adsorbate

https://doi.org/10.1351/goldbook.A00152
A molecular species of gas, dissolved substance or liquid which adheres to or is adsorbed in an extremely thin surface layer of a solid substance.
Sources:
Orange Book, 2nd ed., p. 85 [Terms]
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2171 [Terms] [Paper]