and Switzerland hope to come to a better understanding of summer smog.

The Paul Scherrer Institute (PSI) is a multi-disciplinary research centre for natural sciences and technology. The Institute’s priorities lie in areas of basic and applied research, particularly in fields which are relevant to sustainable development, as well as of major importance for teaching and training, but which are beyond the capabilities of a single university department. In national and international collaboration with universities, other research institutes and industry, PSI is active in solid state physics, materials sciences, elementary particle physics, life sciences, nuclear and non-nuclear energy research, and energy-related ecology. Unique in Switzerland, it is the largest national research institute with 1,200 permanent staff, and 1,500 scientists per year at the user-labs.