Page 476 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

15.2 Source Sampling 457

Fig. 15.11 Equal area
method for a rectangular duct

Equal area method is also applicable to rectangular duct, where the determina-
tion of the sampling points is much simple. The duct perimeter is first divided into a
number of girds and the sampling points are chosen at the center of each grid
(Fig. 15.11). The more sampling points the more representative samples can be
obtained. However, one has to compromise for time and costs.

15.3 Collection of Air Pollutant Samples

After sampled stack gas is extracted from the bulk air stream into the probe nozzle,
this air sample is further drawn through a sampling train or a series of leak-proof
equipment components configured to capture different air pollutants of concern. As
seen in Fig. 15.2 (Method 5), water vapor and condensable are best captured by
condensation or bubbling the sample gas through chilled impingers, which are
sealed glass vessels. Liquid reagents may be added into the impingers to absorb
some gases. Solids are likely captured on heated filters, which are connected to the
probe with interconnecting glassware. Solids can also be captured by liquids in
impingers.
The mass of the target air pollutant separated from the sample gas can be deter-
mined by the weights before and after sampling. Filters are weighed and reagent
volumes in the impingers are measured prior to use. After each run, the content of
each sampling train component is carefully recovered to a sealed vessel followed by
weighing the solid loaded filters or liquids from the impingers. For some tests, the
samples collected may be evaluated in a laboratory using scientific equipment.

15.4 Data Analysis and Reporting

Regardless of the end use of the data, the immediate objective of source tests is to
obtain reliable and representative information of the air emissions and the rates of
emissions into the atmosphere.