A review of the observations and origins of the spring ozone maximum

Measurements of ozone throughout the troposphere clearly show an annual cycle. Over the last couple of decades it has become apparent that the measured annual cycle of ozone in certain locations shows a distinct maximum during spring and the magnitude of the maximum seems to have increased. There has been much debate as to the origins of this phenomenon. There is broad agreement that much of the ozone found in the troposphere is of photochemical origin. In contrast, there is still no over-arching consensus as to the mechanisms that lead to the formation of the spring ozone maximum. Part of the problem would seem to lie in the interpretation of measurements and the interactions of processes occurring on differing scales from the local to the global scale. This paper reviews both the experimental evidence concerning the origin of the spring ozone maximum and the supporting modelling studies. The roles of stratospheric–tropospheric exchange and photochemistry in the appearance of the spring ozone maximum are discussed; the evidence for various mechanisms for accumulation of ozone and its precursors are considered. The paper concludes with a summary of the state of the knowledge with respect to the spring ozone maximum and some possible areas for future consideration. The spring ozone phenomenon may well be a proxy for the continuing changes to the atmospheric composition owing to manʹs activities. Understanding the appearance of the spring ozone maximum and the mechanisms that lead to its formation therefore remains an issue fundamental to tropospheric chemistry.