The urban growths in developing countries require new ways of governance since it brings several concerns into focus. Regarding atmospheric properties, air quality imposes serious threats to the tropical urban environment. Health, marginal habitats and livelihoods of urban populations are at risk from pollution, heat stress and sea-level rise. In many of the African countries air pollution inventories are nearly non-existent, pollution is neither monitored nor controlled, and there are no long-term records of pollution levels and impacts. In 2000 the Southern African Air Pollution and Urban Climate Network was formed in order to promote the importance of air quality and climate for the urban environment in Africa. At the moment the network include research groups from Botswana, Mozambique, Kenya, Tanzania and Sweden and the aim is to carry out standardised air pollution and meteorological measurements in the main cities in these countries. The present paper focuses on studies on the urban climate and air quality made in Gaborone, Botswana and Dar es Salaam, Tanzania.

The capital of Botswana, Gaborone is situated in some 100 kilometres south of the tropic of Capricorn. The air quality in Gaborone, a city with roughly 200 000 inhabitants, has been studied in several projects. The air pollution situation in Gaborone is not alarming at the moment but it should be remembered that it is one of the fastest growing cities in Africa. In a pilot study also the urban/rural temperature relationship as well as intra-urban temperature and humidity differences was studied with focus on variations due to building structure and land use. The results showed, in agreement with several other studies in similar climates, a strong urban heat island during wintertime. NOAA NDVI imagery showed that the vegetation index fluctuates far more in rural areas than in the city itself on a seasonal basis. Dry grounds with leafless vegetation are more prone to loose heat than irrigated urban areas, thus increasing the UHI. The observed UHI of 2-3 °C is thought to be higher in winter and lower in summer because of this detected seasonal variation. Large differences in vegetation within the city also contributed to great temperature differences of up to 4 °C as a result of differing evapotranspiration. However, the city as a whole does not act as a cold island at any time of the year.

Dar es Salaam, the major city of Tanzania is a coastal humid tropical city which is roughly ten times larger than Gaborone. Dar es Salaam is heavily polluted and the aim of an ongoing study is to investigate the relationships between urban climate and the air quality. Measurements of particulate matter as well as SO2 and NOX are made at one urban location and at the airport some 15 km outside the city centre. The time resolution is 12 hours, yielding night and day concentrations and sources of the pollutions with TDFXR analysis technique. Data of wind, temperature, humidity, and net radiation from the two sites are compared in order to explain the air pollution situation in the Dar es Salaam region.