Stratospheric ozone attenuates harmful ultraviolet radiation and protects the Earth’s biosphere1. Ozone is also of fundamental importance for the chemistry of the lowermost part of the atmosphere, the troposphere1,2,3,4,5,6,7,8. At ground level, ozone is an important by-product of anthropogenic pollution7, damaging forests and crops5,6, and negatively affecting human health9. Ozone is critical to the chemical and thermal balance of the troposphere10 because, via the formation of hydroxyl radicals, it controls the capacity of tropospheric air to oxidize and remove other pollutants1. Moreover, ozone is an important greenhouse gas, particularly in the upper troposphere1. Although photochemistry in the lower troposphere is the major source of tropospheric ozone2,7,11, the stratosphere–troposphere transport of ozone12,13,14,15,16,17,18,19 is important to the overall climatology, budget and long-term trends of tropospheric ozone3,4,8,12. Stratospheric intrusion events, however, are still poorly understood. Here we introduce the use of modern windprofiler radars20,21,22 to assist in such transport investigations. By hourly monitoring the radar-derived tropopause height23,24,25 in combination with a series of frequent ozonesonde balloon launches, we find numerous intrusions of ozone from the stratosphere into the troposphere in southeastern Canada. On some occasions, ozone is dispersed at altitudes of two to four kilometres, but on other occasions it reaches the ground, where it can dominate the ozone density variability. We observe rapid changes in radar tropopause height immediately preceding these intrusion events. Such changes therefore serve as a valuable diagnostic for the occurrence of ozone intrusion events. Our studies emphasize the impact that stratospheric ozone can have on tropospheric ozone, and show that windprofiler data can be used to infer the possibility of ozone intrusions, as well as better represent tropopause motions in association with stratosphere–troposphere transport.
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This work was funded primarily by the Canadian Foundation for Climate and Atmospheric Science, and by the Natural Sciences and Engineering Research Council of Canada. We are grateful for logistical and financial support provided by Environment Canada. The McGill and Walsingham radars were installed with support from the Canada Innovation Foundation and Ontario Innovation Trust. Technical support was provided by G. Carey-Smith, J. Davies, T. Officer, M. van der Zanden and R. van der Zanden. We thank the CSA staff for making facilities at the Canadian Space Agency in Montreal available to us. Assistance and advice regarding the FLEXPART model was provided by O. Cooper, and advice and guidance from W. Komhyr at EN-SCI Corporation was also appreciated.
Author Contributions W.K.H. designed and built all the windprofiler radars used in the studies, and wrote all the on-line radar analysis software. He also originally proposed the concept of using the radars and ozone studies together to investigate stratosphere–troposphere transport, wrote the original proposal, and was the principal investigator on the grant used to obtain the data. T.C.-S. was a post-doctoral fellow on the project, and was responsible for all ozonesonde launches in regard to planning and implementation. He was also responsible for adaptation and implementation of the Flexpart model, and was responsible for data analysis after each flight. D.W.T. was the most experienced of the team in regard to ozone science, and was responsible for the direct supervision of T.C.-S. for significant parts of his tenure. He provided advice about ozonesonde launches and data interpretation, including initiating the use of FLEXPART and GEM to provide a four-dimensional view of the intrusion processes. P.S.A. is a research scientist who co-managed the ozonesonde programme, undertook much of the pre-campaign preparation work, and provided scientific direction during the experimental campaigns. K.S. operated the Toronto Atmospheric Observatory, which was used as a support facility to provide back-up data about the behaviour of various atmospheric chemical constituents. Y.R. supported T.C.-S. with advice. I.Z. and P.A.T., as principal investigators of various windprofiler projects, were responsible for the day-to-day running of the radars.
The file contains Supplementary Methods, Supplementary Table 1 and Supplementary Figure 5
About this article
Atmospheric Science Letters (2018)