Large concentrations of pollen from the air can result in allergic reaction that spread for miles, even indoors. The weed that causes 75 per cent of all hay fever is ragweed that has a lot of species. A person ragweed plant is estimated to provide around 1 billion pollen grains. https://pollenmesh01029.ziblogs.com/30437868/a-simple-key-for-pollen-mesh-unveiled