The increasing world population and the need to grow enough food for all people are the main reasons for changes in how the land is used. Often forests are cleared to create new cultivation areas. Besides their loss as an absorbing medium for the greenhouse gas carbon dioxide, the change in vegetation and especially the soil type may alter the exchange of volatile, reactive organic compounds. Particularly monoterpenes got into focus in recent soil-atmosphere exchange studies. These compounds can be oxidized in the atmosphere and thereafter form particles, which impact local air quality, weather and climate.
To examine the effect of two differently used soils on monoterpene exchange rates, we developed and set-up two novel soil chambers in a forest and a cornfield less than 50m apart from each other. During summer 2020, samples of the incoming and outgoing air of the chamber were collected once a day. The chamber was kept open when no samples were taken to keep the conditions of the analysed soil as natural as possible. The samples were analyzed later in the laboratory by gas chromatography with a flame ionization detector, and the exchange rates for six different monoterpenes in both measurement sites were calculated. Surprisingly, the identified exchange rates for all analyzed monoterpene species were negative. That means the soil surface has absorbed monoterpenes. The higher the ambient mixing ratios of the different monoterpenes, the higher was the observed soil uptake. The exchange rates for the forest site were generally decreasing with increasing ambient temperature, while the data for the cornfield soil mostly showed the opposite relation.