Carbon-supported metallic iron nanoparticles with an average diameter of 2.3 nm were studied by in situ Mossbauer spectroscopy at temperatures down to 5 K and with applied magnetic field up to 4 T. Nitrogen chemisorption at 300, 600 and 700 K on the iron particles was found only to affect the iron atoms in the surface layers, resulting in surface iron atoms bonded to nitrogen in a number of different types of environments.