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RESEARCH PRODUCT

Northern Hemisphere forests at temperate and boreal latitudes are substantial pollen contributors to atmospheric bioaerosols

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Abstract Forest pollen is a heavy contributor to atmospheric bioaerosols during spring months. This is important because bioaerosols make up 25% of the atmospheric aerosols shaping cloud formation, precipitation and ultimately climate. To test this premise, we drew from available literature, a meta-analysis of 25 forest pollen reports and a comparative analysis of Zea mays versus Pinus taeda pollen. Using available literature, we showed forest pollen grains are not too large or too few in the atmosphere and that some types are prone to bursting into subpollen particles (SPP). High forest pollen concentrations were consistent in the meta-analysis of 25 forest pollen reports from 1937 to 2014 at Northern Hemisphere latitudes ranging from 33°N to 64°N. In eight reports, pollen concentrations exceeded 10 4  grains m −3 for birch ( Betula spp.), spruce ( Picea spp.), pines ( Pinus spp.) and alder ( Alnus spp.). Southern Hemisphere forests had low forest pollen concentrations. Pinus taeda , as a woody perennial species, produced more pollen by three orders of magnitude when compared to Zea mays which serves as the current source of generalized global pollen emissions for general circulation models. Pinus taeda alone accounted for 3.3 Tg y −1 of the world’s current estimate of global pollen emissions although its land area occupies only 0.2% of the world’s forests. Forest pollen, whether intact and burst, is shown here to have the capacity for altitudinal ascent, atmospheric residency and long-distance transport. Thus forest pollen is concluded to be a substantial contributor to atmospheric bioaerosols for higher latitudes during spring in the Northern Hemisphere.