Particulate test atmospheres, generation

When insufficient data are available, it may be necessary to generate test atmospheres to determine the physical state of a compound and the collection efficiency of a filter and vapor collector. The estimation of the vapor/particulate ratio may also depend on concentration and sample loading. For example, in a short sampling time, vapor may be efficiently collected on a filter, but longer term sampling may reveal saturation of the filter with vapor and eventual passage of the vapor into a backup bubbler or sorbent tube. 

If the ratio EVC/std is in the range 0.05 to 100-300, then a mixture of particulate and vapor may be present (7). A ratio above this range indicates the presence of vapor alone and below the range, particulate. The reliability of this determination depends on the accuracy of vapor pressure data. In method development and validation studies, it is often necessary to perform special tests with generated test atmospheres at different temperatures and concentrations to demonstrate the physical form of the substance. 

Laskin-Type Nozzle Generator. A third type of atomizer, the Laskin-type nozzle generator, is used to create test atmospheres of particulate or aerosol and vapor mixtures. A pure liquid or melt is used, and no solvent is necessary. Again, this is important for evaluating filter and solid sorbent combination sampling trains. 

Figure 8. Glass generator for particulate/vapor test atmospheres...

When low dispersible material is subjected to the high velocity impact test, particulate matter can be generated, but of aU airborne particulates up to 100 pm only a small (less than 10%) fraction will be expected to be in the respirable size range below 10 pm if the 100 limit is met. In other words, an equivalent quantity of low dispersible material less than 10 A2 could be released airborne in a respirable size range. It has been shown that for a reference distance of around 100 m and for a large fraction of atmospheric dispersion conditions this would lead to an effective dose below 50 mSv. 

---