Light Rain Enhances Sulfate, Nitrate, and Ammonium Wet Deposition Hysteresis to Their Precursor Emission Controls

Sulfur and nitrogen wet deposition is governed by anthropogenic emissions and precipitation regimes. However, the impacts of precipitation characteristics on wet deposition SO 4 2− , NO 3 − and NH 4 + and its hysteresis to precursor emission controls remain inadequately quantified. Multiyear (2010–2024) rainwater chemistry, air pollutants, and meteorological parameters were monitored in Wuhan. Random forest models were applied to weather‐normalized sulfur and nitrogen wet deposition. Trend analysis using the normalized data revealed that 1‐unit reduction in precursor emissions declined 0.14–0.48‐unit sulfur and nitrogen wet deposition. This hysteresis was driven partly by enhanced wet scavenging associated with increased light rain frequency, as the scavenging ratios of atmospheric sulfur and nitrogen compounds increased by 1.9%–10.5% yr −1 from 2016 (2019) to 2024. Light rain with a rate ≤16.5, 17.3, and 6.8 mm d −1 most strongly influenced wet deposition trends of NH 4 + , NO 3 − , and SO 4 2− , respectively, identified by the SHapley Additive exPlanations approach. The light rain frequency rose by 2.6%–3.7% yr −1 during 2010–2024, annually adding 0.036 kg N ha −1 yr −1 to nitrogen deposition since 2010 and 0.003 kg S ha −1 yr −1 to sulfur deposition since 2014. This study demonstrates how light rain critically governs atmospheric sulfur and nitrogen source‐sink dynamics amid shifting emissions and climates.