image: EPA 454-R-04-002, Fig 2
What procedure is best to determine background airborne silica levels?
A major community question has been, "what percentage of airborne PM is from the mines or dangerous crystalline silica?
Both industry and community-collected PM measurements would benefit from a better understanding of the relative mixture of silica and other PM sources in background air quality.
24-hour samples with the MiniVol can be subjected to several different lab methods to determine silica content of PM. Three different lab methods are available for the Minivol that can look at silica content. These are the same cost regardless of whether PM2.5, PM10, or PM4 are measured:
|Analysis Method||Analysis target||cost||notes|
|Gravimetric analysis, NIOSH 0500||Total mass of PM||$20-25||essential first step before other tests|
|X-Ray Fluorescence (XRF)||total silicon||$30||elemental silicon, not silica or crystalline silica specifically|
|X-Ray Spectroscopy (XRD)||Quartz only||$65|
|X-Ray Spectroscopy (XRD)||Quartz & Cristobalite||$75|
|X-Ray Spectroscopy (XRD) NIOSH 7500||Cristobalite and Tridymite||$85|
How many 24-hour sampling periods are needed to say something meaningful about background silica levels?
This question can be divided into two questions, I believe.
- what meets Federal Reference Method requirements?
- what is statistically significant?