Diffusion Scrubber Research Articles

Measurement of ambient nitrous acid and a reliable calibration source for gaseous nitrous acid

A diffusion scrubber based automated instrument measures HONO utilizing ion chromatography and UV detection with time resolutions of 7-15 min and a detection limit of ca. 20 pptv. The thermodynamic equilibrium of NH{sub 3}(g) and HONO(g) over NH{sub 4}NO{sub 2}(s) can be described by ln (p{sub HONO}, atm) = {minus}8,018 {plus minus} 84/T + 16.81 {plus minus} 0.30 and provides a convenient and reliable source for HONO(g) free from major contamination with NO{sub x}. Ambient measurement data for Lubbock, TX, are presented. Persistent daytime concentrations of HONO in the 100-500 pptv range, weekday morning peak concentrations up to 1 ppbv following peak traffic hours, and typical nighttime peak concentrations between 1 and 2 ppbv are observed.

Design of a straight inlet diffusion scrubber. Comparison of particle transmission with other collection devices and characterization for the measurement of hydrogen peroxide and formaldehyde

Particle deposition characteristics of several diffusion scrubber (DS) designs of annular geometry were studied and a straight inlet geometry was selected for further performance evaluation. At sample flow rates of 1–5 ℓ min −1, 5–17% of Boltzmann charged 0.1–3 μm aerosol is deposited in the device, with 0.5–2.5% deposition on the membrane tube, the central collecting element. Most of the wall deposition appears to be due to electrostatic effects caused by the PTFE wall; this is accentuated by dry air (⩽5% r.h.) test conditions. Significant deposition loss is observed with glass denuders under the same test conditions as well. Extensive performance tests were made with the new geometry DS; Nafion® membrane based DS devices are recommended for the measurement of H 2O 2 and HCHO. For NH 3, reasonably fast response times are difficult to attain with Nafion membrane DS devices, however. Some unexpected new findings regarding the transmission of acid gases through a Nafion membrane and their implications are discussed.

AN AUTOMATIC MEASUREMENT OF GASEOUS NITRIC ACID IN THE URBAN ATMOSPHERE BY COMBINATION OF A DIFFUSION SCRUBBER AND ION CHROMATOGRAPHY

In this study, an automatic measurement of HNO3 was investigated by using a diffusion scrubber and ion chromatography. The collection efficiency of HNO3 standard gas of 36μg/m3 was 93.1±3.3% (n=4) by using 50cm lengh of the diffusion scrubber at 1_??_/min of air flow. The lower detection limit of HNO3 by this method was 0.01μg/m3 at sampling volume of 60Å The concentration of HNO3 in the urban atmosphere is a few μg/m3 It is suitable for this method to measure HNO3 at ambient level.

Formaldehyde Measurement Methods Evaluation and Ambient Concentrations During the Carbonaceous Species Methods Comparison Study

During the Carbonaceous Species Methods Comparison Study at Glendora, CA, six groups made independent measurements of ambient formaldehyde concentrations during the period August 11–21, 1986. Measurement methods included DNPH-impregnated cartridges, an enzymatic technique, a diffusion scrubber, Fourier transform infrared spectroscopy (FTIR), differential optical absorption spectroscopy (DOAS), and tunable diode laser absorption spectroscopy (TDLAS). Sufficient data were obtained over the 10-day period to assess differences among methods based on hourly averages, 4- and 8-hour time-integrated sampling periods, and 3–5-minute averaging times. Comparison among the three spectroscopic methods (DOAS, FTIR, and TDLAS) showed good agreement, within 15% of the mean of the three methods for 162 hourly values. The enzymatic technique and diffusion scrubber reported concentrations ∼ 25% higher and 25% lower than the spectroscopic mean, respectively, for the entire study period. The DNPH cartridges, the only routine monitoring method in the study, yielded values 15–20% lower than the spectroscopic mean, with somewhat lower values over longer sampling periods. Measurement response time was not a factor for either the FTIR or the TDLAS methods. Formaldehyde exhibited a morning and an afternoon peak each day during the study. The morning peak was shown to be associated with NOx and particulate black carbon concentrations; the afternoon peak was associated with the arrival of photochemically produced ozone at the site. The maximum peak hourly average, reported as the mean of the three spectroscopic methods, was 20 ppb; the average nighttime minimum was 6 ppb. These data suggest that primary formaldehyde may be a greater contributor to total formaldehyde levels than previously thought.

Measurement of Hydrogen Peroxide in Ambient Air by Impinger and Diffusion Scrubber

Two methods for the determination of gaseous hydrogen peroxide in ambient air were tested during the Carbon Species Methods Comparison Study conducted at Glendora, CA, August 12–20, 1986. Air was sampled by the BNL dual impinger/diffusion scrubber apparatus after ambient ozone removal by addition of NO. Sampling was done during daylight hours (∼ 0800–2000 hours) from a sampling line shared with the National Center for Atmospheric Research (NCAR) and Texas Tech University (TTU) groups. Impinger data were formally compared with results from other methods; they showed afternoon maxima which were generally 1 ppbv the last 4 days of the study, respectively. Data from the diffusion scrubber agreed well with the impinger data if the former are corrected for an ∼ 40% aqueous phase loss of collected H2O2. Error sources for impinger and scrubber data resulting from potential interferences and loss mechanisms are discussed. By acceptance of this article, the publisher and/or reci...

Diffusion Scrubber-Based Field Measurements of Atmospheric Formaldehyde and Hydrogen Peroxide

Field measurements were conducted to determine atmospheric concentrations of HCHO and H2O2 with automated instrumentation that relies on diffusion-based collection of water-soluble gases by an aqueous absorber flowing through a hydrophobic porous membrane tube. These measurements were made as part of the Carbonaceous Species Methods Comparison Study (CSMCS) at Cirrus College, Azusa, CA, during August 12–20, 1986. Both HCHO and H2O2 showed marked diurnal cycles, decreasing at night (to a minimum of 2–4 ppbv for HCHO, and near the detection limit, ∼ 30 pptv for H2O2) and increasing to a maximum in the late afternoon (15–19 ppbv for HCHO, ∼ 2 ppbv for H2O2). For the most part, the instrumentation performed unattended as designed; however, particle deposition in sampling lines and in the membrane-based diffusion scrubbers suggest that in-line losses can be significant for continued sampling of ambient air containing a relatively high concentration of particulate matter. Periodic (e.g., daily or every 2 days) ...

Inlet pressure effects on the collection efficiency of diffusion scrubbers

Inlet pressure effects on the collection efficiency of diffusion scrubbers

Measurement of atmospheric sulfur dioxide by diffusion scrubber coupled ion chromatography

A porous membrane diffusion scrubber designed to collect soluble atmospheric gases without obligatory collection of particulate material has been coupled to an ion chromatograph in a continuous automated manner. With 1 mM H/sub 2/O/sub 2/ used as the scrubber liquid, the collected S(IV) is oxidized to sulfate and determined as such. The instrument operates on a 6-min cycle. During most of this period, the loop of the chromatographic valve is slowly filled with the scrubber effluent. Following a brief stay in the inject position, the valve returns to the load position again. The desired chromatographic separation is accomplished within the cycle time. Thus, a new chromatogram is produced every 6 min. Based on the standard deviation of the blank, the detection limit is better than 20 parts per trillion by volume (pptrv) SO/sub 2/; the lowest standard concentration studied was 77 pptrv. Ambient SO/sub 2/ determination results are presented. The potential of simultaneous determination of several other gases is obvious.

A numerical solution for mass transport in membrane-based diffusion scrubbers

La methode des elements finis est utilisee pour resoudre les problemes de diffusion a travers une paroi poreuse d'un composant simple dans un fluide en ecoulement laminaire. Ce type de phenomene est rencontre dans des laveurs a membrane utilises pour des separations gaz-liquide ou liquide-liquide

Continuous liquid-phase fluorometry coupled to a diffusion scrubber for the real-time determination of atmospheric formaldehyde, hydrogen peroxide and sulfur dioxide

An aqueous scrubber liquid is pumped through a filament-filled narrow bore microporous hydrophobic membrane tube while sample air flows around it. A constant fraction of the analyte gas, dependent on its diffusion coefficient and the effective mass accommodation coefficient in the scrubber liquid and on the diffusion scrubber dimensions and sampling rate, is collected in the liquid. One or more reagents are added to the effluent liquid for specific determination of the gas of interest. The Hantzsch reaction, peroxidase-mediated oxidation of p-hydroxyphenylacetic acid by peroxide, and bisulfite addition to 9- N-acridinylmaleimide, all direct adaptations of previously described continuous flow aqueous analytical procedures, are used for the determination of HCHO, H 2O 2 and SO 2, respectively. A permeation-based SO 2 source and previously described Henry's Law-based porous membrane sources of HCHO and H 2O 2 are integral to the respective instruments for calibration. Programmed inert valves allow the instruments to perform any sequence of zero, calibrate and sample functions. Each instrument occupies a standard two-tier (50×100 cm) laboratory cart and has been successfully field tested. With a filter fluorometer as detector, LODs are 100 pptv HCHO, 30 pptv H 2O 2 and 175 pptv SO 2. There is no significant dependence on relative humidity. Specific interference testing ( SO 2 O 3 for HCHO and H 2O 2, O 3 H 2O 2H 2SCH 3SH for SO 2) reveals no major interferences.

Sampling and determination of gas-phase hydrogen peroxide following removal of ozone by gas-phase reaction with nitric oxide

A method for the determination of hydrogen peroxide in the ambient atmosphere is described, using impinger or diffusion scrubber collection of H/sub 2/O/sub 2/ with aqueous-phase analysis by an enzyme-catalyzed fluorescence technique. Interference from ozone at ambient levels is removed by gas-phase reaction with excess nitric oxide. The impinger and diffusion scrubber collection techniques give equivalent results for atmospheric gas-phase H/sub 2/O/sub 2/ with limits of detection of 0.1 ppbv for approximately 60-min and 10-min sampling times, respectively.

Porous membrane-based diffusion scrubber for the sampling of atmospheric gases

A diffusion scrubber, employing a porous fluorocarbon membrane as the sampling tube and with a scrubber solution flowing into a narrow annular space exterior to the membrane, is described. The use of this diffusion scrubber with a dilute buffered formaldehyde solution as the scrubber solution has been exploited for collecting sulphur dioxide. Collection efficiencies are reported for sampling rates of up to 3 l min–1. The response time to a SO2 input pulse in the continuous analysis mode is demonstrated using dilute hydrogen peroxide as the scrubber solution and a conductivity detector. The advantages of a diffusion scrubber for collecting atmospheric gases are discussed. A simple inexpensive design of permeation tubes for standard gas sources is also reported.

A diffusion scrubber for the collection of atmospheric gases

A diffusion denuder, with a thin membrane tube as the collecting element and with a scrubber solution flowing in a narrow annular gap outside the membrane is described. The use of this diffusion scrubber with a cation exchange membrane in conjunction with a dilute acid scrubber has been exploited for collecting ammonia. The advantages of the diffusion scrubber as a highly efficient concentrator of soluble atmospheric gases and as an integral part of a microflow continuous flow analysis system are discussed.

Long‐term clearance of inhaled diesel exhaust particles in rodents

The fate of inhaled diesel exhaust particles was studied in male Fischer 344 rats and Hartley guinea pigs using radioactive diesel particles, tagged in the insoluble particulate core with 14C and generated from a single-cylinder diesel engine. The potential artifact of increased radioactivity due to the absorption of 14CO2 in the blood was minimized by passing the exhaust through a diffusion scrubber prior to its dilution and introduction into a nose-only exposure chamber. Disappearance of the inhaled 14CO2 from blood through the expired air and urine was rapid, indicating that a correction for the increased radioactivity was necessary only for tissue samples generated during the first day after the exposure. An atomic absorption spectrophotometric method was developed to determine the amount of blood and, thus, its contribution of 14CO2 activity in excised organs and tissues. Fischer rats exposed to diluted diesel exhaust at 2 particulate concentrations with similar total inhaled dose (7 mg/m3 for 45 min, and 2 mg/m3 for 140 min) had comparable deposition efficiencies and showed no significant difference in particle clearance for data measured up to 1 yr after the exposure. Long-term retention of inhaled diesel particles in Fischer rats, measured up to 330 d after the exposure, was analyzed as 3 clearance phases with half-times of 1 d, 6 d, and 80 d, respectively. In contrast, very little clearance was observed in guinea pigs between d 10 and d 432 after the exposure, and only the early clearance phase can be represented by a single exponential curve with a half-time of 1-2 d.