The study looked at changes in air pollution in the Montseny mountains in Spain from 1983 to 1994. They found that sulfur concentrations decreased significantly, while other pollutants stayed about the same. The pH of rainwater became less acidic over time. The researchers think that regulations reducing sulfur emissions in Europe helped lower pollution levels in the area. They also noticed that occasional red rains from the Sahara brought in extra alkalinity and base cations. Overall, the study suggests that efforts to reduce sulfur emissions have had a positive impact on air quality in the region.