SEA's FTIR Results: Feb.'98

North Fenceline

 

Results of SEA's post-analysis of raw FTIR data supplied by Tosco Oil Co.

 Target Compound

 # Hits confirmed

 Max conc.

 Avg. conc.

 Min. detect

 Avg. MDL*

 Min. MDL

 Max. MDL

 # false positive

 MTBE

 63

0.242

0.076

0.032 

 0.044

 0.019

 0.322

 0
 2-methyl pentane

 7

 0.346

 0.231

 0.139

 0.149

 0.054

 1.035

 0
 3-methyl pentane

 44

 0.274

 0.111

 0.059

 0.125

 0.030

 1.531

 0
 n-heptane

 0
     

 0.068

 0.016

 0.803

 0
 propane

 0
     

 0.288

 0.061

 4.628

carbonyl sulfide

 0
     

 0.054

 0.025

 0.294

 methane

 54

 0.305

 -0.085

 -1.966**

 1.013

0.076 
 12.609

 0

All gas concentrations reported in parts-per-million (ppm)

 

*"MDL" stands for Minimum Detection Limit.

New MDL's are calculated for each target compound with the logging of each data point. By tracking these figures, the FTIR operator can gauge instrument performance at any given time. The figures also provide an easy point of reference when comparing our results with those arrived at by the refinery's contractors in real-time.

You may notice that the detection limits, or MDLs, for some of the chemicals reported above are significantly better (lower) than those reported by the refinery for the same time period see Feb FTIR data. For other chemicals, the refinery's detection limits appear to be slightly better than what we have been able to achieve. This would tend to indicate that the specific FTIR analytical programs (script files) being employed by both Terra Air Services and by us at SEA still have room for improvement.

 

**About the Methane Figures

In our analytical routines, we are not subtracting methane (or any of the "ambient" compounds) from our background reference spectra. Because of this, all measurements of methane which we report here should be read as "above or below the level of methane at the time when the background spectrum was generated". Tosco's contractor does subtract methane from all of their background files, therefore it is not a surprise to see them detecting methane more often, and at higher levels, than we do.