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



Tropospheric ozone is of considerable environmental importance as a major greenhouse gas, as the primary source of OH radicals, and as a pollutant that damages human health and vegetation. Ozone is produced in the troposphere by photochemical oxidation of CO and volatile organic compounds (VOCs) in the presence of nitrogen oxides (NOx). The chemistry is complicated and highly nonlinear, and coupled to transport on all scales, so that understanding of the factors controlling ozone is difficult. For example, there is no satisfactory explanation for the persistent rise in the tropospheric ozone background observed in the northern hemisphere over the past several decades. Recent satellite observation capabilities from TES, MLS, GOME, and OMI provide for the first time a global continuous data set for tropospheric ozone. We are analyzing data from TES, MLS, and OMI together with correlative information to gain new insights into the mechanisms controlling ozone.


  • Use satellite observations of tropospheric ozone and its correlations with other gases to improve understanding of the factors controlling ozone concentrations;
  • Assess the implications for the influence of human activity and climate change.


  • Evaluate TES tropospheric ozone with in situ observations from ozonesondes;
  • Analyze spatial distributions and interannual variations in TES and MLS ozone and CO:
  • Intercompare tropospheric ozone observations from TES, OMI;
  • Evaluate global model simulations (GEOS-Chem and GMI) of tropospheric ozone using TES and MLS observations and assess the sensitivity to different sources and processes.


  • TES ozone (V002) is biased high by 3-10 ppb in the upper and lower troposphere
  • TES data show large differences in CO, O3, and H2O over Indonesia and the eastern Indian Ocean in Oct.-Dec. 2006 relative to 2005.  In 2006, O3 was higher by 15-30 ppb; CO was higher by >80 ppb in Oct.-Nov., and by ~25 ppb in Dec. 
  • The high CO in 2006 was caused by increased biomass burning in Indonesia during the El Niño/Indian Ocean Dipole (IOD) induced drought.
  • In the region of highest CO (~200 ppb), the fires contributed ~45% to enhanced O3 in October, ~75% in early November, and only 10% in December.
  • More lightning in late 2006 compared to 2005 caused an increase in O3 of a few ppb. 
  • Dynamical changes increaseO3 over a larger region than fire emissions which mainly increase O3 at 10ºN-10ºS in October and November.  
  • The model underestimate of the O3 anomaly in November and December is ascribed to overly active convection in the model in late 2006, based on an analysis of Outgoing Longwave Radiation (OLR) data.
  • An underestimate of NOx emissions from soils may also contribute to the disparity at the end of the year. 
  • A dramatic decrease  in O3 in late 2006 in equatorial Africa and the western Indian Ocean is reproduced by the model and is caused by highly enhanced convection in 2006, likely associated with the IOD.

PEOPLE: Ray Nassar, Lin Zhang, Jennifer Logan

COLLABORATORS: Nathaniel Livesey (JPL), Helen Worden (NCAR), Kevin Bowman, Ming Luo (NASA/JPL), Dylan Jones (U. Toronto)


  • Livesey, N. J., J. A. Logan, M. L. Santee, J. W. Waters, R. M. Doherty, W. G. Read, L. Froidevaux, and J. H. Jiang, Interrelated variations of O3, CO and deep convection in the tropical/subtropical upper troposphere observed by the Aura Microwave Limb Sounder (MLS) during 2004-2011, Atmos. Chem. Phys., 13, 579-598, 2013. [PDF]
  • Nassar, R., J. A. Logan, I. A. Megretskaia, L. T. Murray, L. Zhang, and D. B. A. Jones (2009). Analysis of tropical tropospheric ozone, carbon monoxide and water vapor during the 2006 El Niño using TES observations and the GEOS-Chem model,J. Geophys. Res., 114, D17304, doi:10.1029/2009JD011760, 2009. [PDF]
  • Nassar, R., J. A. Logan, H. M. Worden, et al. (2008), Validation of Tropospheric Emission Spectrometer (TES) Nadir Ozone Profiles Using Ozonesonde Measurements,J. Geophys. Res., 113, D15S17,doi:10.1029/2007JD008819. [PDF]
  • Logan, J. A., I. Megretskaia, R. Nassar, L. T. Murray, L. Zhang, K. W. Bowman, H. M. Worden, and M. Luo, The effects of the 2006 El Niño on tropospheric composition as revealed by data from the Tropospheric Emission Spectrometer, Geophys. Res. Lett., 35, L03816, doi:10.0129GL031698, 2008. [PDF]
  • Worden, H. M., J. A. Logan, et al. (2007), Comparisons of Tropospheric Emission Spectrometer (TES) ozone profiles to ozonesondes: methods and initial results, J. Geophys. Res., 112, D03309, doi:10.1029/2006JD007258. [PDF]