Global changes to atmospheric chemistry

Changes in atmospheric concentrations of trace gases provided early evidence of widespread changes within the biosphere. Trace gas production by plants and in soils increased in response to human pressures. Long lived trace gases like nitrous oxide and methane are greenhouse gases and play an important role in stratospheric chemistry. Photochemically active compounds, isoprene, nitric oxide, and carbon monoxide, are determinants of tropospheric ozone concentrations and thus regulate the oxidizing capacity of the troposphere. Inclusion of isoprene produced by plants in 3-D chemical transport models increases atmospheric concentrations of ozone and carbon monoxide substantially. In return, terrestrial ecosystems are sensitive to atmospheric composition, responding to increased N deposition with increased C uptake, and soil acidification, and responding to increased ozone concentrations and UV-B with decreased plant production.