A Preliminary Evaluation of WMO-UNEP Precipitation Chemistry Data: MARC Report Number 22

This document presents an evaluation of precipitation chemistry data collected from the WMO-UNEP network between 1972 and 1976, focusing on Europe and North America. The document analyzes the distribution of sulphates and nitrates to provide a general picture of atmospheric composition. It compares sulphate concentrations from the 1970s with earlier data from the 1950s, revealing a significant increase of 50-100 per cent in precipitation over Europe. The rate of increase in North America was found to be slower, which may be partly due to emission control measures introduced during the seventies. The report also makes an initial attempt to analyze nitrate distribution, noting that values in the United States are more evenly distributed but often higher than in Europe. The findings highlight the importance of ongoing monitoring and the need for improved data quality and intercalibration of analysis methods.