The plot below shows pollen counts in Atlanta, Georgia, USA, in 1999, 2000, 2001, and 2002, as well as highs for the previous years of the 1990s. The data were collected by the Atlanta Allergy Clinic and released via their website. That website indicates that pollen counts over 120 particles per cubic meter are "extremely high".
The plot shows that 1999 and 2002 were very different pollen years. 1999 had several days of very high counts, including the all-time high for Atlanta (6013 particles per cubic meter on April 12, 1999). As was the case in previous years, pine pollen was a major component in the pollen on days of very high counts, and accumulations of yellow-green pollen were visible on cars and pavements. In fact, an 18-car pileup on the Atlanta freeways on April 7, 1999, was blamed on road surfaces made slick by wet pollen after a light rain. 2001 was similarly a year with a major peak in pollen counts, perhaps as the result of significant rain in winter and early spring before a dry spring.
In 2002, on the other hand, pollen counts were never as high as the extreme highs of 1999 and 2001, but counts were higher in late March and late April 2002, so that 2002 was a year of more sustained high counts. Pollen counts in 2000 followed a somewhat similar pattern and may have resulted from drought during the spring of 2000, during which pollen was rarely rained out of the air.
Spring 2003 was an interesting pollen event. The late winter and spring were quite warm: the last time the temperature went below 30°F was February 11, and the last time it went below 25°F was January 28. That seemingly led to a spectacular year of blooming trees and flowers, and to high pollen counts in the first week of April. A new all-time record seemed likely to follow in April's second week. However, rain fell every day in the second week, bringing pollen counts that had approached 5000 down to as low as 24. After those rains, counts rebounded in the third week, but the result was a truncated curve for the year.
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