Jennifer A. Logan
Senior Research Fellow
School of Engineering and Applied Sciences
Harvard University



Stratospheric ozone decreased at northern mid-latitudes between the end of the 1970s and the mid-1990s.  More recently, ozone levels have leveled off in the lower stratosphere, 12-25 km.  The main sources of information on trends in the vertical distribution of ozone are balloon-borne sounding (ozonesondes), and satellite data.  We examined the consistency of the long-term records of ozonesondes and three satellite instruments, SAGE II, HALOE, and SBUV (a newly released data set).

Our results were used in the Scientific Assessment of Ozone Depletion: 2010 [PDF], as well as in previous the Assessment Reports for 2006, 2002 and 1998.

Long-term (25 year) trends in tropospheric ozone profile averaged over the northern extratropics are essentially zero.  However, the trends vary regionally, and with the particular time considered, as summarized in Chapter 3 of the 2006 Assessment.

We analyzed trends in multiple data sets for tropospheric ozone over Europe, where there are more long time series os measurements than anywhere else in the world. However, they do not become self-consistent until the late 1990s (Logan et al., 2012).


  • Compare time series of 4 datasets (sondes, SAGE II, HALOE, and SBUV(/2)) and evaluate effects of different sampling
  • Evaluate the V8 SBUV(/2) time series derived from 4 sensors with SAGE II data
  • Compare trends derived from sondes, SAGE II and SBUV(/2)
  • Examine the contribution of stratopsheric ozone to interannual variability of tropospheric ozone
  • Evaluate the consistency of sonde, MOZAIC, and alpine data sets for tropospheric ozone over Europe


  • Ozone in the past few years is ~6% below values in the early 1980s for 18-27 km.
  • Trends and interannual variability (IAV) from sondes, SAGE II, HALOE, and SBUV(/2) agree for 20-30 km  over Europe
  • Sonde, SAGE and HALOE data agree well for 12-30 km
  • Small differences between sonde and SAGE time series and trends are caused by spatial and temporal sampling differences
  • Most biases between SAGE II and SBUV(/2) are within ±10%
  • There are inhomogeneities in the SBUV(/2) time series in the upper stratosphere, that cause the SBUV(/2) to give more positive trends than SAGE II
  • Tropospheric ozone at ~3 km over Europe has been decreasing since the late 1990s.


  • Logan, J.A., et al., Changes in ozone over Europe: analysis of ozone measurements from sondes, regular aircraft (MOZAIC) and alpine surface sites, J. Geophys. Res., 117, D09301, doi:10.1029/2011JD016952, 2012. [PDF]
  • Terao, Y., J. A. Logan, A. R. Douglass, and R. S. Stolarski, Contribution of stratospheric ozone to the interannual variability of tropospheric ozone in the northern extratropics, J. Geophys. Res., 113, D18309, doi:10.1029/2008JD009854, 2008. [PDF]
  • Terao, Y., and J. A. Logan, Consistency of time series and trends of stratospheric ozone as seen by ozonesondes, SAGE II, HALOE, and SBUV(/2), J. Geophys. Res. 112, D06310, doi:10.1029/2006JD007667, 2007. [PDF]


Cunnold, D. M., H. J. Wang, L. Thomason, J. Zawodny, J. A. Logan and I. A. Megretskaia, SAGE (v.5.96) ozone trends in the lower stratosphere, J. Geophys. Res., 105, 4445-4457, 2000.

Logan, J.A., I. A. Megretskaia, A. J. Miller, et al., Trends in the vertical distribution of ozone: a comparison of two analyses of ozonesonde data, J. Geophys. Res., 104, 26373-26399, 1999. [PDF]

Randel, W. J., R. S. Stolarski, D. M. Cunnold, J. A. Logan, M. J. Newchurch, and J. Zawodny, Trends in the vertical distribution of ozone, Science, 285, 1689-1692, 1999.

Logan, J. A., Trends in the vertical distribution of ozone: An analysis of ozonesonde data, J. Geophys. Res., 99, 25553-25585, 1994. [PDF]

Logan J. A., Tropospheric ozone: seasonal behavior, trends and anthropogenic influence. J. Geophys. Res., 90, 10,463-10,482, 1985.