Variations of tropospheric HCl amounts over northern Sweden

Abstract

Unexpectedly large variations of tropospheric HCl zenith column amounts were observed over Kiruna, Northern Sweden, in the arctic winters of 1991/92 and 1992/93. Trajectory calculations prove a strong dependence of tropospheric HCl variation on the origin of the air mass observed. This effect cannot be explained by different altitudes of the tropopause caused by dynamical processes. Polar maritime air contains 0.67 ± 0.11 × 1015 more HCl molecules cm−2, in terms of tropospheric zenith column amounts, than maritime midlatitudinal air. The latter contains 0.39 ± 0.16 × 1015 more HCl molecules cm−2 than continental air from midlatitudes. The HCl loading of arctic air is comparable to that of maritime polar air, except for one measurement on January 28, 1993, which showed significantly less tropospheric HCl. Tropospheric chlorine activation, along with ozone destruction in the troposphere, is considered a candidate for explanation. Furthermore, HCl strongly correlates with CH2O.