Grantee Research Project Results
1999 Progress Report: Techniques for Standardization, Validation, and Measurement of Targeted Trace Gases Which Participate in Tropospheric Ozone Formation
EPA Grant Number: R825261Title: Techniques for Standardization, Validation, and Measurement of Targeted Trace Gases Which Participate in Tropospheric Ozone Formation
Investigators: Apel, Eric C. , Fried, Alan , Gilpin, Tim
Current Investigators: Apel, Eric C. , Gilpin, Tim , Fried, Alan , Riemer, Dan
Institution: National Center for Atmospheric Research
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1997 through December 31, 1999
Project Period Covered by this Report: January 1, 1999 through December 31, 2000
Project Amount: $472,250
RFA: Air Quality (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The research objectives cover three distinct areas: (1) development of necessary standards for target oxygenated volatile organic compounds (OVOCs); (2) development of accurate analytical methods, including a formaldehyde method, to verify the standards and to lay the groundwork for reliable ambient measurements; and (3) development of a calibration facility whereby university researchers, including PAMS personnel (cartridges), may come to calibrate and test their instruments under simulated ambient conditions.Progress Summary:
Progress has been made towards accomplishing the objectives in the three areas described above. Our formaldehyde system (Hantzsch) was fully developed and brought online to monitor permeation standards, and we developed a technique to make stable formaldehyde standards in high-pressure cylinders. At this point, we have investigated several methods for the preparation and analysis of standards. Part of the work in this proposal was based on the premise that independent methods of standards generation and analysis that agree increase the confidence in the overall accuracy of the standards. We have constructed and employed a 6-position device for a standards generation system based upon permeation tubes and employing gravimetry as the method of calibration. The compounds for which we created permeation tubes are methanol, acetaldehyde, propanal, acetone, methyl ethyl ketone, and toluene. This system consists of six independent aluminum ovens, each housing one permeation tube. The ovens are temperature controlled to within ? 0.1oC. The tubes are contained in glass housings with high purity nitrogen continuously flowing over them. A dynamic dilution system has been constructed to control, mix, and dilute the permeation tube effluent to the ppmv to ppt range of concentrations. Although the tubes are factory calibrated, we are also characterizing them using a Mettler balance capable of measuring to ? 10 mg.We have also prepared a number of high-pressure ppmv and ppbv standards with two independent techniques described in the previous year's report.
Verification of the Accuracy of the Standards. Methods have been developed to verify the accuracy of our standards. A GC-FID system developed in the previous year is used to compare the high-pressure cylinders with the permeation tubes. The top panel in Figure 1 below shows our analysis of the six tubes at once; however, it should be noted that for quantification our normal procedure is to run each permeation tube separately using a highly characterized diluent flow rate. The bottom panel shows our analysis of a high-pressure cylinder that was prepared containing acetaldehyde, methanol, ethanol, propanal, acetone, butanal, and methyl ethyl ketone. Note that all compound peaks are well resolved and easily quantified.
Figure 1. Top panel: Chromatogram showing analysis of permeation tubes. Bottom panel: Chromatogram showing the analysis of the high-pressure cylinder standard.
Together with the GC-FID analysis, an independent spectroscopic (FTIR) method has also been developed and used to ascertain the concentrations in the high-pressure cylinder. Table 1 shows the results of the comparison of the high-pressure cylinder preparation results with the permeation tubes and the FTIR analysis. Good comparability is observed for the cylinder preparation and the permeation tubes for methanol and acetone. We do not have reliable permeation tube values for acetaldehyde and propanal. We found that although the initial values we obtained were close to the manufacturer's certified rate, the permeation rate of these increased as a function of time. This is despite the fact that we used N2 sweep gas and maintained the permeation tubes at 30?C. The manufacturer (VICI) is aware that there is a problem with the aldehyde perm tubes and is working with us to help resolve it. There are no permeation tube values for MEK as of yet because we have only recently put this tube into our system and have not had it long enough to get an accurate weight loss over time.
The FTIR values agree within the error of the measurement with the gravimetric cylinder values for all compounds measured, except for MEK. The reasons for this are unclear and we will investigate this result further.
It is important that the compounds are stable in the cylinders. Table 2 shows our analyses, taken almost 6 months apart, of some of the compounds relevant to this proposal. These compounds showed excellent stability. Except for methanol (-7.1 percent), all compounds agreed to within 5 percent for the two analyses.
Table 2. Stability of Alcohol and Carbonyl Standards in High Pressure Cylinders
*analysis based on relative calibration factors
from FID and represent an average of 3 chromatographic runs.
A GC/MS system was developed for measuring OVOCs as detailed in the previous year's report. The system was optimized for resolution and time response for a number of OVOCs. Figure 2 below shows a chromatogram of an NCAR-prepared OVOC standard. The specificity is excellent with this type of analysis because compounds are separated chromatographically and the ions detected are specific to the compound whose retention time is known.
Figure 2. GC/MS run of 7-component standard. An 60m HP-624 column was used.
The system was brought into the field in 1999 for testing and analysis. Figure 3 below shows a typical analysis of select compounds of an air sample obtained during the SOS-Nashville study.
Figure 3. GC/MS Analysis of rural air outside of Nashville TN.
Detection limits are good for this instrument. For a 300 mL sample, detection limits were for the compounds shown: acetaldehyde - 5 pptv, methanol - 30 pptv, ethanol - 25 pptv, propanal - 4 pptv, acetone - 4 pptv, butanal - 12 pptv, and MEK - 8 pptv. The system was calibrated with NCAR high-pressure standards and a rack-mountable dilution system.
Future Activities:
We will continue to progress as specified in our proposal. We will continue to develop the multi-technique approach to generate high quality OVOC standards and validate them with state-of-the-art techniques.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 9 publications | 4 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Apel EC, Calvert JG, Riemer D, Pos W, Zika R, Kleindienst TE, Lonneman WA, Fung K, Fujita E, Shepson PB, Starn TK, Roberts PT. Measurements comparison of oxygenated volatile organic compounds at a rural site during the 1995 SOS Nashville Intensive. Journal of Geophysical Research-Atmospheres 1998;103(D17):22295-22316. |
R825261 (1997) R825261 (1998) R825261 (1999) R825261 (Final) |
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Supplemental Keywords:
media, chemicals, toxics, toxic substances, methods/techniques., RFA, Scientific Discipline, Air, Geographic Area, air toxics, Environmental Chemistry, State, tropospheric ozone, Atmospheric Sciences, EPA Region, monitoring, interferents, Henry's Law, aldehydes, ketone, National Center for Atmospheric Research, ozone formation, atmospheric chemical cycles, Region 8, standardization techniques, atmospheric monitoring, Colorado (CO), ozone production, trace gas measurementProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.