The requirement to monitor emissions on a regular and sometimes permanent basis has led to the development of a specific set of methods and techniques for the relevant industries.
Many of the air quality analyses can be performed with standard laboratory consumables, such as traditional filter papers. However, some analyses require materials with specific features, for example filters with low metal levels.
Common air monitoring applications include:
Airborne particulates are a composite group of substances (liquid or solid) dispersed in the atmosphere, ranging in diameter from a fraction of a micrometer to several hundred micrometers. Two of the most important fractions of particulate matter are the respirable fraction (< 2.5 μm) and the inhalable fraction (< 10 μm). The levels of these fractions are monitored by performing two specific gravimetric methods, PM2.5 and PM10 monitoring.
Glass fiber reel for automated samplers.
EPM 2000 glass fiber filters.
Many gravimetric methods for the determination of particulate matter in the atmosphere are based on collection onto a high-efficiency glass microfiber or quartz filter. This process involves the collection of airborne particulates by medium- or high-volume air sampling, typically over a period of eight hours or longer. The mass of particulate matter is determined by weighing the filter before and after sampling.
In the analysis of the particulate matter collected, care should be given to the choice of the filter medium used. The filter medium should give little or no background level for the elements and/or compounds being analyzed and cause minimal interference in the determination.
GE Healthcare's glass microfiber filters (such as GF/A and EPM2000) and quartz filters (such as QM-A) are particularly suitable for gravimetric determination of particulates due to the high retention efficiency of the media combined with rapid flow characteristics, low pressure drop, high loading capacity, and low affinity for moisture. PTFE membranes are often used for specific gravimetric analyses, e.g., PM2.5 monitoring or vehicle emissions testing, according to the employed methodology.
Stack gases are often monitored at high temperatures for which glass microfiber or quartz filters, such as QM-A or thimbles, are appropriate.
Quartz fiber filters.
Specific chemical components are monitored in order to measure the air quality.
The metal elements of major interest in air pollution monitoring include the heavy metals cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), manganese (Mn), zinc (Zn), cobalt (Co), and iron (Fe). A variety of techniques for the determination of other specific constituents are also routinely used. Care should be taken in choosing the optimum filter material for the particular application.
The emissions of major interest are smoke particulates, carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons, and nitrogen oxides. Gaseous emissions can be measured directly, using a glass microfiber filter such as GF/A or QMA to remove interfering particulates and oil mists.
Whatman EPM2000, QM-A, and ultrapure QM-H filters are often used in applications where reduced levels of Zn, Fe, and trace elements are required. In other routine chemical analysis cases, GF/A is a widely used filter.
Asbestos fibres on a cyclopore membrane
Asbestos was historically used as a construction material and fibers of this material can be found in many locations. As asbestos fibers can potentially cause cancer, it is important to monitor the general concentration of the fibers in the environment and not just in areas where buildings are being renovated or demolished. Areas with high population densities are subject to continuous testing regimes.
Asbestos analysis is commonly done with microscopy techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and phase contrast microscopy (PCOM). These methods usually involve sampling and/or observation using membrane filters such as polycarbonate or mixed cellulose ester membranes.
One common PCOM-based technique, known as the hot block method, employs a 0.8 μm cellulose membrane filter that is used to collect fibers from a defined volume of air.
Following collection of the sample, the membrane is made transparent using acetone vapor. Whilst many membranes initially give good transparency, only a few remain clear over time without the occurrence of crystalline artifacts that could present difficulties in subsequent analysis. This is an important aspect to consider when reviewing historical samples. GE Healthcare’s MembraClear mixed cellulose ester membranes were specifically introduced for this technique.
Glass microfiber filters combine fast flow rates with high loading capacity and very fine particle retention.
High-purity quartz microfiber filters for air sampling in aggressive environments (high temperature, acids).
Suitable for air sampling applications.
For aggressive solvents, liquids, and gases. Standard and custom formats.
Conforms to EPA PM 2.5 reference method under the requirements of 40 CFR part 50 Appendix L .
For highly specific applications such as cell capture, biosensors, erythrocyte deformability testing, or environmental testing.
Sterile and non-sterile membranes for filtration of aqueous solutions.
