Appendix 3-5

The National Atmospheric Deposition Program and Associated Monitoring Efforts

 

1           Introduction

 

            An objective of the Network design is to address atmospheric deposition of pollutants to establish their relationship to the conditions of inland and coastal water resources. Adequately determining deposition loadings to watersheds requires estimates on both the wet (e.g., rain, snow, fog, cloudwater, etcY) and dry (gaseous and particulate forms) components. Currently the primary network monitoring wet deposition is the National Atmospheric Deposition Program (NADP). 

 

            An increased number of stations monitoring wet deposition directly in estuarine areas would aid significantly in assessing direct deposition to coastal waters, including significant agricultural and urban areas in proximity to those waters. Better coverage of dry deposition sites can aid atmospheric deposition model verification. However, it should be recognized there is considerable variability in dry deposition of pollutants in coastal areas due to the complexities of estuarine land cover, and the presence of localized meteorological phenomena such as land/sea breezes. Thus, the increased number of stations along coastal areas may not proportionally increase the spatial resolution of dry deposition loading estimates.  But the increased number of stations would improve the models, which explain the spatial variabilities.  For this reason, the Network design proposes that new sites each be carefully considered.

 

            The NADP is a cooperative that includes federal and state agencies, universities, industry, Native American groups, and NGOs. It is a federation that requires participants to Abuy in@ to the program.  If a monitoring program can fund a site that meets certain criteria, then it can become part of the NADP. The NAPD has three subnetworks:  of the National Trends Network (NADP/NTN), the Atmospheric Integrated Research Monitoring Network (NADP/AIRMoN), and the Mercury Deposition Network (NADP/MDN). Station locations for these networks can be seen at http://nadp.sws.uiuc.edu/networks.html#adp.

 

            Data collected as a part of the NADP is collected weekly according to strict clean-handling procedures. It is then sent to the Central Analytical Laboratory where it is analyzed for hydrogen (acidity as pH), sulfate, nitrate, ammonium, chloride, and base cations (such as calcium, magnesium, potassium and sodium).

 

            The primary network estimating dry deposition loadings is the EPA=s Clean Air Status and Trends Network (CASTNet) program. An additional network, the Integrated Atmospheric Deposition Network (IADN), a program jointly run by Environment Canada and the U.S. EPA Great Lakes National Program Office, focuses on the deposition of toxic chemicals in the Great Lakes Region.  These networks are shown schematically in Figure 3- 5-1 below.

 

 

 

            These networks focus on atmospheric deposition of acids, nutrients, persistent bioaccumulative toxic (PBT) chemicals, and mercury, making them important to the monitoring of water resources.  Toxic chemical deposition now monitored  by the IADN, with current coverage limited to the Great Lakes, could also be extended to other areas, albeit at relatively high cost.  Currently there is little atmospheric monitoring information for PBTs outside of the Great Lakes, and extending IADN-like monitoring into other regions would help identify source areas and measure progress under domestic and international toxic reduction programs and agreements.  Costs for toxic chemical monitoring could possibly be reduced by centralizing analysis in government or contract laboratories.

 

            It should be noted that most of these stations are not well suited to establish source-receptor relationships since they involve relatively low temporal resolution (1 week). However, if a Ahot spot@ were identified, then an NADP/NTN site could be relatively easily upgraded to follow an NADP/AIRMoN protocol (daily sampling), allowing the source-receptor assessment for at least the wet deposition component.

 

            Because the NADP and CASTNet networks are well established, have widely-accepted protocols, and have relatively low costs, these networks are recommended as vehicles to expand atmospheric deposition monitoring to include more coastal areas.

            If the research need arises, and the additional manpower made available, an NADP/NTN site could be easily transformed to an NADP/AIRMoN site as a part of its research program.

 

1           Wet deposition of acids, nutrients and mercury

 

An NADP/NTN site provides weekly monitoring of:

Precipitation                      pH                   Conductivity

Concentrations of:

Ammonium                   CalciumChloride                       Hydrogen

Magnesium                   NitratePotassium                      Sodium

Sulfate

 

Deposition loadings are calculated through relating precipitation amounts and concentrations.  Increased utility of coastal stations can be obtained with the addition of monitoring for organic nitrogen, demonstrated to be a significant component of atmospherically deposited nitrogen.

 

An NADP/MDN site provides weekly sampling of precipitation amounts and concentrations of total mercury. Deposition loadings are also calculated through relating precipitation amounts and concentrations.

 

Currently, the NADP/NTN network consists of over 250 sites. However, relatively few are located in coastal areas.

 

There are over 85 sites in NADP/MDN, with around 10 at coastal sites. Figure 3-x, below shows their location in the conterminous United States. Two sites in Alaska are far from the coast.  Two sites are also active in Puerto Rico.

 

 

3. .  Dry deposition of acids and nutrients

 

A CASTNet site provides:

   weekly concentrations of nitric acid, nitrate, ammonium, sulfur dioxide, and sulfate

   hourly concentrations of ozone, and

   meteorological variables including temperature, humidity, wind speed, incoming solar radiation, and precipitation.

Adding monitoring for gaseous NH3 to coastal sites would enhance the value of this network sites to coastal water resource planning.

Dry deposition rates are calculated through an inferential method, using the Multi-Layer Resistance Model (MLM) to determine a deposition velocity, and combining this with concentrations to calculate a flux.

 

Because of the importance of measuring both dry and wet deposition CASTNet sites are collocated with NADP/NTN sites

 

There are 89 active CASTNET sites, with less than 10 at coastal sites.

 

CastNet sampling sites are shown in Figure 3-5-4.

 

 

 

4.   Wet and dry deposition of Persistent Bioaccumulative Toxic (PBT) pollutants

 

The IADN provides:

   Concentrations of PCBs, PAHs, and organochlorine pesticides in monthly composite precipitation samples

   Concentrations of the same analytes in the particle and gaseous phases from 24-hour air samples collected every 12 days

         Meteorological measurements including temperature, humidity, wind speed, solar radiation, and precipitation amounts

 

Dioxins and furans and polybrominated diphenyl ethers (PBDEs) are now being monitored by IADN on a temporary basis.  Given sufficient funding, this could be continued into the future.

 

There are 5 master stations in the network, one on each Great Lake.  Supplementing those stations are 10 satellite stations, including urban sites in Chicago and Cleveland.  Some of the satellite sites in Canada are precipitation-only.  Mercury is measured using automated Tekran mercury monitors at some Canadian sites.  Five of the 15 IADN stations are located in the United States and are operated by U.S. EPA-GLNPO.

 

IADN concentration data is used to calculate atmospheric loadings to the lakes and to examine trends in concentrations of these pollutants at the different stations over time.  Trends are also compared to those generated by GLNPO=s fish and water monitoring programs for PBTs.

 

 

5.  Increasing wet and dry deposition sites to address coastal water quality issues

 

To better meet the objectives of the MNM in coastal areas, it is necessary to increase the number of collocated NADP/NTN, NADP/MDN, and CASTNET monitoring stations along the coast.  PBT monitoring based on the IADN model should be added if possible.  The Network design proposes that this be done in two stages.

 

The first stage would involve installing stations at the mouths of coastal HUC 6 outflows to enable estimates of direct atmospheric deposition to coastal waters at the same locations that pollutant loading measurements are being performed. In some cases existing NADP/NTN coastal sites could be upgraded to include the other two instrument suites. In others it would involve establishing a new site as part of all three programs.

 

The second stage would add sites in areas slated for intensive estuary water quality studies. (See section 3.5.3.)

 

These sites would be implemented in increments to better quantify the significance of atmospheric sources directly to estuarine waters.  Incremental implementation would involve short-term studies (perhaps using mobile units) which would be extended with more permanent sampling equipment if the need for additional characterization is demonstrated. In the case of mercury deposition monitoring, for instance, this would involve finding fish contaminated by mercury and being unable to identify regulated sources responsible for emissions into water.  These sites would be implemented as candidate, and then as full members of the NADP.  This association will ensure that station siting and monitoring methods are consistent.