The monitoring of natural soil CO2 emissions: Issues and perspectives

Natural soil CO2 emissions constitute a substantial portion of the carbon emitted in the atmosphere, particularly in volcano-tectonic areas where deep CO2 supply is also present because of the Earth's degassing. Hence, these emissions are considered of fundamental importance in the study of global CO2 budget estimates. Furthermore, in recent years, soil CO2 emissions have played an important role in the realm of seismic and volcanic studies as well as in the mitigation of gas-hazard-related risks. Although many methods are available for monitoring soil CO2 emissions, the comprehension and use of monitoring data can be challenging. This is because soil CO2 emissions are influenced by numerous processes and as consequence exhibit high spatio-temporal variability. In this framework, understanding the processes behind the variability of soil CO2 emissions is instrumental in improving their investigations. In addition, more suitable management of the monitoring data series is another crucial aspect of soil CO2 emission studies. In this study, we provide a detailed description of the processes that affect soil CO2 emissions and outline their impacts as functions of different features of the measurement sites. In particular, we examine the processes driven by both exogenous and endogenous factors and explain the origin of the observed variations. This study is based on the data acquired via eight monitoring stations on the island of Vulcano (Italy) from 2009 to 2017. The monitoring sites exhibited different features and covered a wide range of the soil CO2 emission values, thereby allowing a broad application of the obtained results.