Changing chemical composition of the atmosphere Variations and trends

2 Changing the chemical composition of the atmosphere Variations and trends 

The chemical composition of the atmosphere is determined by the emission of compounds from marine and terrestrial biospheres, anthropogenic sources and their chemistry and deposition processes. Biogenic emissions depend on physiologi- 

Sweden, background (1954/55) Central Europe, background (1950s) 200-300 12 (2-19) 2-3  

With the aim of establishing a chemical chmatology (see also Chapter 3.4) it is important to analyse and understand the reasons for concentration variations on different times scales to the determine trends of climate change, and separate natural- from man-made-caused influences to establish natural reference values of concentrations. 

NO these historical aspects are almost forgotten. Table 2.73 shows values from around 1950 that also support the data shown in Fig. 2.59. It should be recognized that measurement methods (air sampling and analytical procedure) changed over time, and it is often impossible to characterize the accuracy of early published data. 

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