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

Key findings from this study

This research indicates that:

• Organic nitrogen comprises approximately 29% of total annual nitrogen deposition in coastal Hong Kong, rivaling inorganic nitrogen contributions.
• Gaseous organic nitrogen reaches up to 80% of total organic nitrogen dry deposition flux, establishing it as a dominant pathway previously unquantified by conventional monitoring.
• Water surfaces show substantially higher uptake of gaseous nitrogen species than quartz filters, with water-soluble gaseous ammonium-N showing 26.6-fold greater deposition to water.

Overview

Year-long measurements of nitrogen deposition at a coastal Hong Kong site quantified wet and dry inputs of organic nitrogen (ON) and inorganic nitrogen (IN). An innovative dual-surface collector simultaneously captured dry deposition to pure water and to quartz filters, enabling distinction between gaseous and particulate N species. Results revealed substantial ON contributions through both wet and dry pathways, with gaseous organic nitrogen constituting a previously unquantified major source.

Methods and approach

The study deployed a dual-surface collector over 12 months to measure water-soluble organic nitrogen (WSON) and inorganic nitrogen species. The device collected dry deposition simultaneously on a pure water surface and on a quartz filter, allowing quantification of water-soluble gaseous N uptake. Wet deposition samples were collected alongside dry deposition measurements throughout the monitoring period.

Results

Annual total N deposition reached 39.2 ± 5.2 kg N ha−1 yr−1, comprising nitrate-N (40.3 ± 5.2%), ammonium-N (31.0 ± 5.0%), and WSON (28.7 ± 3.6%). Dry deposition to the water surface exceeded filter-collected deposition by 26.6-fold for ammonium-N, 1.6-fold for nitrate-N, and 4.3-fold for WSON, demonstrating substantial uptake of water-soluble gaseous N by aqueous surfaces.

Gaseous WSON dominated organic nitrogen dry deposition fluxes, comprising approximately 80% of total ON inputs through this pathway. The WSON fraction in wet deposition exceeded that in atmospheric particles, implicating gaseous organic nitrogen as a principal source of rainwater ON. These findings establish gaseous organic nitrogen as a significant yet previously under-measured component of atmospheric N deposition.

Implications

The substantial ON contribution to total N deposition—comprising nearly 29% of annual inputs—indicates that current global nitrogen budgets relying primarily on inorganic N measurements systematically underestimate atmospheric N inputs. Gaseous organic nitrogen constitutes a major deposition pathway previously obscured by conventional sampling methods that capture only particulate species on solid surfaces. This omission constrains understanding of ecosystem nutrient loading and associated effects on carbon cycling in coastal and terrestrial systems.

Coordinated measurement protocols for both gaseous and particulate forms of organic and inorganic nitrogen are necessary to improve regional and global N budget constraints. The relative importance of gaseous ON in coastal environments may reflect regional emissions patterns and warrant investigation in additional geographic settings. Enhanced monitoring of ON speciation will refine predictions of ecosystem responses to nitrogen deposition and support more accurate biogeochemical modeling.

Scope and limitations

This summary is based on the study abstract and available metadata. It does not include a full analysis of the complete paper, supplementary materials, or underlying datasets unless explicitly stated. Findings should be interpreted in the context of the original publication.