Infrared-absorbing trace gases other than CO2 are accumulating in the atmosphere. The climatic effect of these gases will be comparable and will add to that expected from CO2. Tropospheric chemistry plays an important role in the budgets and trends of two radiatively important trace gases, i. e., CH4 and tropospheric O3.The observed trend of CH4 indicates that there has been a factor of two increases in its concentration in the last 350 years and the rate of increase has become greater in the last century. The increase in CH4 is most likely due to increases in its sources, such as human activities in agriculture and energy use. Changes in the photochemical sink of CH4 may also contribute.There is strong evidence that tropospheric O3 in industrial countries has increased significantly due to anthropogenic emissions of NOx and hydrocarbons. However, the trend of tropospheric O3 has not been quantitatively established because there are large spatial and temporal variations in the distribution of O3. More extensive measurements are needed to quantify this trend.In this report we have identified the major photochemical processes that control the budgets and trends of CH4 and tropospheric O3. It is shown that human activities may have significantly perturbed the atmospheric distributions of CO, NOx, O3, nonmethane hydrocarbons, and CH4. The observed trends of O3 and CH4 are qualitatively consistent with the current understanding of their photochemistry and budgets. However, models with realistic transport and photochemical processes need to be developed to evaluate and predict the trends quantitatively.
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- Trends of Radiatively Important Trace Gases and their Relationship to Tropospheric Photochemistry
Shaw Chen Liu
- American Meteorological Society