Nitrogen and carbon dioxide adsorption by soils.

High-resolution nitrogen (77 K) and carbon dioxide (273 K) adsorption at subatmospheric pressures has been studied for a range of model soils of various origins with different organic matter (OM) contents. It is demonstrated that N2 and CO2 molecules probe different regions of soil particles. Nitrogen is adsorbed primarily on the outer surface of soil particles, while CO2 has a higher affinity to OM domains. Low-pressure nitrogen adsorption reveals that soil particle surfaces consist of clay/mineral domains with discrete patches of OM. A linear correlation has been found between the CO2 uptake and the amount of organic carbon reduced per unit of the external surface area. A new method for discriminating the microporosity of soil particles and accessibility of OM has been proposed.