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NAB Home My NAB Levels Level Resources NAB Resources Contact the NAB Donate to the AR Trust		NAB: Reading the Charts The following Aeroallergen Network calculations are based on the data (per cubic meter) reported by all certified counting stations for trees, grasses, weeds and molds. Median or 50th percentile (half of counts are below this point) 75th percentile (75% of counts are below this point) 99th percentile (99% of counts are below this point) Based on these calculations, we suggest the following definitions for low, moderate, high and very high concentration levels: NAB SCALE * MOLD 0 Absent 1 - 6499 Low 6500 - 12999 Moderate    13000 - 49999 High >50000 Very High GRASS 0 Absent 1 - 4 Low 5 - 19 Moderate    20 - 199 High >200 Very High TREE 0 Absent 1 - 14 Low 15 - 89 Moderate    90 - 1499 High >1500 Very High WEED 0 Absent 1 - 9 Low 10 - 49 Moderate    50 - 499 High >500 Very High * These mold levels were determined based on outdoor exposure to natural occurring spores in the environment and should not be applied to indoor exposure which may represent an entirely different spectrum of spore types. These definitions would allow comparison between sites across the country. They are based on ecological measurements, not health effects. However, assuming dose/response relationships are the same across the country, the definitions are probably more appropriate than a definition based on local numbers. This does mean that, for some stations, some categories will never be high.
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