Indicator # 2 - Date when the pollen season ended by pollen source             Print PDF

Pollen Risk Communication Message: Pollen grains are released by trees in the spring, different types of grass in summer and a variety of weeds in fall.  Ragweed pollen is also released in the fall, but it is more allergenic than other pollen types.  Because of climate variability we now know that higher temperatures and more carbon dioxide result in increased pollen in the air.  Children and older adults who have asthma, allergic rhinitis or other respiratory diseases have more severe allergic reactions as total pollen grains in the air increase or when ragweed pollen is produced in the fall.  Pollen influenced allergic and respiratory reactions are even worse in the summer when ozone and/or fine particulates in the air are also higher.  Research has shown that higher pollen levels increase emergency department visits and inpatient hospitalizations due to asthma, hay fever and other respiratory diseases.  Prevention efforts can include seeing a health care provider before the start of the pollen season or when breathing problems become worse when pollen spores increase.  Persons can decrease their exposure to pollen by not going outdoor, staying in a home or automobile with the windows closed and the air conditioner on, taking a shower to remove pollen from around the nose and mouth, and changing clothes.  For more information about pollen and health see the MTN pollen indicator page.

 Data sources for this indicatorà

  • Determine the last day, also recorded as mm/dd/yyyy, in which counting took place for any pollen source in the calendar year.
  • The end of the pollen season should be recorded for the four pollen sources, trees, grasses, weeds, and ragweed, separately.
  • Note: If a pollen station makes pollen readings throughout the calendar year, the last day should be December 31. Likewise, if the last pollen reading was made on a date prior to December 31, then record on that date as the end date for the pollen season.




Table: End date of pollen source by year.


  1997 1998 1999 2000 2001 2002 2003 2004
Total 11-Jun 27-May 21-May 11-Jul 31-May 3-Jun 3-Jun 25-May
Tree 9-Jun 18-May 21-May 15-May 31-May 1-Jun 5-Jun 13-May
Grass 9-Sep 25-Jun 10-Jun 4-Oct 4-Oct 21-Sep 30-Jun 6-Sep
Weed 28-Oct 30-Sep 21-Sep 22-Sep 13-Oct 7-Oct 15-Oct 13-Oct
Ragweed 28-Oct 30-Sep 21-Sep 4-Oct 13-Oct 7-Oct 14-Oct 27-Sep

  2005 2006 2007 2008 2009 2010 2011 2012
Total 7-Sep 22-May 15-May 15-May 21-May 11-May 13-May 3-Sep
Tree 6-Jun 22-May 15-May 15-May 18-May 11-May 13-May 11-May
Grass 15-Sep 13-Sep 4-Sep 5-Sep 5-Jun 11-Jun 13-Jun 3-Sep
Weed 11-Oct 5-Oct 3-Oct 26-Sep 24-Sep 21-Sep 30-Sep 20-Sep
Ragweed 11-Oct 27-Sep 3-Oct 24-Sep 18-Sep 23-Sep 30-Sep 20-Sep