Evaluation of hirst-type sampler and PM10 impactor for investigating adhesion of atmospheric particles onto allergenic pollen grains

Abstract

Hirst-type sampler (HTS) is the standard equipment for pollen sampling while cascade impactors are commonly used for particulate matter (PM) samplings. In this work, we investigated the feasibility of using such devices to reliably assess the atmospheric PM adhesion onto pollen grains (PGs). Birch PGs were deposited on sampling substrates and then exposed to ambient PM in each type of sampling device operating simultaneously. In the HTS, the surface of PGs was significantly polluted with PM during sampling (93.5% of polluted PGs with on average 4 particles per PG with a mean diameter of 2.2 µm). A modified entrance slit was tested and proved to significantly reduce the PM sampling artifact (28% of polluted PGs), although not completely canceling it. In contrast, in the PM10 impactor, all PGs remained free from particulate pollutants. We concluded that the PM pollution of PGs reported in previous studies using a HTS may be overestimated. While PG samplings using a HTS might provide insights into the co-exposure to allergenic pollen and other ambient PM, a size-selective aerosol sampler proves to be more appropriate for a reliable assessment of the extent of PM pollution of airborne pollen in order to give a realistic depiction of the physical and chemical state of ambient PGs that could be inhaled.