Fog frequency and chemical composition of fog water—a relevant contribution to atmospheric deposition in the eastern Erzgebirge, Germany

After successful air quality control in Central Europe has taken effect and previous problems related to atmospheric deposition supposedly solved, a new study on fog-related inputs to mountainous areas yields some surprises. The hydrological relevance of fog reaches significant levels at altitudes above 800 m a.s.l. In this study, some 25% of the water input derived from fog, equivalent to 152 fog hours per month (10% of which were sampled; 8 sites, one sampler each). The fog droplets dissolve more aerosol particles and generally contain significantly higher ion concentrations than rainwater. The related enrichment factors lie between 2.5 and 38, with 6–7 for the most relevant species. For some of the potentially noxious substances, concentrations excel the thresholds that protect, e.g., forest health. Even though fog chemistry has seen major changes as of the 1980s, and ion concentrations did decrease, the input still is relevant and contributes to a continuing strain. Interestingly, forests themselves alter the ionic composition of fog water, and a distinct trend becomes visible from open field deposition to forest interior sites.