1998 Progress Report: Measurements of Non-Methane Volatile Organic Compounds in the Lower Troposphere From Tethered Balloon and Kite Sampling Platforms by Internal Standard Calibration Using Ambient CFC Reference CompoundsEPA Grant Number: R825417
Title: Measurements of Non-Methane Volatile Organic Compounds in the Lower Troposphere From Tethered Balloon and Kite Sampling Platforms by Internal Standard Calibration Using Ambient CFC Reference Compounds
Investigators: Helmig, Detlev , Balsley, Ben , Birks, John , Karbiwnyk, Christine
Current Investigators: Helmig, Detlev , Balsley, Ben , Birks, John , Karbiwnyk, Christine , Mills, Craig
Institution: University of Colorado at Boulder
EPA Project Officer: Hunt, Sherri
Project Period: October 1, 1996 through September 30, 1999
Project Period Covered by this Report: October 1, 1997 through September 30, 1998
Project Amount: $436,172
RFA: Analytical and Monitoring Methods (1996) RFA Text | Recipients Lists
Research Category: Environmental Statistics , Air Quality and Air Toxics , Water , Land and Waste Management , Air , Ecological Indicators/Assessment/Restoration
Objective:The main goal of this project is to develop an analytical method for the analysis of atmospheric volatile organic compounds (VOCs) using atmospheric chlorofluorocarbons (CFCs) as internal standard compounds. This technique will allow the development of low-cost, light-weight, and battery powered sampling packages to analyze VOCs in atmospheric samples from airborne sampling platforms such as tethered balloons and light aircraft. Along the way to achieving these goals, solid adsorbent sampling methods are investigated for their reproducibility in the analysis of selected CFCs and VOCs.
Progress Summary:Construction of the 10 port sampler was completed. This instrument facilitates sampling of a mass flow controlled air stream through a two-way valve that switches from a sampling stream to a vented stream. An additional 10 port multi-position valve switches between cartridges for sampling. This set-up insures isolation of the cartridges before and after sampling. These electronically actuated valves may be operated manually or by serial communication. A laptop computer was purchased and a program was written for sequential sampling. This has allowed accurately timed sampling in the laboratory and will be used for sampling aboard light aircraft in the future.
A new light-weight, battery powered sampling package for attachment to a balloon tether line has been developed in collaboration with A. P. Buck, Inc. (Orlando, FL). Six of these Buck-Genie Lo-Flo? pumps were purchased. These pumps are fully programmable and can be operated in constant flow or constant pressure mode. They also correct for changes in pressure and temperature. These pumps will be used as part of the single cartridge sampling package on the balloon tether line and also as part of the airborne balloon sampler that holds 8 cartridges. Construction of this sampler and its electronic controls were completed. Solenoid valves are triggered by remote control after programming the sampling times for each cartridge. This sampler will allow sampling at one altitude over time as well as sampling individual cartridges at different altitudes during assent or decent of the balloon.
Construction of a humidifier that utilizes a micro-porous PTFE tube (International Polymer Engineering; Tempe, AZ) surrounded by water to humidify a sample air stream was completed. Experiments with humidified samples have begun. Current experiments are designed to measure the uptake of water on the cartridges, and water interference on detector response and peak shape at different humidity levels. This system will also aid in optimizing ATD-400 desorption parameters in order to prevent an ice plug from forming at the head of the column. In addition, water management methods for drying humid samples will be explored.
Two 11 liter aluminum cylinders received Accu-Life? treatment from Scott Specialty Gases to deactivate the cylinder walls. A VOC standard was prepared in one of these cylinders by diluting a liquid hydrocarbon mixture with ultra pure nitrogen gas. This standard was purchased from Supelco (Bellefonte, PA) and contains n-Propane, 2-Methylpropane, n-Butane, 2-Methylbutane, n-Pentane, 2-Methylpentane, n-Hexane, 2,4-Dimethylpentane, n-Heptane, Toluene, n-Octane, p-Xylene, n-Propylbenzene, n-Decane, n-Butylbenzene, n-Dodecane, n-Tridecane, n-Tetradecane and n-Pentadecane. Current GC parameters allow the separation of n-Propane through n-Butylbenzene. Concentrations of the compounds in this gas standard were confirmed by measurements made by Dr. Paul Goldan and Dr. Bill Kuster at the National Oceanic and Atmospheric Association (NOAA) Boulder, CO.
A certified TO-14 gas standard (Scott Specialty Gases) was purchased from Supelco (Bellefonte, PA) and diluted with ultra pure nitrogen gas. This standard contains 39 compounds including CFCs 11, 113, 114 and 12, VOCs, chlorinated VOCs and bromomethane. Cartridges loaded with this standard have undergone GC/MS analysis for peak confirmation and GC/FID/ECD for quantitative analysis. Further testing and analysis of this standard is in progress.
Precision testing of these standards revealed inaccuracies for heavy hydrocarbons. ATD-400 desorption parameters have been changed in an effort to optimize desorption of the heavy hydrocarbons and improve the precision of these compounds. In addition, the precision of ambient hydrocarbon quantitation using ambient CFCs as reference compounds was examined. Table 1 shows the relative standard deviation of the peak area ratios of hydrocarbons to CFCs from the analysis of an urban air sample. Air was collected into a 100 liter Teflon bag and 5 liter aliquots were loaded onto 10 adsorption cartridges. Achievable precision reflects recovery, sample breakthrough, GC resolution and detector response. For the majority of VOCs investigated, precision levels on the order of 1-3% are feasible under these conditions.
Table 1: Relative standard deviation (in %) of the peak area ratio of hydro- carbons (FID signal) to CFCs (ECD signal) in an ambient air sample.