Agriculture contributes to the atmosphere's sulphur content

Agriculture contributes to

the atmosphere's sulphur content

Associate Professor Anders Feilberg climbing the towers of the air scrubber that uses copper ions to remove hydrogen sulfide from the air. Photo: Melissa B. Kirkeby Yildirim.

For the first time, researchers can determine the atmospheric content of sulphur caused by animal manure. A new study demonstrates that hydrogen sulphide from animal manure accounts for about one third of the total Danish sulphur emissions to the atmosphere.

Present emission inventories and climate models do not consider agricultural production as being a significant contributor of atmospheric sulphur. A recent study from Aarhus University proves that this assumption is wrong. Agricultural emissions of sulphur cannot be neglected and may be very important in areas with intensive livestock production.

The study was recently published in the scientific publication Nature Communications.

Livestock manure emits sulphur mainly in the form of hydrogen sulphide, which is quickly converted into sulphur dioxide in the atmosphere and thus has the same impact. The study further shows that in areas with a high livestock density, sulphur from animal manure accounts for about half of the known sulphur emissions (in the form of sulphur dioxide) to the atmosphere. This means that hydrogen sulphide from animal manure accounts for approximately one third of total Danish sulphur emissions to the atmosphere.

It may seem strange that the significant contribution of atmospheric sulphur from agriculture has been overlooked. However, only few and very limited studies exist within this area, in Denmark as well as in other countries.

This is partly due to the difficulties of measuring sulphur emissions from livestock production, explains Associate Professor Anders Feilberg. He is one of the researchers behind the study.

“The development of PTR-MS (proton- transfer-reaction mass spectrometry) allows us to monitor the emissions of sulphur compounds from livestock production very accurately and with a high time resolution, which provides extensive and very detailed data material,” says Associate Professor Feilberg.

In principle, PTR-MS acts as an online molecular balance, measuring the weight and number of atmospheric molecules.

New opportunities to limit emissions
In the atmosphere sulphur and other substances form chemical compounds and produce harmful particles.

Based on this, recent years have witnessed significant efforts to reduce the atmospheric sulphur content. For obvious reasons, focus has been on well-known sulphur emission sources – primarily oil, coal and natural gases, which emit sulphur to the atmosphere via combustion engines, power stations, etc.

This study provides new opportunities to increase the focus on reducing sulphur emissions from livestock production.

The studies demonstrate that hydrogen sulphide emissions are caused mainly by slurry evaporation from pig and cattle houses. In addition, there is a minor loss in relation to storage and slurry distribution.

Aarhus University currently carries out research that is targeted towards the development of air purification technologies for animal housing, and technologies to reduce the evaporation from animal manure. These technologies will contribute to reducing sulphur emissions.

However, Anders Feilberg points out that emission of hydrogen sulphide from livestock production has a close relation to the emission of ammonia. Action plans for improved utilisation of nutrients in animal manure will therefore contribute to reducing emissions of hydrogen sulphide.

Affecting climate models
This new knowledge is important to the development of climate models. As mentioned previously, sulphur becomes part of chemical compounds and forms airborne particles. These particles reflect the rays of the sun, which in turn helps reduce global warming caused by climate gases. At the same time, the particles contribute to cloud formation, which increases reflection.

“The agricultural contribution has not been included in the climate models so far, and in the global perspective, this new knowledge will contribute to improving climate models,” he says.

Yet, there is a need for more measurements in more countries before the significance in a global perspective can be clarified.