Air quality monitoring is ever evolving, responding to changing standards and situations. Pure quartz filters provide the thermal stability and low heavy metal content necessary for sampling in harsh environments, such as industrial stacks and flues.
The changing needs of air particulate testing
Accurate and reliable air monitoring is an essential part of the global effort of tackling pollution. Academic researchers, government and independent labs, power and utility companies, and industrial manufacturers all have roles in assessing emissions and their effects on human health and the environment.
As regulations evolve, industries must adapt to improve efficiency and reduce stationary emissions. The gravimetric determination of airborne particulates, such as PM2.5, PM10, organic and elemental carbon, and heavy metals, is a key part of this effort. Testing must be accurate and reliable to assess and guide improvements.
Accurate analyses rely on having appropriate sampling methods and materials, namely glass fiber and quartz filters, designed to support reliable sampling in a variety of environments.
Download the Whatman air particulate sampling product guide
Filters used in air monitoring
Glass fiber for remote monitoring
What makes glass fiber (borosilicate glass) well-suited for remote air monitoring applications? The material offers:
- High retention efficiency
- Excellent strength
- Good temperature resistance
Continuous air monitoring devices use glass fiber tape, such as Whatman grades GF10 and HGF61, to capture particulate matter across a range of complex conditions, including fluctuating temperatures and humidity.
Indeed, part of China’s success in improving air quality has been down to a nationwide network of continuous air monitoring devices that rely on glass fiber tape to capture and assess levels of PM2.5.
Quartz filters for harsh environments
Sampling air from stacks, flues, and other stationary emission sources requires a filter material that can withstand high temperature, high humidity, and acidic gases such as SO2 and NO2.
Over long sampling periods under these conditions, compounds and any trace contaminants in glass fiber filters can react with the acids to form artifacts that affect the accuracy of gravimetric determination and chemical element analysis.
An alternative to glass fiber comes in the form of quartz filters, consisting of high purity silicon dioxide (SiO2). These filters are well suited for use in harsh acidic environments as they have a different chemical profile to glass fiber, reducing the risk of artifact formation, and do not require binders. Whatman QM-A high purity quartz filters have been used for air sampling for many years, and the demands on the material are greater than ever.
The stringent manufacturing and quality control process used for quartz filters results in:
- High thermal stability
- Negligible amounts of heavy metal contaminants
- Suitability for heavy metal and other chemical analyses when borosilicate glass is not sufficient
- Virtual elimination of artifact formation
These properties, particularly the purity and temperature resistance, make quartz filters suited for the harsh air sampling conditions involved in organic and elemental carbon monitoring, and the extended sampling periods (>8 hours) required for heavy metal testing.
Whatman quartz filters: pure, but not simple
For many years, academic researchers, government and independent labs, and industrial scientists have used Whatman QM-A high purity filters for air monitoring. These established filters combine several properties that make them excellent air particulate sampling filters:
- High retention efficiency (99.9%)
- High purity
- Rapid flow characteristics
- Low pressure drop
- High loading capacity
- Low affinity for moisture
The demands on quartz have grown due to increasingly stringent standards and a push to continually improve efficiency and emissions. In response, Whatman has expanded its range of quartz filters, with the recent addition of QM-C.
Whatman QM-C is a 100% pure quartz fiber filter with extremely low heavy metal content resulting from stringent control during manufacturing and final QC process. The QM-C filters enable an extremely high level of sensitivity and accuracy, and provide thermal stability up to 1200°C. QM-C filters are, therefore, well suited for the most demanding applications for high temperature air sampling high sensitivity.
Table 1 shows the typical properties of the Whatman range of air monitoring filters.
Table 1: Comparison of properties of Whatman air monitoring filters, including QM-C pure quartz filters
| Grade | Typical air retention efficiency @0.3 µm | Thickness (µm) | Nominal basis weight (g/m2) | Temperature resistance | Binder | Pre-fired |
|---|---|---|---|---|---|---|
| GF/A | 99.9% | 260 | 53 | 550 °C | No | No |
| EPM2000 | 99.9% |
450 | 85 | 550 °C | No |
Yes |
| QM-A | 99.9% |
475 | 85 | 800 °C | No |
Yes |
| QM-B | 99.9% |
950 | 170 | 800 °C | No |
Yes |
| QM-C | 99.9% |
475 | 85 | 1200 °C | No |
Yes |
| QM-H | 99.9% |
430 | 85 | 900 °C | No |
No |
| GF10 | 99.9% |
350 | 70 | 180 °C | Yes | No |
| HGF61 | 99.9% |
285 | 54 | 180 °C | Yes |
No |
Supporting the evolving climate of air monitoring
Whatman’s global team of filtration specialists continues to support customers as their needs change and businesses evolve to meet new challenges. The introduction of QM-C quartz filters is a part of this forward-thinking effort, expanding the already comprehensive range of air monitoring filters available.
While QM-A continues to be the most appropriate and cost-effective choice for most situations, customers who require extremely high thermal resistance or purity in their quartz filters can benefit from Whatman QM-C filters.
For more information on air particulate sampling or to discuss your specific needs, speak with your local Cytiva representative or contact the Scientific Support team.