Simple Moving Average Applied to "ISO Method" CPAM Concentration Estimates: An Unexpected Result.

A surprisingly large amount of variance reduction has been observed when filtering International Organization for Standardization (ISO) "ISO Method" continuous particulate air monitor (CPAM) airborne radioactivity concentration estimates with a simple three-point moving average. This processing has relatively little lag relative to the amount of variance reduction obtained. The key factor producing this effect is the specific autocorrelation structure of the estimated concentrations, which are based on taking first differences of integrated-count data; this scheme results in successive count differences that contain a common count value between them.

Some Analysis of Integrated-count Processing for Fixed-filter Continuous Particulate Air Monitors.

A calculation for estimating concentrations of long-lived airborne particulate radioactivity using fixed-filter continuous air monitors is given in an ISO standard. The method uses counts integrated over relatively long time intervals, rather than the 'instantaneous' count rates that in digital systems are evaluated using much shorter time intervals and some form of variance-reduction filtering. This article presents three ways of deriving and interpreting this calculation, based on previously published mathematical models that were derived from first principles.

Incorrect interpretation of moving-filter continuous particulate air monitor responses.

The graphs supplied by the vendors of moving-filter continuous particulate air monitors (CPAMs) in their sales literature show linear curves on a log-log scale, with net count rate on one axis and concentration on the other. The implication is that the monitor user is to read the concentration from the graph, given an observed net count rate, at any time. For the nominal filter speeds commonly used for these monitors, using the graph in this way is incorrect.

Estimation of high-level, rapidly-changing concentrations using moving-filter continuous particulate air monitors.

A previously published mathematical model for the dynamic response of moving-filter continuous particulate air monitors has been enhanced to extend that model to include decay chains. During this work, it was observed that a quantitative relationship appeared to exist between the monitor count rate and the time-dependent particulate airborne radioactive material concentration if, and only if, the filter (tape) speed was much faster than the nominal 2.54 cm h(-1) (1 in h(-1)).

Degassing Lakes Nyos and Monoun: defusing certain disaster.

Since the catastrophic releases of CO(2) in the 1980s, Lakes Nyos and Monoun in Cameroon experienced CO(2) recharge at alarming rates of up to 80 mol/m(2) per yr. Total gas pressures reached 8.3 and 15.

Bias in concentration estimates due to nonconstant flow rate during particulate air sampling.

Correction for a nonconstant flow rate during particulate air sampling is often done by taking the arithmetic average of the initial and final flow rates. This average is then used in concentration calculations as if the flow rate had been constant at that value during the entire sampling period. For long-lived activity this approach is reasonable, but for shorter-lived activity and longer sampling times the estimated concentrations can be biased low.