Taking the air :Understanding our background atmosphere

The article explains how a global network of monitoring stations is giving people more of the information they need. In remote locations, variations in atmospheric composition can be caused by large-scale changes in man-made emissions, in weather circulation patterns, or from variations in natural processes. A central challenge from background measurements is to work out which changes in atmospheric composition are a result of human activity and which are natural, something which can be achieved with the help of numerical models. The most accurate, however, are long-term measurements of atmospheric composition made on the ground from atmospheric observatories. These surface measurements are considered the gold standard against which other observations are compared. This is partly because they cover a long period of time, but also because they are made under optimum measurement conditions where the instruments are most likely to perform at their best.