• The pollen data can tell us about pollen levels, pollen seasons and the types of pollen in the Minneapolis region.The manufacturer of the Rotorod Sampler used by the Clinical Research Institute, Inc. (CRI) to collect the pollen samples indicates that an appropriately placed sampler provides a measure of airborne pollen for the surrounding 100-150 miles, noting that this distance may be impacted by the presence of geographical factors such as lakes. For more information about the monitor and the collection process, please visit the CRI website.

• Pollen data can be used by allergy and asthma patients to better understand what types of pollen are related to their symptoms during different times of year.
• Analysis of pollen trends over time can inform allergy and asthma patients and their health care providers about the changing climate and what they might expect in the future (e.g., longer pollen seasons).

• These data cannot tell us about pollen levels and trends outside of the 100-150 mile radius surrounding Minneapolis. Depending on the plant and weather conditions, pollen can travel very long distances or distribute close to the source. 

• The pollen is collected and counted by the Clinical Research Institute, Inc. in Minneapolis. The pollen sampler is currently located in south Minneapolis.
• The pollen is collected using a Roto-rod sampler. Daily counts are reported for the previous 24-hour period. The data is typically collected Monday-Friday from March through November.
• Clinical Research Institute, Inc. is a National Allergy Bureau (NAB) certified counting station that adheres to NAB's standardized counting methodology.
• Change in Ragweed Pollen Season (image), 1995–2015. This figure shows how the length of ragweed pollen season changed at 11 locations in the central United States and Canada between 1995 and 2015. Red circles represent a longer pollen season; the blue circle represents a shorter season. Larger circles indicate larger changes. Data source: Ziska et al., 2016

1. Weekly counts by type 

• Each date was assigned a week number using the 2016 calendar. Pollen counts were then calculated by week for 2016 by trees, grasses and weeds. Because counts for trees are substantially higher than for grasses and weeds, tree counts are shown on a different scale. Unidentified weeds were excluded.

2. Length of pollen season by year

• The start date for a pollen season was calculated by summing all daily counts for that year and determining the date on which the 5% of the total count was reached. The end date was calculated by determining the date on which the 95% of the total count was reached. 
• A limitation of this method is that seasons with higher cumulative pollen count will have a shorter calculated season length; the higher the pollen count, the more it constricts the season.

3. Number of days with elevated pollen

• Daily pollen count was calculated and categorized into the National Allergy Bureau (NAB) categories of high and very high, by pollen type. High and very high NAB levels were combined due to fewer very high pollen days. For  more information on the NAB pollen category levels by pollen type.

4. Percent of pollen by type and species

• The percent contribution of each species within a pollen type was calculated. Unknown species were excluded.

• Gaps in the data occurred due to equipment malfunctions. There were periods of missing data in 2003 during tree and grass pollen seasons and incomplete weed pollen data in 2004. Generally, pollen is only collected on weekdays.
• There were more pollen measurements in later years, which can affect some of the pollen metrics. 
• Pollen concentrations are impacted by temperature, wind condition, humidity, and precipitation. The timing of pollen sampling in relation to these meterological events can greatly impact the pollen concentration.
• The biologically relevant radius around a pollen monitor is unknown. The distance where the monitored level of pollen is similar to the actual human exposure is probably less than 5 or 10 miles. 
• These data cannot tell us about pollen levels and trends outside of the 100-150 mile radius surrounding Minneapolis. Pollen is highly localized and can vary even within a city.