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 noted 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 led to lower sulfur levels in the rain, and excluding the influence of red rains, the alkalinity of the rain increased slightly.