Diffusion Scrubber Research Articles

Conductometric Determination of Ammonium in Turbid Water with a Flow-batch Porous Membrane-based Diff usion Scrubber System

A porous membrane-based diffusion scrubber was fabricated to couple with a conductometric detector as a fl ow-batch system for determining ammonium in turbid surface waters. A gravity fl ow of DI water as a gas absorbing liquid and a manual sample introduction was employed to develop a cost- effective device without using a conventional pump and an injection valve. The standard calibration graph was linear in the range of 5 – 100 μmol L-1, with a relative standard deviation of < 5%. The detection limit based on the lowest concentration in the calibration graph of 5 μmol L-1 can be obtained. The results of ammonium determination using the proposed method agree well with those using the batch-wise indophenol blue as a standard method. The proposed analytical system provides a cost-effective setup and easy operation for ammonium determination in some turbid surface waters samples without requiring a fi ltering process and conventional glassware.

Colorimetric Determination of Sulfide in Turbid Water with a Cost-effective Flow-batch Porous Membrane-based Diffusion Scrubber System.

A cost-effective flow-batch analysis approach with colorimetric measurement has been developed for sulfide ion determination in turbid water samples without using a conventional pump and valve. Under an acidic condition, sulfide ion was converted to hydrogen sulfide gas and liberated out from other complicated matrices. The porous membrane-based diffusion scrubber was utilized as a gas trapping unit for hydrogen sulfide gas separation/preconcentration. From the correlation of sulfide ion concentration and disappearance of sodium nitroprusside reagent detection by using a homemade LED-photodiode based colorimetry, a linear relationship of sulfide ion concentration and absorbance can be obtained with relative standard deviation (%RSD) less than 5%. The limit of detection was 5.6 μmol L-1. The proposed system was applied for sulfide ion determination in wastewater samples with the recoveries of 91.0 - 105.2%. The proposed system is a robust setup and able to handle turbid water samples without a sample filtering step.

A-14 拡散スクラバー法による室内空気汚染物質の除去装置の研究 : その3 可搬型除去装置によるホルムアルデヒドの除去

A-14 拡散スクラバー法による室内空気汚染物質の除去装置の研究 : その3 可搬型除去装置によるホルムアルデヒドの除去

Portable analyzer for continuous monitoring of sulfur dioxide in gas stream based on amperometric detection and stabilized gravity-driven flow

The construction, optimization and application are described for a portable gas analyzer which gives real-time measurement of sulfur dioxide in a gas stream. The SO2 is absorbed from the analyte gas stream into a gravity-driven carrier solution flowing through a diffusion scrubber (DS), in the form of a bundle of polymeric hollow fibers. The sulfite ions in the carrier solution are detected by anodic amperometry at a novel carbon nanotube (CNT) electrode polarized at 0.35V vs Ag/AgCl reference electrode. A novel compact design is the result of integrating the DS with the amperometric detector and yields a light weight portable analyzer (900g) with a small footprint. The optimized analyzer has favorable performance characteristics such as (i) good sensitivity (LOD=4ppm, S/N=3), (ii) wide linear dynamic range up to 5000ppm, (iii) reasonably fast response time (t95%, 4.1min), (iv) excellent signal stability and repeatability (RSD=1.3%), and (v) continuous standalone operation for 6h. The interfering effect of H2S is avoided by removing H2S using a prior guard column. The analyzer can successfully monitor the removal of SO2 from SO2-N2 gas mixtures and in determining sulfite in foodstuffs.

Development of environmental measurement technology for air pollution gases and air cleaning technology by the diffusion scrubber method

Development of environmental measurement technology for air pollution gases and air cleaning technology by the diffusion scrubber method

Portable dual-channel gas analyzer for continuous monitoring of carbon dioxide in gas streams

Abstract Development, characterization and application of a portable dual-channel analyzer based on gravity driven flow for continuous monitoring of CO2 in gas streams are presented. The analyzer is constructed from (i) a carrier/stripping solution reservoir, (ii) a diffusion scrubber (DS) in the form of a hollow fiber membrane (HFM) module integrated with a custom-designed flow-through pH-detector cell, and (iii) a waste solution reservoir. The analyzer is designed in such a way that the dilute sodium bicarbonate carrier/stripping solution flows downward by gravity into the lumen side of the hollow fibers in the HFM module which allows efficient contact with the gas stream. Absorption of CO2 into the carrier solution produces pH changes that constituted the analytical signal. Flat-bottom glass electrode and solid-state IrO2 electrodes were used as pH detectors in two types of custom-built flow cells, respectively. Under the optimized conditions, the measured pH signal showed Nernstian response to the CO2 concentration (59.6 and 62.0 mV/log[CO2] and r2 = 0.9992 and 0.9984 for the glass and IrO2 pH detectors, respectively) in the gas stream over a wide dynamic range (0.1-100 % CO2 in balance of nitrogen). Moreover, the presented analyzer based on either detector offered several favorable performance characteristics such as reasonably short response and recovery times; excellent signal stability and reproducibility and high selectivity in the presence of non-ionogenic gases, e.g., CH4, N2, O2, CO, etc. The suggested analyzer was applied successfully in the dual-channel monitoring of CO2 absorption from CO2-CH4 binary feed gas mixtures.

Analyzer for continuous monitoring of H2S in gas streams based on a novel thermometric detection

Development, characterization, and application of a novel gas analyzer for continuous monitoring for hydrogen sulfide (H2S) in gas streams are presented. The principle of operation is based on absorbing H2S from the analyte gas stream into aqueous sodium hydroxide solution flowing through a custom-made hollow fiber membrane (HFM) contactor (diffusion scrubber). The stripped sulfide ions in the alkaline solution are oxidized in line with hydrogen peroxide solution. The redox reaction is significantly exothermic and the temperature rise (ΔT) of the flowing mixed reagent stream is measured and proved as useful novel analytical signal for the quantification of H2S. The analyzer exhibited linear response to H2S concentrations for at least two orders of magnitude, i.e., 0.05–5.0% (r2=0.9996). The analyzer exhibited excellent selectivity in the presence of several common gases such as CO2, CO, CH4, O2 and N2 whereas SO2 exerts positive interference (∼22%). The analyzer exhibited excellent signal repeatability (CV<1%), excellent signal stability (2h at least) and acceptable response time (t95%) of 7min. In addition to the favorable performance characteristics, the presented analyzer offers several other advantages such as long operational life time, conveniently tuned sensitivity, low cost of construction and operation; (iv) short setup time, and (v) high reliability. The analyzer was successfully applied in monitoring the removal of H2S from gas stream using a lab scale setup.

A semi-continuous measurement of gaseous ammonia and particulate ammonium concentrations in PM2.5 in the ambient atmosphere

Ammonia has a short residence time in the atmosphere and rapidly neutralizes acid gases that occur near its source, requiring a rapid measurement system for ammonia and particulate ammonium concentrations to better understand their sources, temporal variation of ammonia emissions, and the formation of secondary ammonium aerosols. A semi-continuous measurement system, consisting of a diffusion scrubber, a particle growth chamber, an air-liquid separator, and a fluorescent detector, was developed to determine both gaseous ammonia (NH3) and particulate ammonium (NH4+) in PM2.5 in the ambient atmosphere of Gwangju, South Korea, during the months of March, April, July, and September of 2007. During the sampling periods, the average concentrations of ammonia and ammonium were found to be 2.33 ± 1.29 μg/m3 and 1.89 ± 0.99 μg/m3, respectively. Although the average gaseous ammonia concentration was highest in March, the particulate ammonium concentration was higher during the warmer season, reaching 2.08 ± 1.07 μg/m3 and 2.32 ± 0.94 μg/m3 in April and July, respectively, while only 1.68 ± 0.61 μg/m3 in March and 1.24 ± 0.99 μg/m3 in September. It is proposed that the higher availability of acid species during the warmer months produced a significant amount of particulate ammonium sulfate. Diurnal fluctuation of ammonia and ammonium during the warmer months showed that their peak time occurred at approximately 10:00 am. Both ammonia and ammonium concentrations were better correlated during the warmer months than during the cooler months. Further, the data suggest that the ammonia and ammonium were measured under well dispersed conditions, and multiple sources contributed to the ammonia at the sampling site.

Development of an Automated Diffusion Scrubber-Conductometry System for Measuring Atmospheric Ammonia

A semi-continuous and automated method for quantifying atmospheric ammonia at the parts per billion level has been developed. The instrument consists of a high efficiency diffusion scrubber, an electrolytic on-line anion exchange device, and a conductivity detector. Water soluble gases in sampled air diffuse through the porous membrane and are absorbed in an absorbing solution. Interferences are eliminated by using an anion exchange devises. The electrical conductivity of the solution is measured without chromatographic separation. The collection efficiency was over 99%. Over the 0-200 ppbv concentration range, the calibration was linear with = 0.99. The lower limit of detection was 0.09 ppbv. A parallel analysis of Seoul air over several days using this method and a diffusion scrubber coupled to an ion chromatography system showed acceptable agreement, = 0.940 (n = 686). This method can be applied for ambient air monitoring of ammonia.

Versatile microanalytical system with porous polypropylene capillary membrane for calibration gas generation and trace gaseous pollutants sampling applied to the analysis of formaldehyde, formic acid, acetic acid and ammonia in outdoor air

The analytical determination of atmospheric pollutants still presents challenges due to the low-level concentrations (frequently in the μg m −3 range) and their variations with sampling site and time. In this work, a capillary membrane diffusion scrubber (CMDS) was scaled down to match with capillary electrophoresis (CE), a quick separation technique that requires nothing more than some nanoliters of sample and, when combined with capacitively coupled contactless conductometric detection (C 4D), is particularly favorable for ionic species that do not absorb in the UV–vis region, like the target analytes formaldehyde, formic acid, acetic acid and ammonium. The CMDS was coaxially assembled inside a PTFE tube and fed with acceptor phase (deionized water for species with a high Henry's constant such as formaldehyde and carboxylic acids, or acidic solution for ammonia sampling with equilibrium displacement to the non-volatile ammonium ion) at a low flow rate (8.3 nL s −1), while the sample was aspirated through the annular gap of the concentric tubes at 2.5 mL s −1. A second unit, in all similar to the CMDS, was operated as a capillary membrane diffusion emitter (CMDE), generating a gas flow with know concentrations of ammonia for the evaluation of the CMDS. The fluids of the system were driven with inexpensive aquarium air pumps, and the collected samples were stored in vials cooled by a Peltier element. Complete protocols were developed for the analysis, in air, of NH 3, CH 3COOH, HCOOH and, with a derivatization setup, CH 2O, by associating the CMDS collection with the determination by CE-C 4D. The ammonia concentrations obtained by electrophoresis were checked against the reference spectrophotometric method based on Berthelot's reaction. Sensitivity enhancements of this reference method were achieved by using a modified Berthelot reaction, solenoid micro-pumps for liquid propulsion and a long optical path cell based on a liquid core waveguide (LCW). All techniques and methods of this work are in line with the green analytical chemistry trends.

Variations and sources of ambient formaldehyde for the 2008 Beijing Olympic games

As the host city of the 2008 Olympic games, Beijing implemented a series of air pollution control measures before and during the Olympic games. Ambient formaldehyde (HCHO) concentrations were measured using a fluorometric instrument based on a diffusion scrubber and the Hantzsch reaction; hydrocarbons were simultaneously measured using gas chromatography–mass spectrometry (GC–MS). Meteorological parameters, CO, O 3, and NO 2 concentrations were measured by standard commercial instrumentation. In four separate periods: (a) before the vehicle plate number control (3–19 July); (b) during the Olympic Games (8–24 August); (c) during the Paralympic Games (6–17 September) and (d) after the vehicle control was ceased (21–28 September), the average HCHO mixing ratios were 7.31 ± 2.67 ppbv, 5.54 ± 2.41 ppbv, 8.72 ± 2.48 ppbv, and 6.42 ± 2.79 ppbv, while the total non-methane hydrocarbons (NMHCs) measured were 30.41 ± 18.08 ppbv, 18.12 ± 9.38 ppbv, 30.50 ± 13.37 ppbv, and 33.33 ± 15.85 ppbv, respectively. Both HCHO and NMHC levels were the lowest during the Olympic games, and increased again during the Paralympic games even with the same vehicle control measures operative. Similar diurnal HCHO and O 3 patterns indicated that photo-oxidation of NMHCs may be the major source of HCHO. The diurnal profile of total NMHCs was very similar to that of NO 2 and CO: morning and evening peaks appeared in rush hours, indicating even after strict vehicle control, automobile emission may still be the dominant source of the HCHO precursors. The contributions of HCHO, alkanes, alkenes, and aromatics to OH loss rates were also calculated. HCHO contributed 22 ± 3% to the total VOCs and 24 ± 1% to the total OH loss rate. HCHO was not only important in term of abundance, but also important in chemical reactivity in the air.

Semicontinuous Automated Measurement of Organic Carbon in Atmospheric Aerosol Samples

A fully automated measurement system for ambient aerosol organic carbon, capable of unattended operation over extended periods, is described. Particles are collected in a cyclone with water as the collection medium. The collected sample is periodically aspirated by a syringe pump into a holding loop and then delivered to a wet oxidation reactor (WOR). Acid is added, and the WOR is purged to measure dissolved CO(2) or inorganic carbonates (IC) as evolved CO(2). The IC background can often be small and sufficiently constant to be corrected for, without separate measurement, by a blank subtraction. The organic material is now oxidized stepwise or in one step to CO(2). The one-step oxidation involves UV-persulfate treatment in the presence of ozone. This treatment converts organic carbon (OC) to CO(2), but elemental carbon is not oxidized. The CO(2) is continuously purged from solution and collected by two sequential miniature diffusion scrubbers (DSs), a short DS preceding a longer one. Each DS consists of a LiOH-filled porous hydrophobic membrane tube with terminal stainless steel tubes that function as conductance-sensing electrodes. As CO(2) is collected by the LiOH-filled DSs, hydroxide is converted into carbonate and the resulting decrease in conductivity is monitored. The simultaneous use of the dual short and long DS units bearing different concentrations of LiOH permits both good sensitivity and a large dynamic range. The limit of detection (LOD, S/N = 3) is approximately 140 ng of C. With a typical sampling period of 30 min at a sampling rate of 30 L/min, this corresponds to an LOD of 160 ng/m(3). The approach also provides information on the ease of oxidation of the carbonaceous aerosol and hence the nature of the carbon contained therein. Ambient aerosol organic carbon data are presented.

Determination of Low Molecular Weight Monocarboxylic Acid Gases in the Atmosphere by Parallel Plate Diffusion Scrubber-Ion Chromatography

A method has been developed for the determination of the concentration of low molecular weight monocarboxylic acid gases in the atmosphere. The method involves quantitative collection of analyte gases using a parallel plate diffusion scrubber and subsequent ion analysis by ion chromatography. Among the gases are formic acid, acetic acid, propionic acid, n-butyric acid, and n-valeric acid. Method detection limits are on the order of sub to low parts-per-trillion by volume. The method has been successfully applied to ambient air analysis.

Simultaneous Measurements of Gaseous Nitrous Acid and Particulate Nitrite Using Diffusion Scrubber/Steam Chamber/Luminol Chemiluminescence

An instrument was developed for the simultaneous determination of gas- and aerosol-phase nitrous acid (HONO). Gaseous HONO (HONO(g)) was sampled by a diffusion scrubber and particulate nitrite (NO2 − (p)) was collected by a particle growth chamber. The collected samples were analyzed in time-sharing manner, based on the peroxynitrite-induced luminol chemiluminescence. The automated system was found to be sensitive with 13 pptv of detection limit, fast with 4 min. of sampling frequency, and simple and affordable to construct and operate. The system was optimized by adjusting the experimental parameters. The system was applied to the field measurement of gas- and particle-phase HONO during the springtime of 2004 in Gwangju, South Korea. HONO(g) concentrations varied diurnally from 200 pptv around 3 P.M. to 800 pptv at 5 A.M. The variation of NO2 − (p) was not significant with the maximum of 240 pptv at 11 P.M. and the minimum of 170 pptv at 4 P.M., not displaying distinct characteristics.

Investigation of nitrous acid concentration in an indoor environment using an in-situ monitoring system

An in-situ measurement system for the determination of nitrous acid (HONO) was developed and used at an indoor residential environment. The system uses a diffusion scrubber to sample gaseous HONO and the peroxynitrite-induced luminol chemiluminescent method to quantify the amount of HONO. In this system, the detection limit of HONO, estimated as three times the noise level of the scrubbing solution blank, was 120 pptv for a 2-min integrated sample. Indoor HONO and NO x concentrations were determined for 7 days in the living room of an apartment with a gas range for cooking in the kitchen. Close examination of the relationships among HONO, NO, and NO 2 concentrations during both the background and combustion periods confirm that the observed HONO was formed not only by direct emission from gas combustion, but also from heterogeneous reactions of NO 2 with H 2O on indoor surfaces. The average ratio of HONO to NO 2 over the study period was 0.12 ± 0.05. The HONO/NO 2 concentration ratio was 0.04–0.08 during the combustion period, whereas it was 0.10–0.25 after combustion had stopped. This suggests that HONO was generated through different production processes, both during combustion and after the completion of combustion. The controlled combustion experiments indicate that the burning rate is an important factor to determine the peak HONO concentration. In darkness, HONO had a nearly constant removal rate for all of the combustion experiments, whereas the removal rates of NO and NO 2 depended on the burning rates of the gas range. Combustion experiments conducted at the fixed burning rate setting show also that ventilation decreased HONO concentration. This indicates that the airflow rate of the range hood fan is an important factor to control the concentration of indoor air pollutants.

An automated and semi-continuous method for the analysis of water-soluble constituents in PM 2.5

An automated and semi-continuous method for measuring water-soluble constituents in PM 2.5 was developed. The system consists of a multi-tube diffusion scrubber (MTDS), a low temperature particle impactor (LTPI), an inertial air/liquid separator, and two ion chromatography systems. The MTDS acts as an interfering gas removal system and also as a humidifier for growing particles. Since the MTDS operates at 40 °C, the loss of volatile compounds and hydrological conversion of nitrogen oxides to nitrite were not of significant concern. The condensation of water vapor, dissolution of soluble constituents, and capture of insoluble particles occurred in the LTPI. The condensed liquid containing the dissolved species and the insoluble particles was separated from the airflow using an inertial air/liquid separator. The analysis of cations and anions in the effluent liquid was performed using two ion chromatography systems. The collection efficiency, including the inlet loss, of the system was 96.6 ± 7.1% at an air flow rate of 1.0 SLPM. The limits of detection ranged from 12 to 57 ng/m 3 for major ionic constituents without any pre-concentration procedure. This method was tested in the field and the average data capture was over 90%, demonstrating the reliability of the system.

실시 측정시스템을 활용한 실내 환경에서 HONO 농도 조사

We developed an in-situ analyzer to understand the HONO levels in indoor environments. The in-situ measurement system utilizes a diffusion scrubber and luminol chemiluminescence to measure the HONO concentration with time resolution of 4-minute. Concentrations of NO, <TEX>$NO_{2}$</TEX>, and HONO were determined at an indoor air of an apartment for 9 days using the developed in-situ analyzer. Indoor HONO concentrations were highly elevated when a gas range was operated. Enhancements of the indoor NO, <TEX>$NO_{2}$</TEX>, and HONO concentrations during combustion indicate that the observed indoor HONO was formed by direct emission. In addition to the direct emission, the indoor HONO was partially generated from heterogeneous reactions of <TEX>$NO_{2}$</TEX> on indoor surfaces, which was supported by strong relationships between peak NO, <TEX>$NO_{2}$</TEX>, and HONO concentrations, high HONO/<TEX>$NO_{2}$</TEX> ratio and a weak correlation between NO and HONO concentrations. Additionally, three combustion experiments during the whole measurement period were performed to investigate the effects of unvented and vented gas burning on the HONO, NO, and <TEX>$NO_{2}$</TEX> concentrations and their decay. The decay rate of the HONO concentration was significantly less than the NO and <TEX>$NO_{2}$</TEX> decay rates for all the experiments, indicating that the lifetimes of trace nitrogen species in indoor environment varied in the order approximately HONO><TEX>$NO_{2}$</TEX>>NO.

Field test of four methods for gas-phase ambient nitric acid

Three semi-continuous methods for detecting nitric acid (HNO 3) were tested against the annular denuder + filter pack (ADS) integrated collection technique at the Tampa Bay Regional Atmospheric Chemistry Experiment (BRACE) Sydney research station ∼ 20 km downwind of the Tampa, Florida, urban core. The semi-continuous instruments included: two slightly differing implementations of the NO Y - NO Y * (total oxides of nitrogen minus that total denuded of HNO 3) denuder difference technique, one from the NOAA Air Resources Lab (ARL), and one from Atmospheric Research and Analysis, Inc. (ARA); the parallel plate wet diffusion scrubber + online ion chromatography technique from Texas Tech University (TTU); and the chemical ionization mass spectrometer from the Georgia Institute of Technology (GIT). Twelve hour ADS samples were collected by the University of South Florida (USF). Results for 10 min samples computed from the various higher sampling frequencies of each semi-continuous instrument showed good agreement ( R 2 > 0.7 ) for afternoon periods of the highest production and accumulation of HNO 3. Further, agreement was within ± 30 % for these instruments even at HNO 3 concentrations < 0.30 ppb . The USF ADS results were biased low, however, by 44%, on average, compared to the corporate 12 h aggregated means from the semi-continuous methods, and by > 60 % for the nighttime samples; ADS results were below the corporate mean maximum HNO 3 concentration by > 30 % as well. The four instruments using semi-continuous methods, by contrast, were all within 10% of each other's 12 h mean mixing ratios. While only ARA employed a formal minimum detection limit at 0.050 ppb, error analysis with the other techniques established that at the same level of precision, TTU's effective limit was approximately the same as ARA's and that ARL's limit was 0.030 ppb; analysis for GIT showed no apparent effective limit at the levels of HNO 3 encountered in this field study. The importance of sample inlet height for HNO 3 measurements was indirectly shown through comparison to previous field work at this site when sample inlet heights ranged from 1.5–10 m and produced systematic discrepancies in HNO 3 concentrations correlated with height of more than a factor of 2.

Measurement of Ammonia in Human Breath with a Liquid-Film Conductivity Sensor

Measurement of breath NH3 is of interest in clinical applications as it can be used as a measure of kidney/liver functions as well as halitosis. We have developed a liquid-film conductivity sensor to measure NH3 in human breath. A film of dilute H2SO4 is formed on the top of two metal capillary tubes placed in a concentric annular arrangement. The tube exterior has been specially treated to render it hydrophilic. As breath passes over the sensor tip, the film collects NH3 and the solution conductivity (measured by the concentric capillaries functioning as electrodes) decreases accordingly. This initial rate of conductivity decrease was determined to be the best metric (most rapid and least dependent on breath pCO2) for ammonia, relative to time to attain complete neutralization (conductivity minimum) or the final rate of conductivity increase as more ammonia dissolves after neutralization. The absorbing solution composition was optimized so that CO2 does not interfere. Both dynamic measurement using mask sampling and offline balloon sampling were performed. Ammonia readily absorbs on surfaces when significant concentrations of water vapor are present. As such, memory effects are common when analyzing human breath for ammonia. This problem was successfully eliminated. The results from this sensor agreed well with data obtained by a solution-phase fluorometric technique using a porous membrane diffusion scrubber and o-phthalaldehyde derivatization chemistry. For breath CO2 measurement, the applicability of a similar sensor that relies on a NaOH film was also demonstrated.

Sequential multiple analyses of atmospheric nitrous acid and nitrogen oxides

Sequential injection analysis (SIA) was applied to multi-gas monitoring for atmospheric analysis. HONO, NO 2 or NO was collected in an individual diffusion scrubber in which the channel array was filled with either HCl or triethanolamine solution. All analytes were collected in the form of nitrite ions in the scrubber, and were transferred via a 12-port selection valve into a 2.5-ml syringe. The reagent, 3-amino-1,5-naphthalenedisulfonic acid (C-acid) solution was subsequently introduced into the syringe, and inter-mixed with the nitrite sample, whereafter the mixed solution was transferred to a heated reactor and held for 3 min at 100 °C. After that, the sample/reagent solution was returned to the syringe and alkalinized. Then, the final solution was analyzed using a homemade fluorescence detector. Atmospheric HONO, NO 2 and NO were successfully monitored 3 or 4 times/h. The limits of detection were 0.22, 0.28 and 0.35 ppbv for HONO, NO 2 and NO, respectively. It was demonstrated for the first time that SIA is a good tool for multi-gas atmospheric analysis. These nitrogen–oxygen compounds are interconvertible, and the simultaneous measurement of these gases is important. Especially, HONO is a source of OH radicals which contribute greatly to atmospheric pollution, and indeed atmospheric chemistry. This method allows the three gases to be measured using one system. The NO 2 and NO data obtained by SIA was compared with those obtained using chemiluminescence instrument. SIA has been successfully applied to atmospheric measurements. Interestingly, it was observed that HONO levels rose toward the end of periods of rain.