Emission sampling trains are grab sample equipment, essentially consisting of a probe, a series of impingers, a gas meter, and a pump. Presently, more than thirty variations of sampling trains are used on different pollutants and/or applications. These variations may simply be using different absorbing chemicals or number of impingers, but may also include modifications to the system or addition of accessories. In this section, a few representative methods used in sampling some commonly tested pollutants are described.
Total Particulate Determination (RM 5 or RM 17) - Emission Parameter Analyzers that conform to EPA Reference Method 5 (RM 5, Determination of Particulate Emissions from Stationary Sources) design specifications are used to obtain the velocity profile, moisture content, and particulate samples. Dry particulate is collected isokinetically on glass fiber filters that are rated 99.95% efficient in collecting particles larger than 0.3 microns. Condensable particulate (less than 0.3 microns) and flue gas moisture volumes are collected in a train of four Greenburg-Smith impingers submerged in an ice water bath. The particulate loading is determined gravimetrically by accurately weighing the desiccated filter and probe-nozzle wash boil-off residue per the EPA procedures.
SO2/SO3/H2SO4 Determination (RM 8 or TCEQ Combined Method) - To measure the SO2/SO3/H2SO4 concentrations, a modified Reference Method 5 train replacing DI water with chemicals is used. In this method, sample gas is drawn from the stack or duct and passes through a probe with borosilicate or quartz liner to a series of impingers filled with chemicals. Glass fiber or quartz filters are placed between the probe liner and the impingers. The filter can be placed before the first impinger or between the first and second impingers depending on the method and the corresponding sampling procedures. The probe and filter are heated above the acid dew point to prevent acid condensation. Particulate sulfur and acid mist are collected on the filters while gaseous sulfur compounds are collected in a series of impingers. Typically, the first impinger contains a mixture of DI water with isopropyl alcohol while the second and third impingers contain 3 to 6% hydrogen peroxide (H2O2) solutions to convert the SO3 and SO2 in the gas to H2SO4. Similar to the RM 5 train, all impingers are submerged in an ice bath to condense the flue gas moisture and maintain an optimum collection efficiency. Sample flow rates are measured by a dry gas meter connected downstream of the impingers. In most cases the sample rates are kept at isokinetic. After completion of the test run, all glassware is rinsed with DI water and the rinses, along with impinger solutions, are titrated with barium perchlorate (Ba(ClO4)2) solution to determine the H2SO4 concentrations. The SO2, SO3, and H2SO4 speciations are determined by the trapping media, i.e., sulfates (SO42-) are collected on the filters, sulfur trioxide (SO3) is collected in the first impinger, while sulfur dioxide (SO2) is collected in the peroxide solutions. One or all of the sulfur species may be determined in the same test.
Chloride/Chlorine (HCl/Cl2) Determination (RM 26) - Chloride/chlorine conentration in a gas stream is determined using a modified RM 5 train. Instead of the standard four impingers, six impingers are used. Samples are usually collected isokinetically while solutions are analyzed using ion chromatography (IC) to determine the chloride/chlorine concentrations.
Particulate Matter Less Than or Equal to Ten Microns (PM10) (RM 201A) - A modified RM 5 train with a 10-micron cyclone attached to the front of the probe is used to measure particulate matter less than or equal to ten microns. The cyclone is designed such that when the sample is collected isokinetically under proper dwell time, particles larger than 10 microns are retained in the cyclone, allowing only particles smaller than or equal to 10 microns to pass through and deposit on a quartz or fiberglass filter. The filter and probe-wash boil-off gains are determined gravimetrically. Determination of total particulate loading is possible with this method; however, the results are usually biased high.
Multi-Metals Determination (RM 29 or Method 0012) - A modified Reference Method 5 train is used to trap metals. Flue gas samples are drawn isokinetically through a series of seven impingers containing dilute nitric acid and permanganate/sulfuric acid solutions to collect condensable particulate matter and volatile metals. All metals except mercury are analyzed using atomic absorption spectroscopy (AAS) or inductively coupled argon plasma emission spectroscopy (ICAP). Mercury is analyzed using cold vapor atomic absorption spectroscopy (CVAAS).