Atmospheric deposition is the process by which pollutants and particulate matter present in the atmosphere are transferred to the Earth’s surface, either directly or through precipitation. In stormwater management, atmospheric deposition is an important source of pollutants that accumulate on land surfaces and are later washed off during rainfall events, contributing to stormwater runoff contamination.
Atmospheric deposition occurs in two primary forms, dry deposition and wet deposition. Dry deposition involves the settling of airborne particles, dust, and gaseous pollutants onto surfaces during periods without precipitation. Wet deposition occurs when pollutants are incorporated into rain, snow, sleet, or fog and delivered to the ground as part of a precipitation event. Both forms can deposit a wide range of contaminants, including nutrients such as nitrogen compounds, heavy metals, hydrocarbons, and fine particulate matter.
Once deposited, these pollutants can accumulate on impervious surfaces such as roads, rooftops, and parking lots, as well as on pervious areas like soil and vegetation. During storm events, runoff mobilizes these accumulated materials and transports them into stormwater systems, where they can affect water quality in downstream receiving waters.
Atmospheric deposition is particularly significant in urban and industrial areas, where emissions from vehicles, industrial processes, construction activities, and energy production contribute to higher concentrations of airborne pollutants. It also plays a role in more diffuse, regional pollution issues, as contaminants can be transported long distances in the atmosphere before being deposited.
In stormwater management, atmospheric deposition is considered a nonpoint source of pollution because it originates from widespread, diffuse sources rather than a single discharge point. Understanding its contribution is important for accurately estimating pollutant loads and designing best management practices that address the full range of contaminants entering a stormwater system.