Chesapeake Bay Atmospheric Deposition Study

Program Description

The Chesapeake Bay Atmospheric Deposition Study (CBADS) was conducted at three non-urban sites along the shoreline of the Bay during 1990-1993. The primary objective of the CBADS study was to provide the best possible estimates of total, annual atmospheric loadings of a variety of trace elements and organic contaminants directly to the surface waters of the Chesapeake Bay. To that end, ambient atmospheric concentrations of selected organic contaminants (gas and aerosol phases) and trace elements (aerosols) were measured. Also, wet depositional fluxes of target organic contaminants and trace elements were measured through the collection and analysis of precipitation samples. Precipitation and ambient air measurements were then used in deposition models to estimate the annual atmospheric wet and dry deposition loadings of target species to the surface waters of the Chesapeake Bay. This study was sponsored by the Maryland Department of Natural Resources, Power Plant Research Program (PPRP) and the U.S. Environmental Protection Agency (EPA).

The northern-most monitoring site was located at the University of Maryland’s Wye Agricultural Research and Experimental Station (latitude 38°53' north and longitude 76°08' west) on the shore of the Wye River, in Queen Anne’s County, Maryland. The mid-Bay site was located in a wooded area on the western shore of the Bay between the mouths of the Patuxent and Potomac Rivers (latitude 38°13' north and longitude 76°23' west), in St. Mary’s County, Maryland. The southern-most site was located at Haven Beach (latitude 37°26' north and longitude 76°15' west) in Mathews County, Virginia, approximately 100 km due east of Richmond, Virginia.

Initially, air samples for trace element analysis were collected at seven day (168 hour) intervals. Beginning in 1992, air samples for trace element analysis were collected over a 12 hour period once every seven days. For the organic contaminants, air sampling times ranged from 12 to 24 hours, depending upon the season. Ambient air samples were collected bi-weekly (i.e., every other Tuesday) to correspond with the precipitation sampling schedule. Meteorological data (wind speed, wind direction, air temperature, relative humidity, and rainfall) also were recorded.

Sampling was initiated at the mid-Bay site in Summer, 1990, with the northern and southern stations beginning operation later in 1990 and in early 1991, respectively. Sampling continued through September 1993. During the summer of 1993, an intensive sampling program, consisting of event-based precipitation sampling and daily air sampling for 28 days, was conducted in order to study sources of atmospheric pollutants and to better understand scavenging by precipitation.

See the Related Publications section below for sources of information on the CBADS monitoring program.

Precipitation/Air Sampling and Analysis

Precipitation samples from Aerochem Metrics Model 301 automated wet-only collectors were analyzed for trace metals, major ions, and organic contaminants. Trace element concentration quantification involved analysis of weekly integrated precipitation samples from a wet-only collector which was specially modified for trace element work. The trace elements included aluminum, inorganic arsenic, cadmium, nickel, selenium, zinc, copper, iron, manganese, and lead. Concentrations of major ions in weekly precipitation samples were determined by separate sampling at each site, either as part of the NAPAP (Wye), the Maryland STAR network (Elms), or as part of this study (Haven). The major ions included Cl^-, NO₃^-, SO₄^-2, Ca⁺², Mg⁺², K⁺, Na⁺, as well as pH. Organic contaminants concentration quantification involved analysis of precipitation samples from a wet-only collector modified for in situ isolation of organic compounds. Sampling for organic contaminants in precipitation (and in the vapor and aerosol phases) was integrated over two week intervals. The organic contaminants included selective polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl congeners (PCBs), and organochlorine agrochemicals. Precipitation intensities and amounts were measured using Belfort gauges or, when not available, estimated from the volume of precipitation collected for chemical analyses.

High volume air samples were collected using glass fiber filters to collect aerosols (trace elements and organic contaminants) followed by polyurethane foam plugs in series to trap vapors (organic contaminants). Each filter was analyzed for up to 40 trace elements, including aluminum, arsenic, chromium, cadmium, sulfur, selenium, zinc, nickel, lead, and copper. The filter and foam plugs were analyzed for 14 target PAHs, 75 PCB congeners , and various organochlorine agrochemicals.

Quality Assurance (QA)

The project goal was to generate data that were precise to within ±20% and accurate to within 20% of the true values. In addition, the sampling program was designed to reliably capture >90% of all samples.

To those ends, a formal QA plan was developed for the CBADS and submitted to the Chesapeake Bay Program Office of EPA. The plan outlined sampling procedures, field calibration procedures, sample custody, laboratory analysis procedures, laboratory calibration procedures, and QA checks and auditing procedures. The plan also outlined the responsibilities of each principal investigator regarding QA audits, preventative maintenance, corrective action procedures, data reduction, and report preparation. The plan provided a series of Standard Operating Procedure documents for field sampling; cleaning glassware (for organic contaminants analysis); preparing organic contaminant collection media; extracting, concentrating, and purifying organic contaminants; identifying and quantifying chlorinated compounds; and identifying and quantifying aromatic hydrocarbons. QA results, including estimates of precision and accuracy, as well as system audit reviews, were reported to the EPA Chesapeake Bay Liaison Office.

Related Publications/Reports

• Leister, D.L. and J.E. Baker. 1994. Atmospheric deposition of organic contaminants to the Chesapeake Bay. Atmos. Environ., 28, 1499-1520.
• Poster, D.L., R.M. Hoff, and J.E. Baker. 1995. Measurement of particle size distributions of semivolatile organic contaminants in the atmosphere. Environ. Sci. Technol., 29, 1990-1997.
• Poster, D.L. and J.E. Baker. 1995. Mechanisms of wet deposition of organic contaminants. In: Atmospheric Deposition of Contaminants to the Great Lakes and Coastal Waters, ed. by J.E. Baker,
• Society of Environmental Toxicology and Chemistry Special Publication Series.
• Poster, D.L. and J.E. Baker. 1996. Influence of submicron particles on hydrophobic organic contaminants in precipitation. 1. Concentrations and distributions of organic contaminants in rainwater. Environ. Sci. Technol., 30.
• Poster, D.L. and J.E. Baker. 1996. Influence of submicron particles on hydrophobic organic contaminants in precipitation. 2. Scavenging of polycyclic aromatic hydrocarbons by precipitation. Environ. Sci. Technol., 30.
• Scudlark, J.R., T.M. Church, and K.M. Conko. 1992. A method for the automated collection, proper handling and accurate analysis of trace metals in precipitation. In: The Deposition and Fate of Trace Metals in Our Environment, ed. by E.S. Verry and S.J. Vermette, Proceedings of the NADP Symposium, 8 October 1991, U.S. Forest Service Report No. NC-150, 57-71.
• Scudlark, J.R., K.M. Conko, and T.M. Church. 1994. Atmospheric wet deposition of trace elements to the Chesapeake Bay: CBAD year 1 results. Atmos. Environ., 28, 1487-1498.
• Wu, Z.Y., H. Han, Z.C. Lin, and J.M. Ondov. 1994. Chesapeake Bay Atmospheric Deposition Study, Year 1: Sources and dry deposition of selected elements in aerosol particles. Atmos. Environ., 28, 1471-1486.

The following Chesapeake Bay Program reports on the CBADS are available from the Maryland PPRP:

• Chesapeake Bay Atmospheric Deposition Study Final Report, Prepared by J.E. Baker and C.A. Clark for the Chesapeake Bay Program, August 1996, EPA 903-R-96-005, CBP/TRS 146/96.
• Chesapeake Bay Atmospheric Deposition Study, Phase I: July 1990 - June 1991, Appendices, Chesapeake Bay Program, March 1994, CBP/TRS 105/94. (This report includes the CBADS Quality Assurance Plan.)
• Chesapeake Bay Atmospheric Deposition Study, Phase II: July 1990 - December 1991, Appendices, Chesapeake Bay Program, July 1994, CBP/TRS 119/94.
• Expansion of the Chesapeake Bay atmospheric deposition network to create an integrated nutrient-toxics deposition monitoring program. Final Report submitted to United States Environmental Protection Agency, Baker, J.E. 2000. Ref. No. 00-0199-CBL. [UMCES Technical Series No. TS-271-00-CBL].

Go to the Chesapeake Bay Atmospheric Deposition Study Data Page

For more information, e-mail Dr. John Sherwell at the PPRP, or call him at 410-260-8660.