Near-ground effect of height on pollen exposure

Abstract The effect of height on pollenconcentration is not well documented and little is known about the near-ground vertical profile of airborne pollen. This is important as most measuring stations are on roofs, but patient exposure is at ground level. Our study used a big data approach to estimate the near-ground vertical profile of pollenconcentrations based on a global studyof paired stations located at different heights. We analyzed paired sampling stations located at different heights between 1.5 and 50 m above ground level (AGL). This provided pollendata from 59 Hirst-type volumetric traps from 25 different areas, mainly in Europe, but also covering North America and Australia, resulting in about 2,000,000 daily pollenconcentrations analyzed. The daily ratio of the amounts of pollenfrom different heights per location was used, and the values of the lower station were divided by the higher station. The lower station of paired traps recorded more pollenthan the higher trap. However, while the effect of height on pollenconcentration was clear, it was also limited (average ratio 1.3, range 0.7–2.2). The standard deviation of the pollenratio was highly variable when the lower station was located close to the ground level (below 10 m AGL). We show that pollenconcentrations measured at >10 m are representative for background near-ground levels.