Significant Contribution of Gaseous Organic Nitrogen to Wet and Dry Nitrogen Deposition: Evidence From Year‐Long Monitoring in Coastal Hong Kong

Abstract Atmospheric nitrogen (N) deposition critically affects ecosystem dynamics and carbon cycling, yet organic N (ON) remains under‐monitored relative to inorganic N (IN), limiting constraints on global N budgets and impacts. We conducted year‐long dry and wet deposition measurements of water‐soluble ON (WSON) and IN at a coastal Hong Kong site using an innovative dual‐surface collector, enabling simultaneous dry deposition to pure water and to a quartz filter. Dry deposition to water exceeded that to the filter by 26.6 × (NH 4 + ‐N), 1.6 × (NO 3 − ‐N), and 4.3 × WSON, evidencing strong uptake of water‐soluble gaseous N by the water surface. We provide the first quantification of gaseous versus particulate WSON in dry ON deposition, revealing a dominant gaseous contribution reaching up to ∼80% to the total flux; the higher WSON fraction in wet deposition than in atmospheric particles further implicates gaseous WSON as a key rainwater ON source. Annual total N deposition (wet plus dry deposition‐to‐water) was 39.2 ± 5.2 kg N ha −1 yr −1 , comprising NH 4 + ‐N (31.0 ± 5.0%), NO 3 − ‐N (40.3 ± 5.2%), and WSON (28.7 ± 3.6%). These results demonstrate substantial ON inputs via wet and dry pathways—particularly gaseous—and underscore the need for coordinated measurements of gaseous and particulate ON and IN to better constrain N deposition budgets and ecological impacts.