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 also discovered that red rains from the Sahara region brought in alkaline substances, affecting the overall alkalinity of the rain. Overall, the reduction in sulfur emissions in Europe had a positive impact on air quality in northeastern Spain.