Waisel et al. 2004. Authors established threshold levels for airborne pollen resulting in symptoms for atopics in an Israeli village based on once a week air sampling, SPT, and self-reported symptom diaries. For these subjects, threshold levels in pollen grains/m³ were 2-4 for olive, 3-5 for grasses, 4-5 for Artemesia, 10-20 for pecan, 50-60 for cypress.