Pollen of the common ragweed (Ambrosia artemisiifolia) has higher concentrations of allergen when the plant is exposed to NO2 exhaust gases. A protein that was present in particular when NO2 levels were elevated. This protein was not previously known to be an allergen in Ambrosia, and it has a strong similarity with a protein from a rubber tree. In this context, it was previously described as an allergen whose effect was also known in fungi and other plants. Further experiments related to this topic are currently being planned. Ultimately, it can be expected that the already aggressive Ambrosia pollen will become even more allergenic in the future due to air pollution. Since Ambrosia does not bloom until late summer, it thus lengthens the “season” for allergy sufferers. “After studies have already shown that Ambrosia growing along highways is clearly more allergenic than Ambrosia plants growing away from road traffic, we could provide a reason for this.