Emission Measurement using Dynamic Flux Chamber Method (2008-2009)

Accurate emission measurement is critical to assessing and developing effective emission reduction strategies. Flux chamber method directly measures emissions from the ground. There are two types of flux chambers: static (closed, passive) and dynamic (flow-through, active). The static chamber provides instantaneous flux estimates as measurement is made within a short period of time (e.g., minutes) upon chamber placement; but the measurements are often intermittent and sampling is laborious.  In contrast, the dynamic flux chamber (DFC) can provide continuous sampling once installed in the field; thus is more accurate in estimating cumulative or total emission loss. Based on literature, a DFC system was developed to meet the emission monitoring needs for several PAW projects.

The DFC system consists of two major components: a flow-through chamber, and an automated sampling control and data recording module (electronic box). When steady state air flow is established within the chamber, emitted fumigants such as 1,3-D and chloropicrin are captured on XAD-4 resin in sampling tubes at the outlet of the chamber.  The sampling tubes are later extracted and analyzed for the fumigant using a GC-µECD system in the laboratory. The sampling frequency is greater for the first few days (2-4 h intervals) following fumigant application when emissions are high and reduced later (6 h) when emission rates are lower. The average flux (f) during the sampling period of time is calculated:                                                                                                             

Where Q is the total air flow through the chamber, q_s is the sample flow and m is the total fumigant mass captured on the sampling tube (s) during the sampling time interval (?t). Major obstacles during the chamber development included water condensation when temperature drops in the evening below the dew point that caused malfunction of flow meters. This problem was resolved by adding a heating unit to  the air entering the electronic box.  More details about the chambers can be found in the publication below.

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Relevant Publications include:

• Book chapter. Gao and Wang, 2011.
• MBAO 2008 presentation; proceedings
• MBAO 2009 presentation; Proceedings. XAD Resin for traping of gaseous fumigants (Gao et al., 2011).