This newsletter is to give an insight to some concerns regarding the recovery temperatures of Method 25 trap fraction samples which have recently arisen.
There has been some discussion concerning temperatures for trap recovery. My copy of the July 1 1990 CFR indicated a heater temperature of 200o C for the trap fraction recovery, which was not to be exceeded during the recovery. I believe the pre-February 1988 version of the method had different temperature requirements, but I do not have that documentation any longer. The South Coast AQMD Method 25.1, which is based on a similar approach, has a significantly different approach to the trap recovery where the trap is heated to a “dull red” color, which would be equivalent to a temperature of about 600 o C or more.
We initially used the lower 200o C recovery temperature from the first day of operation until December 14, 1995. On that date we increased the temperature to 250o C for the recovery and we later added a clean up temperature of 350o C for all traps and an individual QC analysis of each trap while heated to a temperature of 300o C to help ensure there was no carryover between samples. Our process for any such change was and still is to perform a side by side comparison between the original procedure and the new proposed procedure. If there is no difference or there is an identified improvement as in the case of cleaning the equipment, the procedure can be accepted. I know there was discussion with the Emission Measurement Center (EMC) prior to making this particular change, but I have not been able to find the communication or documentation after seventeen years. Unless and until I can recover that communication, the supporting data we generated, or the EMC indicates there will be a change to the limits, we will retain the lower trap recovery temperature of 200o.C. The trap cleaning and QC analysis temperatures will not change and thus, are now an additional 50o C higher than the prior recovery temperature differential.
The only concern is the increased time for the trap fraction to completely elute which may increase the recovery time for that fraction and may in turn result in the pressure limits for the recovery systems/ICVs being reached prior to the complete recovery of the carbon from the trap. This occurs now, but may increase in the number of instances and the concentration of carbon in the effluent when those limits are reached.
The following information from the State of Ohio, which I believe may be followed by similar statements from other states in the future, was the final determination to make the change back to the lower recovery temperatures:
"On September 7, 2012, Central Office notified the districts that Ohio EPA will not accept Method 25 test results that use the recovery temperatures greater than the specified 200 degree Celsius temperature. It is my understanding that (at this time) US EPA is not changing the 200 degree temperature. Let me know if you have any questions."
Triangle Environmental Services, Inc.