The Reston Groundwater Dating Laboratory

Estimating CFC Air Curves

When atmospheric measurements are not available (early end of CFC dating ranges), estimates of production and release must be made using information from the Chemical Manufacturers Association (CMA) and the Alternate Fluorocarbon Environmental Acceptability Study (AFEAS).

The quality of production data is deteriorating due to unreported data and under-reporting. Calculations indicate significant under-reporting after the Montreal Protocol.

The release of CFCs into the atmosphere must account for the following:


Dating capabilities for CFCs

95% of the CFCs are released in the northern hemisphere with interhemispheric exchange occurring within 1.1-1.4 years. Seasonal variations also occur, with the highest concentrations in the spring.

CFC concentrations are higher over cities and urban areas. When sampling in urban or industrial areas, local atmospheric measurements may be more useful for CFC reconstructions than global atmospheric CFC measurements that do not account for the local anomalies.