L1 /   
12
CH3041
SOURCES
Sources
Most variability is seen in the trace gases.
• Biological   O2     21%  photosynthesis
                           CO2  390 ppm   respiration
eg Forest: CO2 night floor    10 ppm ­,
day canopy 25 ppm ¯     
CH4      microbes, ruminants
• Geochemical SO2, HCl                       Volcanoes
CO2, CO               Forest fires    
                          CO, (CH3)2S = DMS  Oceans
                          NOx                       Lightning
• Human   CO2  Fossil fuel consumption
CO, SO2