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Evaluation of Optical Instruments for Real-Time Continuous Monitoring of Smoke Particulates
A comprehensive smoke management plan is essential for the successful use of fire as a wildland management tool. Monitoring ambient air to ensure that smoke does not threaten people or protected areas is an essential element of such a plan. The demands on a particle measurement device in a wildland fire situation are severe.
Ideally, the instrument should be portable (not require line power), be rugged, (it will be transported in remote areas), be easy to set up and operate by one person, retrieve data in useful forms, and have known accuracy even at low particulate concentrations where smoke would be just a nuisance.
The estimated mass concentrations from real-time instruments can be used for a variety of purposes. Real-time smoke concentration data can be used by the Forest Service to help manage a fire and its production of smoke. The data may also be used to anticipate public notification needs as well as to verify the smoke concentration that actually occurs for regulatory purposes. In the future, real-time smoke data may be used with smoke models to produce more accurate predictions of smoke concentrations.
Gravimetric or filter-based monitoring techniques have been used for years to quantify mass concentration levels of airborne particulate matter. Filter-based sampling is labor intensive. Filters must be conditioned, weighed before sampling, installed and removed from the instrument, and reconditioned and weighed again at special facilities. Results from the weighing may not be available for days or weeks, depending on the workload at the laboratory. Also, airflow rates and elapsed sampling time must be carefully monitored and recorded to ensure accurate results. Filter-based techniques integrate samples over a long period of time, usually 24 h (depending on the exposure), to obtain the required minimum mass for analysis. Filter-based techniques can have inaccuracies in both mass and composition due to the loss of volatile and semivolatile components. The components can be lost during collection or after collection but before the filter has been analyzed.
Optical, real-time, continuous particulate monitoring instruments do not have many of the problems associated with the gravimetric technique. Optical instruments do not require that filters be weighed. They provide concentration estimates that can be released immediately to land managers and the public. Many of these instruments are portable. They can be sited in the areas of greatest interest, usually downwind of burns.
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