| Mike
Newchurch Atmospheric Science Department University of Alabama in Huntsville mike@atmos.uah.edu |
Jae Kim Department of Earth System Science Korea National University of Education jaek@knuecc-sun.knue.ac.kr |
Research supported by
NASA/HQ Atmospheric Chemistry Modeling and Analysis Program
Several methods derive tropospheric ozone from TOMS total (stratosphere + troposphere) ozone column measurements:
(1) Terrain-height difference: Fig 1, Fig 2 [Kim and Newchurch, 1998].
(2) Convective-cloud Differential (CCD): Fig 3 [Ziemke et al., 1998].
(3) Modified Residual: Fig 4 [Hudson and Thompson, 1998; Kim et al., 1996].
(4) Other methods and refinements are in progress.
Tropospheric ozone seasonal variations are well correlated with biomass-burning variations
(1) Downward vertical wind motions cause west-bound air to descend after it passes over the Andes mountains west of Brazil, Fig 5.
(2) The seasonal variation of lower-tropospheric ozone (derived from terrain-height differences) is similar east and west of the Andes and at Natal, Brazil, Fig 6, over New Guinea, Fig 7 and (from the CCD method) in the south Atlantic Fig 8. Highest ozone levels occur in autumn coincident with the burning season.
Trends in tropospheric ozone vary from 0 to 1%/year
(1) Lower-tropospheric ozone trends (from terrain-height difference) west of the Andes average +0.9±0.3%/year, 2s between 10o-23oS and 0%/year elsewhere between 0oN to 37oS, Fig 9. Using Modified Residuals of TTO [Thompson and Hudson, 1998], trends 0-12oS are -1.6±5.6%/year, 2s .
(2) Trends computed from the Natal, Brazil (6oS) ozonesonde record [Logan, 1994], indicate increasing trends of +1 to +2%/year between 800-100 mb, Fig 10. Using Modified Residuals of TTO [Thompson and Hudson, 1998], trends at Natal are -0.2±4.4%/year, 2s .
(3) Using terrain-height differences, trends east of New Guinea (upwind) are 0%/year, trends west of New Guinea (downwind) are +1.0±0.6%/year, 2s , Fig 11.
Tropospheric ozone plumes across the Indian Ocean
(1) Ozonesonde observations west (1987-1990) and east (1995) of Australia consistently measure plumes of ozone in the middle and upper troposphere during Austral spring (~November). The latitudinal variation of integrated tropospheric ozone column ozone is consistent between the sondes, TOMS CCD, and model calculations Fig 12.
(2) MOZART calculations [Emmons et al., 1998; Hauglustaine et al., 1998] present a consistent picture of biomass burning VOCs combined with NOx produced by lightning that results in an ozone plume of 50-60 ppbv, in the middle and upper troposphere, extending from South Africa across the Indian Ocean and Australia into the western Pacific Ocean, Fig 13, 14.
Conclusion
Biomass burning has a significant, long-range effect on tropospheric ozone.