Hi Waldig

> I can see how airborne pollen, in its huge overabundance, ends up in
the nectar

If you open up pollen loads collected from bees at the entrance to the hive and look at the pollen types within the load you can easily find pollen grains of airborne types, in colonies not working these plants for pollen.  I've done this myself and seen grass and nettle pollen at a couple per thousand grains of oilseed rape/canola, fireweed/willowherb or clover, depending on the type of pollen the bee was trying to collect.   At that time of year, these two airborne pollen types are present locally at around 50 pollen grains per cubic metre of air (at the roof of a building) averaged over 24 hours, sometimes several fold higher and often inevitably higher where the bees fly.

Like others, I've also occasionally seen evidence of bees collecting grass or other airborne pollen, but I doubt that this happens regularly in favourable environments or seasons.

The airborne pollen might have settled out on the flowers the bees were visiting, or been collected by impaction or even electrostatic charge on the bee's surface whilst out flying.  Some of that must get into honey, or into pollen storage cells in honey supers.

all the best

Gavin

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