PM/Gas Sampling Cartridges...
The ChemComb Speciation Sampling Cartridge is a flexible, field-proven module for the sampling of atmospheric gases and particles. It can be configured for single- or multi-stage sampling of PM-2.5 or PM-10. The cartridge can be outfitted with honeycomb denuders for the stripping and/or sampling of selected gases.
The sampling device is made up of a single cartridge that contains a well-characterized inlet with a PM-2.5 or PM-10 impactor, up to two honeycomb denuders for the removal or collection of selected gases, and a four-stage 47 mm diameter filter pack for the collection of particle-related components. PM-2.5 inlets are available for flow rates of 10 and 16.7 l/min, and the PM-10 inlet operates at a 10 l/min flow rate. The honeycomb denuders achieve their high collection efficiency at the 10 l/min flow rate. Systems can also be configured without honeycomb denuders to operate as a multistage filter pack for PM-2.5 or PM-10.
All sampling components are assembled in the laboratory and enclosed in the sampler's container. This eliminates the risks inherent with in-field assembly of sampling components. A small, rugged form factor permits easy transport or shipment of ChemComb cartridges in its assembled form between the laboratory and the air sampling site.
ChemComb cartridges can be used in a variety of sampling systems, ranging from Thermo's Partisol Model 2300 Speciation Sampler, Mini-Partisol Model 2100 Air Sampler and original Partisol Model 2000 Air Sampler, to simple configurations involving a flow-regulated pump.
The sample inlet is designed to reduce the sample stream's residence time and contact with surfaces. A PTFE coating used in many applications minimizes losses of HNO3 and NH3. Clear anodized inlets are available for the collection of organic and elemental carbon on quartz fiber filters to avoid possible interferences from inlet surface coatings.
The system achieves its sharp PM-2.5 or PM-10 size selection by means of impaction onto a greased impactor well, resulting in a cut points characteristics similar to those used in USEPA reference-designated samplers. Analyses by the Harvard School of Public Heath show the cut point performance for the 10 l/min PM-2.5 inlet, the 16.7 l/min PM-2.5 inlet, and the 10 l/min PM-10 inlet.
Honeycomb denuders are small, rugged, and contain a large internal surface area. They are 47 mm in diameter, and only 38 mm long. Their internal surface area of 508 cm² is made possible by 212 hexagonal flow channels that are 2 mm on a side. This results in a much higher loading capability than conventional 200 mm long annular denuders, which typically have an internal surface area of approximately 310 cm². The entire ChemComb cartridge is less than 30 cm long.
Honeycomb denuders are made completely of glass to avoid gas losses that can take place due to nitric acid and ammonia adsorption on the epoxy resin sometimes used in annular denuders. The use of the same material throughout the denuder avoids cracking that can otherwise occur due to large temperature changes.
Honeycomb denuders are efficient collectors of inorganic gases such as HONO, HNO3 and NH3 through the application of different coatings in the laboratory. A denuder may be coated with a different gas-adsorbing substance each time it is used.
Typically, a sodium carbonate/glycerol coating is used for the collection of acidic gases such as SO2, HONO and HNO3. A second denuder in series is often coated with a citric acid/glycerol solution for the collection of basic gases such as NH3. Ion chromatography is often used as the analytical method.
The four-stage 47 mm diameter filter pack is made of Teflon material to avoid interferences. It is not necessary to populate each stage of the filter holder with a collection filter. An intensive application of the ChemComb cartridge involves the following three 47 mm diameter filters: 1) a 2 µm pore-size Teflon filter for the collection of fine PM; 2) a glass fiber filter coated with sodium carbonate (Na2CO3) for the collection of nitric acid (HNO3); and 3) a glass fiber filter coated with citric acid for the collection of ammonia (NH3).
Testing of PM-2.5 ChemComb Cartridges performed by the Harvard School of Public Health show that particulate mass, sulfate and nitrate through a 10 l/min inlet and particulate mass, sulfate and nitrate through a 16.7 l/min inlet compare closely with values obtained from a USEPA PM-2.5 reference-designated air sampler.
Thermo is currently taking steps in conjunction with a number of institutions to develop new configurations of the ChemComb. One of the first will be a flexible design for the sampling of organic materials and gases contained in ambient air.
0 Items 
