SEASONAL CHARACTERISTICS OF RAGWEED POLLEN DISPERSAL IN THE UNITED-STATES

Background: The most definitive reports concerning the seasonal charac teristics of ragweed (Ambrosia spp) pollen dispersal in the United Sta tes date back 60 years to work conducted with gravity slide samples. O bjective: Volumetric pollen data from 23 sampling sites were used to s tudy the ragweed pollen season. Methods: The date of first and final p ollen capture and the date with maximum airborne pollen concentration (the ''peak date'') were used to compare the pollen seasons at locatio ns ranging from approximately 30 degrees N to 45 degrees N latitude. R esults: Sixteen cities located north of 38 degrees N possessed similar peak dates (P = 1), generally achieving maximum airborne pollen conce ntration in late August or early September. Four cities located south of 38 degrees N experienced later peak dates, with the most southerly city reaching maximum pollen levels in mid-October. Three cities locat ed in the Northwest did not recover ragweed pollen in air samples. Con clusion: This study confirms earlier reports and suggests what time of year source avoidance is most critical for ragweed sensitive individu als in various locations.