Background: The objective of the present work was to compare pollen counts at three different urban locations within a city to each other and to the counts from a fixed trap. This information could be useful to delimit zones in the urbanized part of the city according to the risk of allergic affections.

Methods: Aerobiological sampling using portable traps was carried out at three points in urban zones of the city of Badajoz (SW Spain) over one year at the same time as continuous sampling using a fixed trap at a point in the nonurban outskirts of the city. The sources of airborne pollen were studied by counting the trees in the streets and
squares of the selected zones. A statistical analysis was performed of the differences between the portable and fixed traps and of the temporal and spatial variation in the city as a function of the distribution of the most important pollen sources.

Results: Forty-eight pollen types were identified with the fixed trap, and 28 with the portable traps. The grass, olive, and oak pollens come from almost exclusively external sources, there being no spatial differences in their concentrations in the city. Cypress pollen concentrations were much higher at the urban locations than at the fixed
trap site. Plane tree pollen levels could be locally very high, reflecting the proximity of the source. Except for ornamental plants, pollen levels were lower at the urban locations than at the site on the outskirts of the city.

Conclusions: 1) Using portable traps at different urban zones in a city could provide information about the spatial variation of atmospheric pollen levels. 2) A knowledge of the often widely variable distribution of ornamental plants with potentially allergenic pollen could be useful in indicating city zones with a greater or lesser incidence of potential pollinosis.

Key words: aerobiology, air sampling, allergens, outdoor, pollen, portable traps.