We analyzed 13 years of hourly measurements of SO 2 , NO x , and O 3 , at forest ecosystem research sites in SE Germany. A quasi-continuous data record was obtained by combining data sets from two locations. Before interpreting trends in the combined data set, we analyzed if the change of location introduced a systematic bias. We employed autocorrelation functions, Hurst statistics, complexity analysis, and recurrence quantification and found that the partial data sets exhibited no indication of the presence of any bias. For SO 2 , we also compared the data from the forest sites with data obtained in nearby cities and also found no indications for any systematic effects. Applying nonparametric trend statistics we found a significant decrease of the SO 2 . Most of the observed decrease is due to the reductions of SO2 emissions in eastern Germany, but reductions in western Germany and the Czech Republic also played important roles. For O3 , we observed a significant increase, the causes of which are unclear from our data alone. No trend was identified for NOx . |
