ACCESS NUMBER: 30720

STUDY TITLE: Effects of Offshore Emissions on Ambient Levels of Atmospheric SO2 

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REPORT TITLE: Measurements of SO2 Concentration And Atmospheric Structure In 

Delta And Breton Wildlife Refuges, Louisiana In The Summer, 1993 

CONTRACT NUMBER: 14-35-0001-30720 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA: Northeastern 

FISCAL YEAR(S) OF PROJECT FUNDING: 1993 

COMPLETION DATE OF REPORT: March 1995 

COST: FY 1993: $59,664 

CUMULATIVE PROJECT COST: $59,664 

PROGRAM MANAGER: S. A. Hsu 

AFFILIATION: Coastal Studies Institute 

ADDRESS: Howe-Russell Geoscience Bldg., Louisiana State University, Baton Rouge, 

Louisiana, 70803 

PRINCIPAL INVESTIGATOR: S. A. Hsu 

KEY WORDS: Northeast Gulf of Mexico; Delta Wildlife Refuge; Breton Wildlife Refuge; 

air pollution; ambient SO2; energy production; radiosondes; mixing height; NAAQS; 

Class I; Class II. 

BACKGROUND: Considerable offshore energy production is in existence in the Outer 

Continental Shelf (OCS) region of the Gulf of Mexico. Portions of the coastlines of 

Louisiana, Mississippi, and Alabama and their associated barrier islands serve as 

National Seashores and Wildlife Refuges, and have been designated as Class I and II 

by the EPA. Since emissions of sulphur compounds and nitrous oxides are a byproduct of the OCS production, it seems inevitable that some of these pollutants will 

affect these protected areas. This report presents the results of a pilot study to 

determine the current ambient concentration of SO2 in these areas as well as some 

aspects of the local meteorology which may influence pollution transport. 

OBJECTIVES: (1) Measurements of atmospheric SO2 concentrations and local 

meteorological conditions in the Breton and Delta Wildlife Refuges; and (2) analysis of 

the structure of the marine atmosphere over these areas. 
ACCESS NUMBER: 30720

DESCRIPTION: During the summer months, high pressure systems typically prevail 

over the northeast Gulf of Mexico, creating air stagnation and the likelihood of high 

ambient pollution concentrations. Three stations were established during July - 

September 1993 to monitor atmospheric SO2 concentrations and meteorological 

conditions: two in the Class I Breton Wildlife Refuge at Gosier Island (29°29.34'N 

89°10.45'W), and the third in the Delta Wildlife Refuge at Pass-A-Loutre. SO2

concentration was measured at all sites by a Thermo-Electron Model 43A Pulsed 

Fluorescence SO2 Analyzer. Measured meteorological parameters included surface air 

temperature and wind speed and direction. Data was recorded on site by dataloggers 

which were downloaded several times during the deployment when the stations were 

serviced and calibrated. 

SIGNIFICANT CONCLUSIONS: Maximum 24 hour average SO2 concentration (3 ppb) 

measured during the study period was only 2% of the NAAQS (140 ppb) allowable once 

per year. Average SO2 concentrations appear higher in the Breton Wildlife Refuge than 

at the Delta Wildlife Refuge. Large scale weather events (fronts, low pressure centers, 

tropical storms, etc.) appear to directly affect pollution concentrations in our study area. 

Average mixing heights over the area were approximately 670 m. 

STUDY RESULTS: Harsh environmental conditions and the necessary use of battery 

power caused much of the air quality records from Breton and Gosier Islands to be 

excluded from this analysis. Good instrument calibrations were achieved during the 

final three weeks of the deployment at all sites. Comparison of the meteorological data 

records shows excellent agreement amongst the sites, which suggests that weather 

conditions were nearly homogeneous over the area. During these weeks, an early 

season frontal passage occurred on 11 September 1993. Averaged 3-hour and 24-hour 

SO2 concentrations at each site were at least twice as high after the frontal passage 

(when wind blew from land to sea) as pre-frontal (from sea to land), with concentrations 

at the Breton Wildlife Refuge 2 to 3 time higher than at the Delta Wildlife Refuge. 

However, it should be noted that the majority of all hourly concentrations recorded after 

calibration was less than 10 ppb. 

As part of a separate air quality study conducted during the summer of 1993 (Gulf of 

Mexico Air Quality Study), radiosondes were launched a minimum of twice daily from 

the Chevron platform GB 236A (located at 27.8°N 93.1°W). This data set was analyzed 

to determine the mixing height to be about 670 m over GB 236A. Since there is little 

variation in air and sea surface temperatures over the shelf in the summer, these height 

statistics should approximate conditions over our area as well. 

STUDY PRODUCT(S): Hsu, S.A. 1995. Measurement of SO2 concentration and 

atmospheric structure in Delta and Breton Wildlife Refuges, Louisiana in the summer 

1993. U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS 

Region, New Orleans, LA. OCS Study MMS 95-0019. 74 pp.