When carbon-14 signals approach background levels, the validity of assumptions concerning Poisson counting statistics and measurement system stability becomes crucial in interpreting the resultant low-level counting observations. This has been demonstrated in a previous study on detection limits for non-Poisson error, and it is critical in these current studies of carbonaceous pollutants, where the carbon-14 signal from just five milligrams of carbon is comparable to that of the background for the miniature gas proportional counters. To assure data quality, the multi-detector system is designed for the online monitoring of critical parameters that reflect both the statistical nature of the non-Poisson errors and the underlying physical causes. -- AATA