AN ATMOSPHERIC POLLEN SURVEY CONDUCTED DURING THE WINTER IN MINNEAPOLIS, MINNESOTA, USA

Few atmospheric pollen surveys have been conducted during the winter m onths in cities located in the midlatitudes. The purpose of this prese nt investigation was to study pollen conditions during the winter in M inneapolis, Minnesota, a city that experiences cold temperatures and d evelops substantial snow cover. One hundred thirty-three atmospheric s amples were collected with a Rotorod Sampler between 11 October 1995 a nd 1 May 1996. Pollen was recovered in 109 samples, including 27 of th e 40 samples collected in December and January. Twenty-five types of p ollen were observed during the study period; Cupressaceae (cedar/junip er), Ambrosia (ragweed) and Artemisia (sage/sagebrush) grains were mos t abundant during the period when local plants were not flowering. The weed pollen was most likely contributed by local sources, perhaps by dried flowers on dead plants. In contrast, the Cupressaceae pollen rec overed in October and the early winter months is thought to have origi nated in the southern United Stales where several species of Juniperus flower late in the year. This study demonstrated that low but measura ble concentrations of pollen occurred in the atmosphere throughout the winter.