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Watershed DepositionTool

Background

Atmospheric wet and dry deposition can be important contributors to total pollutant loadings in watersheds. Since deposition can be expensive to monitor over an entire watershed, estimates of deposition are often obtained from regional scale air quality models such as the EPA/NOAA’s regional-scale, multi-pollutant Community Multiscale Air Quality model (CMAQ). CMAQ can be used to estimate deposition resulting from a number of scenarios including current conditions and future emissions reductions that are expected due to rules such as Clean Air Interstate Rule (CAIR) and Clean Air Mercury Rule (CAMR). CMAQ produces gridded output with typical grid sizes of 36, 12, and 4 km. Since watersheds do not conform to the grid layout of CMAQ, additional tools must be used to map the results from CMAQ to the watersheds to provide the linkage between air and water needed for TMDL (Total Maximum Daily Load) and related nonpoint-source watershed analyses. This linkage then allows water quality management plans to include the reductions in atmospheric deposition produced by the air regulatory community in their calculation of loadings to the watershed.

Overview of the Watershed Deposition Tool

The Watershed Deposition Tool (WDT) was developed by the Atmospheric Modeling Division to provide an easy to use tool for mapping the deposition estimates from CMAQ to watersheds to provide the linkage between air and water needed for TMDL (Total Maximum Daily Load) and related nonpoint-source watershed analyses. This software tool takes gridded atmospheric deposition estimates from NOAA/EPA’s regional, multi-pollutant air quality model, CMAQ, and allocates them to 8-digit HUC’s (hydrologic cataloging units of rivers and streams) within a watershed, State or Region. The WDT can calculate the weighted average CMAQ atmospheric deposition (wet, dry, wet + dry) across a selected HUC or a set of selected HUC’s for a given scenario. The WDT can also calculate the average change in air deposition across a HUC between two different air deposition simulations. Calculations can be exported to CSV files. For experienced GIS users the WDT can also export GIS Shape files of the CMAQ gridded outputs. The tool is designed to work under the Microsoft Windows system.

Deposition Components Available from CMAQ

• Nitrogen
• Dry Oxidized Nitrogen
• Wet Oxidized Nitrogen
• Total (Wet+Dry) Oxidized Nitrogen
• Dry Reduced Nitrogen
• Wet Reduced Nitrogen
• Total (Wet + Dry) Reduced Nitrogen
• Total Dry (Reduced + Oxidized) Nitrogen
• Total Wet (Reduced + Oxidized) Nitrogen
• Total (Reduced + Oxidized) Nitrogen
• Sulfur
• Total Wet Sulfur
• Total Dry Sulfur
• Total (Wet + Dry) Sulfur
• Mercury
• Total Wet Mercury
• Total Dry Mercury
• Total (Wet + Dry)Mercury

Download the Watershed Deposition Tool (vs 1.4.13)

Available CMAQ files

Major species: Major species included in the file. N – Nitrogen; S – Sulfur; Hg – Mercury

Met year/type: Year of meteorology used in the run. “Agg” refers to a special dataset where CMAQ was run for 3 years (2001-2003) of meteorological data including a “dry”, “wet”, and “average” year. Deposition values in this dataset represent a climatologically averaged deposition for the eastern half of the US (relative to 30-year average precipitation).

Grid Res: Grid resolution for the data. 36con – 36 km continental domain; 12con – 12 km continental domain; 12e – 12 km eastern domain;

CMAQ version: indicates the version of CMAQ used in the run.
cctmJ4f – CMAQ v4.5

cctm43m – CMAQ v4.3 with updated mercury chemistry

Chem mech: chemical mechanism used in CMAQ. sp99 = SAPRAC 1999; cb04 = Carbon Bond 4

BEIS version: version of the Biogenic Emission Inventory System (BEIS) used

NH3 emiss: NH3 emission adjustment.

nh3c1 = Chesapeake Bay factor set version 1;
nh3g2 = Gilliland, A.B., K.W.Appel, R.Pinder, S.J.Roselle, and R.L.Dennis, Seasonal NH3 emissions for an annual 2001 CMAQ simulation: inverse model estimation and evaluation, Atmospheric Environment, 4986-4998. 2006

Bias adjust: na = not adjustment; wa = deposition adjusted for wet deposition bias. The bias adjustment principally affects nitrate wet deposition, which is biased low in the summer season. The adjustment would be applied for each season and for the annual wet deposition.

Emissions scenario: indicates whether results are for a base case (2001) or future projection. 2010cair: emissions are for the 2010 CAIR+CAMR+BART futures projection, representing the sum total of these regulations + mobile source regulations on 2010 emissions; 2020cair: emissions are for the 2020 CAIR+CAMR+BART futures projection, representing the sum total of these regulations + mobile sources+heavy duty diesel+off-road regulations in 2020.

Accum Period:

Winter: Dec (previous year) - Feb Spring: March - May Summer: June - August Autumn: Sept - Nov

Atmospheric Modeling

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