The Southern Tropical Atlantic Region Experiment (STARE) Page 2
TRansport and Atmospheric Chemistry near the Equator-Atlantic (TRACE-A) and Southern African Fire/Atmosphere Research Initiative (SAFARI)

Contributed by Meinrat O. Andreae, Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany and Jack Fishman, NASA Langley Research Center, Hampton, Virginia, USA

A Note from the Chair

Science Features
2 BIBEX
3 STARE, TRACE-A, and SAFARI
7 Satellite Fire Monitoring
9 EXPRESSO
11 Domestic vs. Wild Fires in Africa
13 Boreal Forest Fire Research
15 GFMC and BIBEX
16 SAFARI-2000
19 BIBEX in the Future

Regional meteorology and transport of pyrogenic emissions and their reaction products

Meteorological and climatological work in SAFARI was focused on defining the fields of motion at various scales, from the turbulent to the synoptic and planetary, which influence fires and determine the dispersion and transport of pyrogenic emissions. During spring, anticyclonic flow is dominant over the subcontinent south of 15°S, and the atmosphere is characterized by inversions and stable layers that inhibit the development of penetrative moist convection and thus trap pyrogenic material in the lower atmosphere. Once burning products break through the mixed layer they are again trapped by mid-tropospheric stable layers (Garstang et al., 1996). In many instances, smoke laden airmasses in the region were quite old and had recirculated for several days over the continent before being advected to the Indian or Atlantic Oceans (Swap et al., 1996; Tyson et al., 1996). Emission to the Indian Ocean tended to be at higher altitudes, whereas the flow to the Atlantic was usually trapped in the lower few kilometers of the troposphere.

Flights over the tropical South Atlantic were conducted to answer the overriding question of how much of the ozone enhancement is a result of in situ generation and how much is the result of advection from either South America or southern Africa, or both. Photochemical calculations were performed using the in situ DC-8 measurements as input. Calculations near the source regions indicate that photochemical generation of ozone in the lower atmosphere on the regional scale (100-1000 km) near sources of biomass burning are comparable to the amount of regionally generated ozone over industrialized regions at temperate middle latitudes during summertime (Mauzerall et al., 1998).

Table1. "Best guess" emisson factors and emission ratios for savanna fires, and estimates for emissions fromAfrican and global savanna fires, all biomass burning, and all anthropogenic sources (including biomass burning).

Perhaps the most important finding is the ubiquitous nature of ozone generation in the upper tropical troposphere, where integrated ozone production is calculated to be >1 x 1011 mol. cm-2 s-1 between 8-12 km. This large net photochemical production in the upper troposphere offsets the photochemical destruction of ozone within the tropical marine boundary layer. Correlation of NOy with CO suggests that biomass burning was an important source of NOx at all altitudes during TRACE-A. There is also evidence that NOx throughout the TRACE-A region was recycled from its oxidation products rather than directly transported from its primary sources. The low HNO3 mixing ratios observed above 8 km suggest a rapid mechanism of HNO3 to NOx conversion, not usually considered in current models Jacob et al., 1996). Mixing ratios of peroxides and formaldehydes (byproducts of hydrocarbon oxidation and indicators of the oxidizing capacity of the troposphere) were fairly well simulated by the photochemical calculations. Discrepancies between the calculated mixing ratios and ratios among the species point to possible deficiencies in our understanding of the chemical mechanisms by which these compounds are generated in the atmosphere.

Satellite remote sensing of fires and vegetation.

The remote sensing activity in SAFARI-92 was designed to develop and test algorithms for fire detection, to assist in estimating fuel loads, to supply inputs to transport modeling studies, and to assess the potential contribution of satellite data to regional trace gas emission estimates. Most fires were found to occur in the period July-September 1992, with a peak in August, placing the SAFARI-92 field campaign well within the main burning season (Justice et al., 1996). Comparison with a wetter year (1989) showed that burning was reduced by approximately 50 per cent in 1992 in the area between 20° and 30°S, a result ascribed to the effect of the severe drought of 1991/92 on available biomass. A related study (Scholes et al.) reported the development of a method for estimating biomass consumed by fire in the tropics, based on some known fuel-constraining factors and using satellite data to estimate the area burned. The new estimates of the average quantity of biomass burned annually in Africa south of the equator are considerably lower than previous estimates based on extrapolation from point data. These findings highlight the importance of developing new approaches to the measurement of the amounts of biomass burned on a regional scale for future assessments of the environmental impact of biomass burning.

Beyond STARE

The SAFARI-92 campaign in southern Africa was followed by a series of flight missions to characterize the regional atmospheric chemistry outside of the burning season (SA’ARI) and by experiments in Zambia and Kenya (AFARI) to investigate emissions from fires in savanna types which had not been sampled during SAFARI. Studies on soil and plant emissions of trace gases have also continued in the region, to obtain a more comprehensive coverage of ecosystems and soil types, and to understand variability at longer time scales. A future study, SAFARI-2000, is in the planning stage; details can be found later in this newsletter.

In subsequent large-scale atmospheric chemistry studies, a NASA DC-8 mission was conducted in September-October 1996 to investigate the atmospheric chemistry over the tropical Pacific Ocean, which had been assumed a priori be one of the cleanest regions on the planet. A particularly surprising observation, however, was the pervasiveness of biomass burning plumes in the middle troposphere (6-8 km) throughout the southern Pacific region. Initial analysis suggests that many of these plumes, containing unexpectedly high concentrations of O3 and other trace gases associated with emissions from biomass burning, originate from Africa and extend all the way to Easter Island (27°S, 110°W) in the eastern Pacific (Vay et al., 1998). Thus, the impact of burning in the South America and southern Africa truly has a measurable impact on the composition of the atmosphere throughout the entire Southern Hemisphere troposphere.

References

  1. Anderson, B.E., W.B. Grant, G.L. Gregory, E.V. Browell, J.E. Collins, Jr., G.W. Sachse, D.R. Bagwell, C.H. Hudgins, D.R. Blake, and N.J. Blake, Aerosols from biomass burning over the tropical South Atlantic region: Distributions and impacts, J. Geophys. Res., 101, 24117-24138, 1996.
  2. Andreae, M.O., Emissions of trace gases and aerosols from savanna fires, In Fire in the Southern African Savanna: Ecological and Environmental Perspectives, ed. B.W. van Wilgen, M.O. Andreae, J.G. Goldammer, and J.A. Lindesay, pp. 161-183, Witwatersrand University Press, Johannesburg, South Africa, 1997.
  3. Blake, N.J., D.R. Blake, B.C. Sive, T.Y. Chen, F.S. Rowland, J.E. Collins, G.W. Sachse, and B.E. Anderson, Biomass burning emissions and vertical distribution of atmospheric methyl halides and other reduced carbon gases in the South Atlantic region, J. Geophys. Res., 101, 24151-24164, 1996.
  4. Browell, E.V., M.A. Fenn, et al., Ozone and aerosol distributions and air mass characteristics over the South Atlantic basin during the burning season, J. Geophys. Res., 101, 24043-24068, 1996.
  5. Cachier, H., C. Liousse, M.-H. Pertuisot, A. Gaudichet, F. Echalar, and J.P. Lacaux, African fire particulate emission and atmospheric influence, in Biomass Burning and Global Change, ed. J.S. Levine, pp. 428-440, MIT Press, Cambridge, Mass., 1996.
  6. Fishman, J., C.E. Watson, J.C. Larsen, and J.A. Logan, Distribution of tropospheric ozone determined from satellite data, J. Geophys. Res., 95, 3599-3617, 1990.
  7. Garstang, M., P. D. Tyson, R. Swap, M. Edwards, P. Kållberg, and J.A. Lindesay, Horizontal and vertical transport of air over southern Africa, J. Geophys. Res., 101, 23721-23736, 1996.
  8. Gregory, G.L., H.E. Fuelberg, S.P. Longmore, B.E. Anderson, J.E. Collins, Jr,, and D.R. Blake, Chemical characteristics of tropospheric air over the tropical South Atlantic Ocean: Relationship to trajectory history, J. Geophys. Res., 101, 23957-23972, 1996.
  9. Harris, G.W., F.G. Wienhold, and T. Zenker, Airborne observations of strong biogenic NOx emissions from the Namibian savanna at the end of the dry season, J. Geophys. Res., 101, 23707-23712, 1996.
  10. Heikes, B., M. H. Lee, D. Jacob, R. Talbot, J. Bradshaw, H. Singh, D. Blake, B. Anderson, H. Fuelberg, and A. M. Thompson, Ozone, hydroperoxides, oxides of nitrogen, and hydrocarbon budgets in the marine boundary layer over the South Atlantic, J. Geophys. Res., 101, 24221-24234, 1996.
  11. Jacob, D.J., B.G. Heikes, S.-M. Fan, J.A. Logan, D.L. Mauzerall, J. D. Bradshaw, H.B. Singh, G.L. Gregory, R.W. Talbot, D.R. Blake, and G.W. Sachse, The origin of ozone and NOx in the tropical troposphere: A photochemical analysis of aircraft observations over the South Atlantic basin, J. Geophys. Res., 101, 24235-24250, 1996.
  12. Jury, M.R., E. Brunke, and M. Schormann, Aircraft section measurements of meteorology and ozone in northern Namibia during SAFARI-92, J. Geophys. Res., 101, 23713-23720, 1996.
  13. Justice, C.O., J. D. Kendall, P.R. Dowty, and R. J. Scholes, Satellite remote sensing of fires during the SAFARI campaign using NOAA advanced very high resolution radiometer data, J. Geophys. Res., 101, 23851-23864, 1996.
  14. Kirchhoff, V.W. J.H., and P.C. Alvalá, Overview of an aircraft expedition into the Brazilian cerrado for the observation of atmospheric trace gases, J. Geophys. Res., 101, 23973-23982, 1996.
  15. Koppmann, R., A. Khedim, J. Rudolph, D. Poppe, M. O. Andreae, G. Helas, M. Welling, and T. Zenker, Emissions of organic trace gases from savanna fires in southern Africa during the 1992 Southern African Fire Atmosphere Research Initiative and their impact on the formation of tropospheric ozone, J. Geophys. Res., 102(D15), 18879-18888, 1997.
  16. Lacaux, J.-P., R. Delmas, C. Jambert, and T.A. J. Kuhlbusch, NOx emissions from African savanna fires, J. Geophys. Res., 101, 23585-23596, 1996.
  17. Le Canut, P., M.O. Andreae, G.W. Harris, F.G. Wienhold, and T. Zenker, Aerosol optical properties over southern Africa during SAFARI-92, In Biomass Burning and Global Change, ed. J.S. Levine, pp. 441-459, MIT Press, Cambridge, Mass., 1996.
  18. Levine, J.S., E.L. Winstead, D.A. B. Parsons, M.C. Scholes, R.J. Scholes, W.R. Cofer, III, D.R. Cahoon, Jr., and D.I. Sebacher, Biogenic soil emissions of nitric oxide (NO) and nitrous oxide (N2O) from savannas in South Africa: The impact of wetting and burning, J. Geophys. Res., 101, 23689-23697, 1996.
  19. Maenhaut, W., I. Salma, J. Cafmeyer, H.J. Annegarn, and M.O. Andreae, Regional atmospheric aerosol composition and sources in the Eastern Transvaal, South Africa, and impact of biomass burning, J. Geophys. Res., 101, 23631-23650, 1996.
  20. Mauzerall, D.L., J.A. Logan, D.J. Jacob, B.E. Anderson, D.R. Blake, J.D. Bradshaw, B. Heikes, G.W. Sachse, H. Singh, and B. Talbot, Photochemistry in biomass burning plumes and implications for tropospheric ozone over the tropical South Atlantic, J. Geophys. Res., 103(D7), 8401-8423, 1998.
  21. Pickering, K.E., A.M. Thompson, Y. Wang, W.-K. Tao, D.P. McNamara, V.W.J.H. Kirchhoff, B. G. Heikes, G.W. Sachse, J. D. Bradshaw, G.L. Gregory, and D.R. Blake, Convective transport of biomass burning emissions over Brazil during TRACE A, J. Geophys. Res., 101, 23993-24012, 1996.
  22. Scholes, R.J., J. Kendall, and C.O. Justice, The quantity of biomass burned in Southern Africa, J. Geophys. Res., 101, 23667-23676, 1996.
  23. Singh, H.B., D. Herlth, et al., Impact of biomass burning emissions on the composition of the South Atlantic troposphere: Reactive nitrogen and ozone, J. Geophys. Res., 101 (D19), 24203-24219, 1996.
  24. Smyth, S.B., S.T. Sandholm, J.D. Bradshaw, R.W. Talbot, D.R. Blake, N.J. Blake, F.S. Rowland, H.B. Singh, G.L. Gregory, B.E. Anderson, G.W. Sachse, J.E. Collins, and A.S. Bachmeier, Factors influencing the upper free tropospheric distribution of reactive nitrogen over the South Atlantic during the TRACE-A experiment, J. Geophys. Res., 101, 24165-24186, 1996.
  25. Swap, R., M. Garstang, S.A. Macko, P.D. Tyson, W. Maenhaut, P. Artaxo, P. Kållberg, and R. Talbot, The long-range transport of southern African aerosols to the tropical South Atlantic, J. Geophys. Res., 101, 23777—23792, 1996.
  26. Talbot, R. W., J.D. Bradshaw, et al., Chemical characteristics of continental outflow over the tropical South Atlantic Ocean from Brazil and Africa, J. Geophys. Res., 101, 24187-24202, 1996.
  27. Thompson, A.M., K.E. Pickering, D.P. McNamara, M.R. Schoeberl, R.D. Hudson, J.-H. Kim, E.V. Browell, V.W.J.H. Kirchhoff, and D. Nganga, Where did tropospheric ozone over southern Africa and the tropical Atlantic come from in October 1992? Insights from TOMS, GTE TRACE-A, and SAFARI 1992, J. Geophys. Res., 101, 24251-24278, 1996.
  28. Tyson, P.D., M. Garstang, R. Swap, P. Kållberg, and M. Edwards, An air transport climatology for subtropical southern Africa, Internat. J. Climatol., 16, 16265-16291, 1996.
  29. Vay, S.A., B. E. Anderson, T.J. Conway, G.W. Sachse, J.E. Collins, Jr., D.R. Blake, and D.J. Westberg, Airborne observations of the tropospheric CO2 distribution controlling factors over the South Pacific basin, J. Geophys. Res., 1998, in press.
  30. Zenker, T., A.M. Thompson, D.P. McNamara, T.L. Kuscera, G.W. Harris, F.G. Wienhold, P. Le Canut, M.O. Andreae, and R. Koppmann, Regional trace gas distribution and airmass characteristics in the haze layer over southern Africa during the biomass burning season (Sep./Oct. 92): Observations and modeling from the STARE/SAFARI'92/DC-3, In Biomass Burning and Global Change, ed. J.S. Levine, pp. 296-308, MIT Press, Cambridge, Mass., 1996.
  31. Zepp, R.G., W.L. Miller, R.A. Burke, D.A.B. Parsons, and M.C. Scholes, Effects of moisture and burning on soil-atmosphere exchange of trace carbon gases in a southern African savanna, J. Geophys. Res., 101, 223699-23706, 1996.