Recently, there has been a keen demand for real-time automatic monitoring of VOCs not only in Korea but other
developed countries. We carried out this study to evaluate and to optimize the performance of a continuous automatic
monitoring system for hazardous VOCs (HVOCs) in the ambient atmosphere, using an on-line GC system. The online
system normally consisted of a Nafion dryer prior to a cold trap of an automatic thermal desorption apparatus
and a GC system equipped with two detectors, i.e. PID and ECD. Preliminary tests conducted to check out any contamination
of the system revealed an evidence of significant artifact formation of benzene, and it was found that the
Nafion dryer (even brand new one) is the source of the benzene artifact. Thus, all the subsequent experiments in this
study was carried out inevitably by removing the Nafion dryer.
The on-line GC method was investigated with a variety of QC/QA performance criteria such as repeatability, linearity,
lower detection limits, and accuracy. In order to find out the best operating condition for the on-line GC system,
three different types (in terms of adsorption strength) of cold trap combinations were tested, i.e. (i) Tenax-TA and
Carbopack-B combination (weak and hydrophobic); (ii) Tenax-TA, Carbopack-X and Carboxen-1000 combination
(strong and hydrophilic); and (iii) Tenax-TA and Carbopack-X combination (medium and hydrophobic/hydrophilic).
The USEPA TO-17 manual method was selected as a reference method to evaluate the performance of the on-line
method. A series of experiments revealed that the system performance was superior to others when a cold trap packed
with hydrophilic adsorbents (Tenax-TA/Carbopack-X/Carboxen-1000 combination) was used and operated at 25?C.
However, the system with a cold trap packed with a combination of Tenax-TA and Carbopack-X is more recommend-ed for field applications since the carboxen-1000 adsorbent is too sensitive to water vapor, and hence the performance
of the system might be very unstable to humid samples or during rainy days. Furthermore, the precision and accuracy
criteria of the Tenax-TA/ Carbopack-X combination were generally compatible with the triple adsorbents cold
trap. The continuous automatic monitoring method is, thus, considered very useful to real-time monitoring to understand
the variations of VOCs concentrations in ambient air, as it adopts much simpler procedures in sampling, analysis,
and data integration steps than manual monitoring methods. However, it should be noted that there is a high
possibility of benzene artifacts formation through the Nafion dryer, which is often installed to remove water vapor
in air samples before being adsorbed onto the cold trap. Therefore, if a Nafion dryer is used in any studies of monitoring
VOCs, the benzene contamination should be carefully examined before carrying out obtaining the data.