Fig. 7 Breakthrough curves of NH⁺₄ and SO^2-₄ at various depths. The 5 mM NH⁺₄ m^-2 and 2.5 mM SO^2-₄ m^-2 were applied after 8 mm of rain, followed by an additional 6 mm of rain. This resulted in a concentration of 360 µM NH⁺₄ and 180 µM SO^2-₄ in the rainwater. The detection limit of NH⁺₄ was 10 µM