Through comparison of snow-pit NO3 – profiles from central East Antarctica and the northern Qinghai-Tibetan Plateau (QTP), we conclude that NO3 – peaks in the uppermost surface snow layers in central East Antarctica are not related to an atmospheric signal and that they need to be accounted for by post-depositional effects. Such effects, however, are not found in the snow-pit NO3 – profiles from the northern QTP. NO3 – can be deposited as a gas (HNO3 –) or as a neutral salt, particularly by

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... tion with ammonia to form NH4NO3, or fixed by sea salt or terrestrial dust (Mulvaney and others, 1998). Thus, a difference in speciation between NO3 – in snow layers in East Antarctica and at the northern QTP is suggested as the reason for the different post-depositional processes of NO3 – in the two areas.