Preliminary results of dry-season trace gas and aerosol measurements over the Kalahari region during SAFARI 2000 D. C. Stein % *, R. J. Swap % , S. A. Macko % , S. J. Piketh w , B. Doddridge z & R. Bruintjes } % Department of Enviromental Sciences, University of Virginia, Clark Hall, P.O. Box 400123, Charlottesville, VA 22904-4123, U.S.A. wClimatology Research Group, University of Witwatersrand, Private Bag 3, 2050 Wits, Johannesburg, South Africa wUniversity of Maryland, Department of Meteorology, Computer and Space Science Building, College Park, MD 20742, U.S.A. }Research Applications Programme, National Center for Atmospheric Research, P.O. Box 3000, Boulder, 10,80307-3000, U.S.A. (Received 22 July 2002, accepted 22 July 2002) Trace gas and aerosol data were collected through a series of flights over the arid Kalahari Makgadikgadi Pan system. These data show statistically significant spatial and temporal variations in ozone concentrations, while SO 2 concentra- tions were found to be relatively constant. Transport and photochemical production processes are two possible mechanisms for the observed temporal variation in ozone concentration. The presence of certain types of vegetation that emit ozone-precursor gases may account for some of this spatial variation. Aerosols may also be formed as a result of the gases emitted. These species of vegetation alter atmospheric chemistry characteristics and influence the climate. In arid regions, the presence of trace gases and aerosols has an important effect on radiation budget and cloud formation processes, which are significant controlling factors of climate. This paper is a first attempt to synthesize the relationship between surface ecology and atmospheric chemistry of arid environments to better understand the regional climate. # 2003 Elsevier Science Ltd. Keywords: volatile organic compounds (VOC); air quality; ozone formation; botswana; sua pan Introduction Results from the Southern African Fire-Atmosphere Research Initiative (SAFARI-92) suggested that biogenic emissions from both vegetative and microbial sources could *Corresponding author. Fax: +1-484-924-4761; E-mail: dcs5v@virgina.edu 0140-1963/03/020371 + 09 $35.00/0 # 2003 Elsevier Science Ltd. Journal of Arid Environments (2003) 54: 371–379 doi:10.1006/jare.2002.1096