CARBOXYLIC-ACIDS IN HIGH-ELEVATION ALPINE GLACIER SNOW

Fresh-snow samples were collected on an event basis on the Glacier de la Girose (3360 m above sea level (asl)) in the southern French Alps, during winters and early springs 1990 and 1998. In addition, a 13-m fi rn core was recovered in 1991 at the Col du Dome (4250 m asl), a cold glacier in the northern French Alps, offering the complete seasonal re cord of alpine precipitation during 3.5 years. All samples were analyz ed for total formate and acetate and for major ions using ion chromato graphy. The acidity-alkalinity was accurately measured using a titrati on technique. An almost perfect ion balance was achieved for this data set. In absence of Saharan dust transport, the high alpine snow is sl ightly acid (H+ approximately 2-20 muEq L-1). HCOO(T) and CH3COOT are generally present in alpine acid snow at very low concentrations: 0.3- 0.6 muEq L-1 in winter (January to February) and 0.6-2 muEq L-1 in ear ly spring (March to April). At Col du Dome, total acetate concentratio ns of approximately 1 muEq L-1 are observed in summer. It remains uncl ear from our results what the major sources of carboxylic acids are, a nd in particular of acetic acid, in the wintertime continental free tr oposphere, while it appears that formic and acetic acids are presumabl y mainly derived from natural sources in spring and summer. The total contribution of formic and acetic acids to free acidity is, on average , less than 15-20%. Contrary to major ions which are present in wider concentration ranges and show large variations from one snowfall to th e other, HCOO(T) and CH3COOT are surprisingly stable in acid alpine sn ow. The only significant deviation of HCOO(T) and CH3COOT from their m ean values (up to 9 and 5 muEq L-1, respectively) are observed in case of Saharan dust transport, when-precipitation pH is shifted from acid toward alkaline conditions. These observations suggest a pH partition ing effect between the aqueous and gas phases, formic and acetic acids being dissolved and neutralized as salts in alkaline cloudwater dropl ets. On a global scale, the scavenging by alkaline mineral dust could represent an important deposition process of carboxylic acids.