It's not just the quantity of pollen that's a problem. It can also be the diversity - and that isn't helped by invasive species.

You can read the blog post at: https://botany.one/2022/05/research-from-germany-discovers-why-your-pollen-allergies-might-be-getting-worse/

You can read the original research at: https://doi.org/10.1007/s13280-022-01741-z