A comparative study of the atmospheric pollen content in two cities, located at similar latitudes, though in different continents, was undertaken. Special consideration was given to the meteorological determinants as shown by correlation analyses. In both localities, the contribution of Poaceae to the aerospora was quite distinct and varied from year to year. Analyses were carried out taking into account either years or cities separately or combined, and at two time scales: daily or weekly counts. Maximum temperature was the major meteorological determinant for daily grass pollen concentration values. Owing to its more arid climate, grass populations in Leon seem to react more to sunshine hours. Relative humidity and precipitation had a negative influence but at different time scales in the two localities. In Leon, they are related to everyday events such as convective storms, while in Montreal, the same events are related to low-pressure systems that have the same time scale as air masses. We found that wind speed was the only factor that acted differently in Montreal and Leon. In Leon, wind speed has the well-known dilution impact, while in Montreal, it has a positive impact by increasing pollen shedding from the anthers. Wind speed has therefore a stronger influence at two different stages of the areobiological pathway in both localities.
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