A firn core was recovered in 1980 from an altitude of 5340 m on Mount Logan (60°36'N, 140°30'W) and dated (±0.5 a) for the last 30 a by oxygen isotope and artificial radioactivity measurements. We present in this note the results of the chemical analysis of a continuous sequence of this core. 11 m long, cut in 110 individual samples. The time period studied is from 1953 to 1966.

In order to overcome problems of contamination considerable precautions were taken in sample handling and laboratory work. Only the central part of the firn core was melted for chemical analysis. , , Cl⁻, Na⁺ and were determined by ion chromatography and strong acidity by a titrimetric method.

Sea-salt contribution (as indicated by Na⁺ concentrations, average value 1.4 ppb) was found to be extremely low. All samples were acidic in the range 1–6 μeq 1⁻¹H⁺. The mineral acids H₂SO₄ and HNO₃ are the major trace compounds in Mount Logan snow, and occur with about the same concentration (0.9 μeq 1⁻¹ as an average). Neutralization by NH₃ is generally unimportant (∼11% of the total acidity).

Depth profiles of , and H⁺ exhibit seasonal patterns with maxima occurring generally in summer. Explosive volcanic eruptions of global concern (such as Mount Agung in 1963 and Bezymianny in 1956) are not recorded. The background acidity of snow at this altitude is assumed to be mainly derived from gaseous S and N tropospheric compounds, possibly of biogenic origin. In particular our data indicate no clear trend related to the increasing atmospheric acid pollution of the northern hemisphere.