Measurements of the 14C/12C ratio in environmental carbonaceous species can provide a unique indication of natural vs anthropogenic (fossil fuel) origin. Because of the low concentrations of atmospheric gases and particles which contain carbon, convenient sample sizes are limited to tens of milligrams of carbon. An assessment of the measurement feasibility, using 10 mg-C samples and Accelerator Mass Spectrometry and Low-Level Counting is given, together with the kinds of environmental problems which might be studied. Preliminary low-level gas-proportional counting results, are given for atmospheric particulate samples containing 5-10 mg-C.