Karen D. Oliver

SAMPLE INTEGRITY OF TRACE LEVEL VOLATILE ORGANIC COMPOUNDS IN AMBIENT AIR STORED IN SUMMA@ POLISHED CANISTERS

Abstract Sets of new and used SUMMA® polished stainless steel canisters were tested for storage stability of volatile organic compounds (VOCs). Evacuated canisters were filled at a controlled rate with ambient air containing added concentrations of 15 VOCs (14 chlorinated, one brominated) at

Technique for monitoring ozone precursor hydrocarbons in air at photochemical assessment monitoring stations: Sorbent preconcentration, closed-cycle cooler cryofocusing, and GC-FID analysis

Abstract An automated gas chromatograph (autoGC) system that may be used to collect and analyze both polar and nonpolar volatile organic compounds in ambient air has been evaluated. This system combines the use of dual multiadsorbent traps for sampling 57 min h −1 at ambient temperature, a dry helium purge to remove residual water from the sorbents, thermal desorption of analytes onto a Stirling-cooled trap for refocusing, and GC-flame ionization detection (FID). Method detection limits (MDLs), linearity, cleanliness, precision, and accuracy of the autoGC were determined for a set of 57 ozone precursor hydrocarbons. For most of the compounds tested, MDLs were less than 0.40 ppbv, the FID response was linear over the 5–40-ppbv range, and the trap-to-trap precision was ± 10%. This autoGC was found to be a reliable system that would be suitable for use in field sites such as the Photochemical Assessment Monitoring Stations network, which is being implemented in the United States of America.

24 h diffusive sampling of toxic VOCs in air onto Carbopack X solid adsorbent followed by thermal desorption/GC/MS analysis-laboratory studies.

Diffusive sampling of a mixture of 42 volatile organic compounds (VOCs) in humidified, purified air onto the solid adsorbent Carbopack X was evaluated under controlled laboratory conditions. The evaluation included variations in sample air temperature, relative humidity and ozone concentration. Linearity of samples with loading was examined both for a constant concentration with time varied up to 24 h and for different concentrations over 24 h. Reverse diffusion and its increase with accumulation of sample were determined for all compounds. Tubes were examined for blank levels, change of blanks with storage time, and variability of blanks. Method detection limits were determined based on seven replicate samples. Based on this evaluation, 27 VOCs were selected for quantitative monitoring in the concentration range from approximately 0.1 to 4 ppbv. Comparison results of active and diffusive samples taken over 24 h and under the same simulated ambient conditions at a constant 2 ppbv were interpreted to estimate the effective diffusive sampling rates (ml min(-1)) and their uncertainties and to calculate the corresponding diffusive uptake rates (ng ppmv(-1) min(-1)).

Analysis of VOCs in Ambient Air Using Multisorbent Packings for VOC Accumulation and Sample Drying

Abstract Solid multisorbent packings have been characterized for trapping and release efficiency of trace (10-20 ppbv in humidified zero air) volatile organic compounds (VOCs). The use of a two-stage trapping system reduces sample water content typically by more than 95.5% while maintaining a trapping and release efficiency of 100% for 49 VOCs, including eight water-soluble VOCs. Three combinations of primary tube and focusing tube are examined in detail by using an atomic emission detector to monitor hydrogen as an indication of residual water vapor, and to monitor either chlorine, bromine, or carbon for target VOCs. Linearity of response to individual VOCs, the presence of artifacts, and a laboratory monitoring application are also discussed.

Volatile organic compound concentration patterns at the New Hendersonville monitoring site in the 1995 Southern Oxidants Study in the Nashville, Tennessee, area

Ambient gaseous organic compounds were monitored on an hourly basis with an automated gas chromatograph from June 15 to 27, 1995, at the New Hendersonville site near Nashville. Tennessee. as part of the Southern Oxidants Study (SOS). These compounds and their estimated average contributions to the total were as follows: isoprene (2.1 ppbC), methyl vinyl ketone (1.1 ppbC), methacrolein (0.6 ppbC), α-pinene plus β-pinene (1.3 ppbC), and those nonmethane hydrocarbons, minus isoprene, monitored routinely in the Photochemical Assessment Monitoring Stations (44.6 ppbC). The sum of n-aldehydes from butanal through nonanal averaged 12.6 ppbC, where a conservative estimate of artifact n-aldehydes has been subtracted. Strong diurnal variations in the concentrations of n-aldehydes and the apparent influence of wind shifts on concentration support the existence of n-aldehydes at significant levels in the ambient air. The empirical fit to data as developed by Jobson et al. [1994] was the upper bound to the loci of maximum isoprene concentrations as a function of temperature and the diurnal variation of the ratio of methyl vinyl ketone to methacrolein was similar to that in studies by Montzka et al. [1993] in the rural southeastern Unitcd States. The α-pinene and β-pinene concentrations were proportional and α-pinene concentrations always less than 2 ppbC. In supplemental experiments at a rural site in North Carolina. the α-pinene concentrations showed a distinctive diurnal pattern with high nighttime values and low midday values. Patterns of concentration for the anthropogenic hydrocarbons benzene, toluene, and o-xylene versus wind direction showed the impact of a major toluene-emitting source as well as the influence of emissions from the direction of Nashville.

Enhanced Performance of Nafion Dryers in Removing Water from Air Samples Prior to Gas Chromatographic Analysis

Nafion tube dryers were tested for applications of sample preparation prior to gas chromatographic analysis. Steady-state and timedependent drying efficiency were measured for four similar dryers using a 50-mL/min sample flow at 95 percent relative humidity at room temperature. A procedure was developed in which water removal efficiency was temporarily enhanced by a factor of 20 as compared with the steady state. This was accomplished by heating the dryer while purging it with a dry sample stream immediately prior to processing the gas sample of interest. The procedure was tested on an automated gas chromatographic system equipped with a cryogenic sample preconcentrator. Data for 15 volatile organic compounds of interest showed no effect of this procedure on sample integrity; some improvement in run-to-run precision was observed.

Estimating common parameters of lognormally distributed environmental and biomonitoring data: Harmonizing disparate statistics from publications

The progression of science is driven by the accumulation of knowledge and builds upon published work of others. Another important feature is to place current results into the context of previous observations. The published literature, however, often does not provide sufficient direct information for the reader to interpret the results beyond the scope of that particular article. Authors tend to provide only summary statistics in various forms, such as means and standard deviations, median and range, quartiles, 95% confidence intervals, and so on, rather than providing measurement data. Second, essentially all environmental and biomonitoring measurements have an underlying lognormal distribution, so certain published statistical characterizations may be inappropriate for comparisons. The aim of this study was to review and develop direct conversions of different descriptions of data into a standard format comprised of the geometric mean (GM) and the geometric standard deviation (GSD) and then demonstrate how, under the assumption of lognormal distribution, these parameters are used to answer questions of confidence intervals, exceedance levels, and statistical differences among distributions. A wide variety of real-world measurement data sets was reviewed, and it was demonstrated that these data sets are indeed of lognormal character, thus making them amenable to these methods. Potential errors incurred from making retrospective estimates from disparate summary statistics are described. In addition to providing tools to interpret “other people’s data,” this review should also be seen as a cautionary tale for publishing one’s own data to make it as useful as possible for other researchers.

Ozone reaction with n-aldehydes (n=4-10), benzaldehyde, ethanol, isopropanol, and n-propanol adsorbed on a dual-bed graphitized carbon-carbon molecular sieve adsorbent cartridge.

Ozone reacts with n-aldehydes (n=4-10), benzaldehyde, ethanol, isopropanol and n-propanol adsorbed on a dual-bed graphitized carbon-carbon molecular sieve adsorbent cartridge. Destruction of n-aldehydes increases with n number and with ozone concentration. In some sampling experiments both generation and destruction of n-aldehydes by ozone are observed. In field experiments the results of sample analysis for n-aldehydes and benzaldehyde are frequently not proportional to sample volume whereas results for toluene and isoprene, and sometimes for total carbon, are. A simple theory is developed to simulate the net result of three processes: the adsorption of compounds from an air stream onto a solid adsorbent, the generation of compounds by reaction of ozone with materials upstream of or on the adsorbent, and the destruction by ozone of pre-existing compounds and compounds adsorbed from the sample stream. The use of distributed volume pairs is recommended as a way to identify loss of sample integrity during air monitoring experiments.

Volatile organic compounds at two oil and natural gas production well pads in Colorado and Texas using passive samplers.

ABSTRACT A pilot study was conducted in application of the U.S. Environmental Protection Agency (EPA) Methods 325A/B variant for monitoring volatile organic compounds (VOCs) near two oil and natural gas (ONG) production well pads in the Texas Barnett Shale formation and Colorado Denver–Julesburg Basin (DJB), along with a traffic-dominated site in downtown Denver, CO. As indicated in the EPA method, VOC concentrations were measured for 14-day sampling periods using passive-diffusive tube samplers with Carbopack X sorbent at fenceline perimeter and other locations. VOCs were significantly higher at the DJB well pad versus the Barnett well pad and were likely due to higher production levels at the DJB well pad during the study. Benzene and toluene were significantly higher at the DJB well pad versus downtown Denver. Except for perchloroethylene, VOCs measured at passive sampler locations (PSs) along the perimeter of the Barnett well pad were significantly higher than PSs farther away. At the DJB well pad, most VOC concentrations, except perchloroethylene, were significantly higher prior to operational changes than after these changes were made. Though limited, the results suggest passive samplers are precise (duplicate precision usually ≤10%) and that they can be useful to assess spatial gradients and operational conditions at well pad locations over time-integrated periods. Implications: Recently enacted EPA Methods 325A/B use passive-diffusive tube samplers to measure benzene at multiple fenceline locations at petrochemical refineries. This pilot study presents initial data demonstrating the utility of Methods 325A/B for monitoring at ONG facilities. Measurements revealed elevated concentrations reflective of production levels and spatial gradients of VOCs relative to source proximity at the Barnett well pad, as well as operational changes at the DJB well pad. Though limited, these findings indicate that Methods 325A/B can be useful in application to characterize VOCs at well pad boundaries.

Optimizing Sensitivity of SIM Mode of GC/MS Analysis for EPA’s TO-14 Air Toxics Method

Guidelines for determining volatile organic compounds (VOCs) at ambient levels In air are published In Method TO-14 ol the U.S. Environmental Protection Agency’s “Compendium 01 Methods lor the Determination of Toxic Organic Compounds In Ambient Air.” To achieve the sensitivity required for sub-part-per-bllllon-by-volume (ppbv) determinations of VOCs, TO-14 recommends selective Ion monitoring (SIM) mode of operation when a conventional quadru-pole mass spectrometer Is used as the analytical finish. This paper describes the Implementation of SIM mode of analysis and presents the rationale and methods for optimizing SIM parameters for maximum sensitivity when analyzing whole-air samples for trace levels of targeted VOCs.