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Global overview

Over the past three decades, anthropogenic emissions of chemical compounds into the atmosphere have caused many environmental and health problems. Some chemicals, such as chlorofluorocarbons (CFCs), are produced deliberately and end up in the atmosphere by accident from equipment or goods. Others, such as sulphur dioxide (SO2) and carbon monoxide (CO), are unavoidable by-products of burning fossil fuels. Urban air pollution, acid rain, contamination by toxic chemicals (some of them persistent and transported over long distances), depletion of the stratospheric ozone layer and changes in the global climatic system are all important environmental threats to ecosystems and human wellbeing.