Whatman high purity quartz (SiO2) microfibre filters are used for air sampling in acidic gases, stacks, flues and aerosols, particularly at high temperatures up to 500°C and in PM-10 testing. Because of the low level of alkaline earth metals, "artifact" products of sulfates and nitrates (from SO2 and NO2) are virtually eliminated. QM-A, sequentially numbered according to EPA standards, is suitable for most applications. Diameter: 9.0cm. 100/Pack. Whatman #: 1851-090.