Neutrons detect air pollution

Tradition versus air pollution: In the region around Ponte de Sor (Portalegre County, Portugal), coal has been produced for centuries by smoldering wood in charcoal kilns. But traditional charcoal production not only provides jobs, but also bad air.

Complaints about the smell, clouds of smoke in winter, reports of asthma and other respiratory diseases are not uncommon, says chemist Dr. Nuno Canha of the Instituto Superior Técnico at the University of Lisbon. However, there have been no official measurements of air quality.

Lichens absorb pollutants from the air

In search of a method to measure air quality in a roundabout way, Dr. Nuno Canha came across the prompt gamma activation analysis (PGAA), which is possible thanks to the neutrons of the FRM II in Garching. Here, neutrons activate traces of pollutants, which are then still detectable even in the smallest concentrations.

For his study, Dr. Canha collected lichens growing on olive tree trunks in the area of the charcoal kilns. Lichens are a community of fungi and algae without roots. "Because they absorb all their nutrients through the air, they are excellent indicators of air quality," says Nuno Canha. He picked one batch in spring and the other in fall to rule out seasonal differences.

More stress near the coal piles

One indicator of lichen exposure to air pollutants is their conductivity, because the fine cell membranes break under extreme stress, which increases the lichens' conductivity.

Nuno Canha found that lichens in the immediate vicinity of coal-producing furnaces had twice as high conductivity in the fall as lichens further away from the furnaces. In spring, this difference between individual sites was not as noticeable.

The scientist suspects that this is due to the preceding rainy period before picking the lichens in spring, which lower the stress level of the creatures, while it was rather dry before picking in autumn.

Other sources of pollution in autumn and spring

Together with TUM scientists Dr. Zsolt Révay and Dr. Christian Stieghorst, Nuno Canha detected 22 elements in the lichens using prompt gamma activation analysis.

The concentrations of the elements phosphorus (P) and sulfur (S), which are present in smoke from burning wood, differed particularly strikingly in the fall. The lichens collected by Canha in the immediate vicinity of charcoal burners contained more than twice as much P and the highest concentrations of S in the fall, compared to all other locations.

"That fits well with the conductivity measurements, which also attest to higher stress in the lichens in the fall right next to the furnaces," Canha says. In contrast, in the spring, it was the lichens near a populated area with little traffic that contained more sulfur and phosphorus. Nuno Canha attributes this to exhaust fumes from private wood stoves and meteorological influences.

Nuno Canha hopes that the study will bring the impact of traditional coal production on air quality more into the focus of the authorities. For example, air filters could remove pollutants from the exhaust gas.

Publication:

Nuno Canha, Ana Rita Justino, Catarina Galinha, Joana Lage, Christian Stieghorst, Zsolt Revay, Célia Alves, Susana Marta Almeida-
Elemental characterisation of native lichens collected in an area affected by traditional charcoal production
Journal of Radioanalytical and Nuclear Chemistry 325:293-302 (2020).
https://link.springer.com/article/10.1007/s10967-020-07224-3

More information:

The work was funded by the Portuguese Fundação para a Ciência e a Tecnologia.
Research Neutron Source Heinz Maier-Leibnitz: https://www.frm2.tum.de

Heinz Maier-Leibnitz Center: https://mlz-garching.de/pgaa/de

Técnico Lisboa: https://tecnico.ulisboa.pt/en/