SO2 Gas Concentration Research Articles

DETECTION OF HAZARDOUS SO2 BY MWCNTS-BASED GAS SENSORS A NEW APPLICATION FOR MONITORING IN MUSEUMS

This study aims to investigate advance material and develops a technique that detects the smallest traces of hazard gases for the instantaneous rate of atmospheric corrosion of archaeological materials indoor and outdoor. This article describes the advance and use of multiple-walled carbon nanotubes (MWCNT) with carbon nanoparticles and spheres as a network to investigate it as resistive gas nanosensors for SO2 detection. The responses of the sensors based on the MWCNs in various concentration to SO2 responses, in SO2 ambient air, performed by resistance measurements from room temperatures of 25 °C to 250 °C, more than 400 °C the structure will. SO2 gas concentration from 0.5 to 20 ppm to find new application, particularly application in Museums to conserve cultural heritage materials from deterioration caused by hazard gases.

Surface lanthanide activator doping for constructing highly efficient energy transfer-based nanoprobes for the on-site monitoring of atmospheric sulfur dioxide.

The sensitive and on-site detection of sulfur dioxide (SO2) is in great demand in the fields of food safety and environmental protection. Here, we developed a novel upconversion nanoprobe based on the luminescence energy transfer mechanism for monitoring the atmospheric SO2 concentrations. The lanthanide emitters, Tm3+ ions, were optimized to be doped on the surface layer of the upconversion nanoparticles to improve their energy transfer efficiency by minimizing the distance between the emitters and the surface quencher, a cyanine dye. As a proof-of-concept, the optimal nanoprobe was utilized to detect SO2 water derivatives, bisulfite ions, exhibiting a linear luminescence increase in the range of 1 nM to 10 nM. Furthermore, we assembled the cyanine-modified upconversion nanoparticles onto a test paper, and used a smartphone-based detection platform to achieve portable and visual detection of SO2. The test paper showed a strong luminescence stability, homogeneity and good anti-interference. The limit of detection for SO2 gas was found to be 1 ng L-1. This novel upconversion test paper was also demonstrated to directly monitor the concentration of SO2 gas in atmosphere.

Development of an Optical Multispectral Remote Sensing System for Measuring Volcanic Surface Phenomena – Promotion Project for Next Generation Volcano Research B2 (Subtopic 2-2)

In 2016, we launched the “Promotion Project for Next Generation Volcano Research B2 (Theme B: Development of Cutting-edge Volcano Observation Technology, subtheme 2: Development of Remote Sensing Techniques for Volcano Observation), subtopic 2-2 (Development of Remote Sensing Techniques for Surface Phenomena of Volcano)” under the “Integrated Program for Next Generation Volcano Research and Human Resources Development” [1], aiming at the development of an optical multispectral remote sensing system for measuring volcanic surface phenomena. With subtopic 2-2, we are planning to develop a new observation device called a surface phenomena imaging camera (SPIC), which is technically superior to current remote sensing techniques, i.e., optical remote observation techniques used to observe volcanic surface phenomena from aircrafts or ground. We are also aiming at applying the developed observation system to quantify volcanic activities and determine volcanic eruption potentials (degrees of urgency) or branching of event trees for volcanic crises with high accuracy, contributing to better predictions of volcanic eruption transitions. To achieve the above-mentioned aims, we started the development of the SPIC by equipping it with camera-type sensors, based on preliminary analyses of the experimental observations made with the airborne spectral imaging system ARTS-SE, which consists of a pushbroom scanner and a camera system, developed by the National Research Institute for Earth Science and Disaster Resilience in FY 2015. We have already developed its components, such as the prototype filter-type multiband cameras SPIC-UC, a prototype uncooled infrared camera, SPIC-C, a cooled camera, and SPIC-SS, a visible-light camera. The SPIC-UC is a two-band camera with the function of visualizing temperature and SO2 gas concentration distributions. The SPIC-C has the function of measuring temperatures between 2 and 1075◦C with high accuracy (noise equivalent temperature difference, NETD: 16 mK); it is equipped with a sensor and a filter wheel that work in the middle wave infrared region (MWIR). The SPIC-SS is a six-lens multiband camera system that estimates the measured images from multiband spectra (6 bands) to hyper spectra (300 bands). Further, we studied a method to estimate digital surface model with a ∼30-m error. As our plan has progressed as scheduled, we intend to complete the prototype SPIC by 2020.

High sensitive and low-concentration sulfur dioxide (SO2) gas sensor application of heterostructure NiO-ZnO nanodisks

This paper reports the synthesis and characterization of NiO-ZnO nanodisks synthesized through a facile hydrothermal method. The morphological characterizations confirmed the formation of well-defined nanodisks in high density with an average thickness of 60 ± 5 nm. The x-ray diffraction analysis confirmed the well incorporation of the NiO into the matrix of ZnO crystal and the average crystallite size for the NiO-ZnO nanodisks was found to be 39.71 nm. The compositional analysis revealed the formation of pure NiO-ZnO nanostructures. The synthesized NiO-ZnO nanodisks were used as electrode materials to fabricate Sulfur dioxide (SO2) gas sensors and the gas sensor response and recovery times were systematically analyzed with respect to the operating temperatures and the SO2 gas concentration. The observed sensor gas response, response time and recovery time of the fabricated NiO-ZnO nanodisks based gas sensor were 16.25, 52 s and 41 s, respectively, towards 20 ppm SO2 gas at an optimized temperature of 240 °C. Thus, it is believed that the NiO-ZnO nanodisks could be a promising candidate for the fabrication of efficient gas sensors towards toxic and hazardous gases.

Applications of quantitative thermal infrared hyperspectral imaging (8–14 μm): measuring volcanic SO2 mass flux and determining plume transport velocity using a single sensor

Remote measurements of sulfur dioxide (SO2) path-concentration and emission rate (mass flux), released by passive volcanic degassing, are a key diagnostic of volcanic behavior. SO2 gas concentrations are also important for public health. Despite the significance of measuring SO2 mass flux at active volcanoes, an accurate method is still very difficult to obtain due largely to uncertainties of plume transport velocities and radiative transfer calculations. Here, we present a new infrared imaging method for deriving SO2 flux at active volcanoes with less than 20% plume transport velocity and radiative transfer uncertainties. The thermal hyperspectral imager (THI) was used for this study. THI is an uncooled remote sensing long-wave thermal infrared (TIR) imaging hyperspectral sensor that can obtain ~ 50 wavelength samples between 8 and 14 μm. Measurements of SO2 at the summit of Kīlauea volcano, collected using THI, are presented, where we obtained (for the periods of July 24–26, 2017, and February 5–6, 2018) a SO2 flux raging between 0 and 20 kg/s with occasional peaks higher than 40 kg/s. The spatial distribution of SO2 path-concentrations was obtained from the THI images by processing them using a newly developed SO2 retrieval algorithm, the SO2 amenable lookup table algorithm (SO2-ALTA). The sampling rate (30 Hz) of the microbolometer camera within THI means raw frames can be used for wind velocity derivation. Volcanic plume motion can be thus inferred by tracking plume features in sequential frames using spatial correlation techniques and knowing the camera angular orientation. Volcanic SO2 flux was estimated from the spatial distribution of SO2 and wind velocity. We evaluated temporal trends of the SO2 flux during the day and the night at the summit of Kīlauea volcano under both clear sky weather with northeasterly trade winds and cloudy sky conditions with low variable wind. These tests showed that the camera and techniques described in this paper provide an effective tool for monitoring SO2 fluxes remotely with less than 20% plume transport velocity and radiative transfer uncertainties and under a variety of background conditions (clear and cloudy sky, cold and hot backgrounds).

Influence of Flue Gas Injection on the Long-Term Durability of a Natural Draft Concrete Cooling Tower.

The article undertakes the very important topic of the long-term durability of concrete in a natural draft concrete cooling tower with flue gas injection. The corrosive conditions, including temperature, relative humidity, and CO2 and SO2 gas concentrations, near the inner wall of a cooling tower with flue gas injection were monitored in real time to obtain the long-term durability performance of concrete. The pH and chemical compositions of the condensed liquid that adhered to the tower’s inner face and the macromorphology, compressive strength, and neutralization depth of in situ specimens were tested periodically. In addition, a finite element numerical simulation was conducted to simulate and verify the concentration distributions of CO2 and SO2 in the flue gas in the cooling tower. The results showed that the cleaned flue gas was enveloped, diluted, and uplifted by hot vapor in the cooling tower, and its concentration decreased. Meanwhile, the effective diffusion radius increased gradually as the flue gas rose. With the same elevation in the cooling tower, the concentration of flue gas decreased rapidly from the central point to the surrounding area. The air near the inner surface of the cooling tower was merely dampened air with a low concentration of acidic gas due to the gigantic diameter of the cooling tower. As a result, the injection of cleaned flue gas will not evidently increase the corrosion risk in a natural draft concrete cooling tower.

MODELING DISPERSI EMISI BAU GAS SO2 DARI CEROBONG INDUSTRI TEKSTIL

Textile Industry gives economic and fi nancial contribution to society, however it has negative impact to the environment, i.e. air pollution, bad smell and noise. For that reason, a study to evaluate exhaust gas emission of some industry textile was carried out from the stack. The aim of the study is to abtain SO2 gas concentration, which is emited from the stack A gas dispersion anlysis, it was indicated that SO2 gas concentration from the stack is still below the standard (1200 mg/m3). Thehighest SO2 concentration was 18 mg/m3 at about 200 meter away from the stack. It meant that SO2 concentration and SO2 odor from the textile industry did not give any impact to the environmentKey words: emission, textile industry,

A comparative study of RGO-SnO2 and MWCNT-SnO2 nanocomposites based SO2 gas sensors

An attempt has been made in the present work to develop a hybrid nanocomposite sensor by exploiting the novel properties of Tin oxide (SnO2), MWCNTs (Carbon nanotubes) and reduced graphene oxide (RGO) for the efficient detection of SO2 gas. MWCNT-SnO2 and RGO-SnO2 hybrid nanocomposite sensors have been prepared by incorporating MWCNTs and RGO into SnO2 nanoparticle colloidal solution respectively by chemical route. Low sensing response of 1.2 is obtained for bare SnO2 sensor at 220°C towards 500ppm SO2 gas. However, enhanced sensing response of ∼22 has been observed for the RGO-SnO2 sensor compared to ∼5 obtained for MWCNT-SnO2 sensor at a lower operating temperature of 60°C towards the same concentration of SO2 gas. Modulation of space charge region at the interface of n-SnO2 and p-RGO on interaction with the target SO2 gas is responsible for the enhanced response.

Synthesis and characterization, electrical and gas sensing properties of N,N′-bis(salicylidene)-1,2-phenylendiamine substituted novel mono and ball-type metallo phthalocyanines

The synthesis of 2,2′-{benzene-1,2-diylbis[nitrilo(E)methylidene]}phenol phenoxy phthalonitrile 1 and 2,2′-{benzene-1,2-diylbis[nitrilo(E)methylidene]}diphenoxy diphthalonitrile 2 were achieved starting from N,N′-bis(salicylidene)-1,2-phenylenediamine, 4-nitrophthalonitrile and anhydrous K2CO3 in DMF at 70°C under argon atmosphere. The template reaction of 1 with the corresponding metal salt gave the mono-nuclear zincphthalocyanine 3. The ball-type metallophthalocyanines 4 and 5 (Zn2Pc2 and LuPc2) were synthesized by starting from compound 2 with the corresponding metal salts heating in the medium without solvent. The compounds were characterized by elemental analysis, FT-IR, UV–Vis, MALDI-TOF mass and 1H NMR spectroscopy techniques. Thin films of the compounds have been deposited by spin coating method on the glass substrate fitted with interdigitated gold electrodes. Electrical response of the films has been investigated by exposing the samples to various concentrations of SO2 gas. While exposure to SO2 has no influence on the electrical conductivity of compound 3, the conductivity of the films of 4 and 5 and strongly depend on the presence of this gas. Completely reversible sensor signals were obtained for these compounds with response and recovery times shorter than 2min. and 40s, respectively.

Sulfur dioxide gas sensor based on Zr4+ and O2− ion conducting solid electrolytes with lanthanum oxysulfate as an auxiliary sensing electrode

A solid electrolyte type SO2 gas sensor based on tetravalent Zr4+ ion conducting Zr39/40TaP2.9W0.1O12 and O2− ion conducting (ZrO2)0.92(Y2O3)0.08 solid electrolytes with 0.7La2O2SO4–0.3(0.8Li2SO4 + 0.2K2SO4) as an auxiliary sensing electrode was developed. The present sensor exhibited a continuous, reproducible, and quantitative response for SO2 gas, and the relationship between the sensor EMF output and the logarithm of the SO2 gas concentration obeyed the Nernst equation at temperatures as low as 480 °C over 80 days. Thus, it is expected to be a good candidate as a practical SO2 gas sensor for on site measurements.

Multi-criteria Analysis of Air Pollution with SO(2) and PM(10) in Urban Area Around the Copper Smelter in Bor, Serbia.

This work presents the results of 4 years long monitoring of concentrations of SO2 gas and PM10 in the urban area around the copper smelter in Bor. The contents of heavy metals Pb, Cd, Cu, Ni, and As in PM10 were determined and obtained values were compared to the limit values provided in EU Directives. Manifold excess concentrations of all the components in the atmosphere of the urban area of the townsite Bor were registered. Through application of a multi-criteria analysis by using PROMETHEE/GAIA method, the zones were ranked according to the level of pollution.

Impact of krypton-85 beta radiation on aerosol particle formation and transformation

In this study the effect of the air ionization by 85 Kr beta radiation on the new particle formation and evolution of aerosol particle size distribution in the experimental chamber was investigated. During the experiments the interaction between air ionization and gas-to-particle conversion processes was distinctly observed. Results showed that the amplitude of the ionic current was dependent both on the chemical impurity concentration and the ionization source activity. Calculated values of parameters (growth and formation rates) of the particle nucleation process were larger when in the experimental chamber concentrations of SO2 and 85 Kr were higher. The growth rate values (42.1 and 45.3 nm=h) were by one order of magnitude higher than the environmental ones (1.2n9.9 nm=h at the Preila station, Lithuania). Experimental data showed that after injection of high SO2 and 85 Kr concentrations in the chamber during the 20 min interval nanometre-size particles created by nucleation were produced in large amounts. Thus, a larger amount of SO2 signicantly inuenced the formation of new particles. During the rst 5 min the concentration of 10 nm particles increased by 3 orders of magnitude with the formation rate of 7.47 cm i3 s i1 . The formation rate of 0.06 cm i3 s i1 in the experiment with the average ambient SO2 concentration (2n3 „g=m 3 ) was analogous to the environmental one (0.14 cm i3 s i1 ). The coagulation sink (CoagS 1;2;3 ) was higher in the experiment with the ambient SO2 concentration and resulted in the lower concentration of particles. The smaller values of the coagulation sink at the higher concentration of SO2 gas have shown that these nano-particles in the air could persist for a longer time, probably in a stable size due to the ion charge.

Removal of SO2 from Industrial Effluents by a Novel Twin Fluid Air-Assist Atomized Spray Scrubber

Wet scrubbers are employed in process industries for scrubbing both gases and particulates. To achieve a high efficiency for scrubbers and meet pollution control standards, industries need a new type of scrubber. In this paper an attempt has been made to design a new spray scrubber by a twin fluid air-assisted atomizer for the removal of SO2. Experimental results for scrubbing of lean sulfur dioxide gas by a novel spray tower using a twin fluid air-assisted atomizer have been presented. The efficiency of the spray column was found to increase with increase in spray liquid flow rate (8.35 × 10−6−33.34 × 10−6 m3/s) and concentration of SO2 gas (400−1200 ppm). A maximum of almost 99.99% efficiency was observed for 1200 ppm at 3.354 × 10−3 m3/s gas flow rate and 33.34 × 10−6 m3/s spray liquid flow rate.

Health risk analysis of volcanic SO2 hazard on Vulcano Island (Italy)

Since the last eruption of the Fossa crater in 1888–1890, intense volcanic degassing has been remaining on Vulcano Island of Sicily (Italy). Toxic sulfur dioxide (SO2) of the solfataric action in this area represents, when inhaled, a permanent natural hazard harming humans. Approximately 500 permanent residents live and 15,000 tourists visit during the summer time the Porto village in the North of Vulcano Island. A cross-disciplinary fuzzy logic risk assessment has been conducted to evaluate health risks of human individuals exposed to higher SO2-concentrations C over certain exposure times t. The simple approach, based on fuzzy set theory, explains health risks semantically by words rather than by numbers. Advantages of this approach are, first, experts, non-experts, decision makers, or the public are able to understand and communicate risk degrees by words without using numbers. Second, in comparison to other risk definitions, the risk is not equal to the vulnerability; it is based on the hazard (SO2-gas clouds) and vulnerability (health effects) in combination. Third, risk levels can be still estimated even when limited or no statistical information is available, e.g., high SO2-concentrations or long exposure times. Moreover, human health risks were determined for C−t-scenarios based on threshold values of the European Union and the World Health Organization. Independently, two additional methods were used to determine the proportions of the population who are exposed to levels of SO2 at which health effects may be expected and also safety zones for civil protection around the degassing fields. In conclusion, SO2-gas concentrations in many parts of Vulcano Island go beyond the proclaimed alert threshold of the European Union and the World Health Organization. For example, the results show that sensitive individuals, such as asthmatics, young children, or elderly people, should not be exposed at any time to the degassing areas in Porto di Levante and at the NE-rim of the Fossa crater. In contrast, healthy non-sensitive individuals should be exposed less than 10 min to the SO2-clouds at these degassing areas, while hiking on the crater rim.

火山ガスと防災

A large amount of SO2 gas was discharged from Miyakejima volcano since the end of September, 2000. The averaged SO2 flux was about 50,000 ton/day in 2000. About 4,000 people could not returned to the island, because SO2 gas has been discharged, and more than 5 ppm of SO2 gas concentrations has been observed frequently around the island. In generally, volcanic gas contains mainly water vapor. The dry gas is largely composed of HF, HCl, SO2 , H2S and CO2 with small amount of N2, H2, He, Ar, CH4 and CO. HF, HCl, SO2 and H2S gases have high toxicity. The volcanic gas disaster occupied about 2.5% of volcanic disaster based on the dead since 1900. In Japan, disasters by volcanic gas occurred 28 times around eleven active volcanoes and 49 people were died during the recent 50 years. Occurrence of volcanic gas disaster is mainly dominated by the configuration of ground around fumarolic area and meterological conditions such as windless, cloudy, foggy weather and formation of inversion layer. SO2 has been released at Oyama volcano in Miyakejima island for more than two years, and the inhabitants had to leave the island. Volcanic gas disaster is influenced by meteorological conditions and local geology. In case of big eruption, volcanic gas ascends to the stratospheric, and aerosol causes low temperature in the world. To reduce the disaster of volcanic gas, it is needed to monitor with a selective gas sensor and to alarm people the forecasted dangers.

二酸化硫黄ガス雰囲気中における イオンマイグレーションの加速とそのメカニズム

The purpose of study is to clarify 1) the acceleration effect of SO2 gas on the generation of migration, and 2) the generation mechanism of migration under the SO2 gas environment. The experiments were carried out using the circuit board set in the cycle testing tank controlling temperature and humidity. The voltage applied to the test wirings was 50 V. SO2 gas concentrations were 0, 0.3, 12 and 85 ppm. Distances between wirings were 0.16, 0.4, 1, 2.5 and 6.3 mm. The one cycle of the cycle testing was first (5°C, 60%RH, 20 min.) and second (25°C, 90%RH, 20 min.). The results show that the progress of the migration in SO2 gas environment is accelerated by changing the water absorbed on the surface between wirings into acid water caused by SO2 gas and migration with wirings of 6.3 mm distance was observed.

Measurement of acidic gas by Annular Denuder System (ADS) in Sha‐Lu, Taiwan

During June 1999 to January 2000, the concentrations of acidic gas were measured by ADS (annular denuder system) in central Taiwan, Taichung. The concentration of HNO2, HNO3, SO2, NH3and HCl were 2.81, 1.63, 24.69, 15.75 and 1.08 μg/m3, respectively. For the seasonal variations of acidic gases, the average SO2and NH3concentrations were higher in summer, and lower in winter. Contrarily, the HNO2and HNO3concentration were lower in summer, and higher in winter. Four meteorological factors: wind speed (m/s), wind direction, temperature (°C) and relative humidity (%) were taken into account in this study. Concentrations (μg/m3) of SO2and NH3were moderate positive related to temperature (°C) with R2 value of 0.668 and 0.678, respectively. The highest value of average SO2gas concentrations appeared in the SSW direction. It meant that the Taichung thermal power station which located in the west side of the sampling site were not the largest SO2contributor to the sampling area. The factories surrounded in the directions of southern‐west and south could be the major SO2contributor for Sha‐Lu area.

Substance P content and preprotachykinin gene-I mRNA expression in a rat model of chronic bronchitis.

Chronic exposure of rats to high concentrations of SO2 gas induces a syndrome similar to human chronic bronchitis. The aim of these studies was to determine if substance P (SP) content in the trachea or lungs was elevated in this animal model of chronic bronchitis, and whether an increase in SP content was associated with an increase in preprotachykinin gene-I (PPT) mRNA expression. Rats were exposed to air (controls) or 250 ppm SO2 gas, 5 h per day, 5 days per week, for a period of 4 wk. Animals were killed and the lungs and trachea were frozen in liquid nitrogen for measurement of SP content by enzyme-linked immunosorbent assay. The SP content of the tracheas from SO2-exposed rats was 3-fold greater than controls (8.9 +/- 1.2 and 3.0 +/- 0.7 pmol/g tissue, respectively; P=0.0005), whereas the SP content of the lungs was not different (SO2 = 4.8 +/- 0.8 and air = 3.0 +/- 0.7 pmol/g tissue, respectively; P = 0.06). In order to determine whether SP synthesis in the cell bodies of the C-fibers innervating the trachea and lungs accompanied a change in SP levels, thoracic dorsal root ganglia and nodose ganglia were removed and PPT mRNA quantitated by Northern analysis. There was no difference in PPT mRNA between control and SO2-exposed rats in nodose or dorsal root ganglia. These results suggest a post-transcriptional mechanism of PPT regulation. Elevated SP levels could play a protective role in the responses of the airways to chronic exposure of inhaled irritants.

Large‐scale volcanic activity at Maat Mons: Can this explain fluctuations in atmospheric chemistry observed by Pioneer Venus?

Magellan (and Pioneer Venus Orbiter (PVO)) found high mountain terrains on Venus (∼2.5 km above 6051 km planetary radius) exhibit anomalously low radiothermal emissivity. This is thought to result from weathering of primary Venus rock, which at high altitudes produces a distinctive high‐dielectric‐constant mineral assemblage. Deviations from the nominal altitude‐emissivity pattern have been used as a crude chronometric tool with which to date Venusian landforms. This technique indicates Maat Mons (an unusually large shield volcano, standing 9.17 km above 6051 km planetary radius, at 2.1°N, 194.3°E) has undergone a “recent” episode of large‐scale volcanic activity; a deduction also implied morphologically. The present paper investigates whether a plinian eruption at Maat Mons could explain the enhanced concentrations of SO2 gas in the upper atmosphere of Venus that were detected by the Pioneer Venus UV spectrometer. The results show for a minimum vent radius of 156 m, a minimum eruption temperature of 1200 K, and a magmatic volatile content of ∼5 wt%, a plinian eruption at the summit of Maat Mons can explain the anomalous concentration of SO2 gas. This would mean Maat Mons is an active volcano.

Increased airway responsiveness to inhaled methacholine in a rat model of chronic bronchitis.

Chronic exposure of rats to high concentrations of SO2 gas causes pathologic changes in airway similar to those seen in human chronic bronchitis. The purpose of this study was to examine the pulmonary mechanical correlates of these changes and to quantify the extent of mucous hypersecretion by measuring changes in mucous glycoproteins. Female Sprague-Dawley rats were exposed to 250 ppm SO2 gas, 5 h/d, 5 d/wk, for a period of 4 wk. Control rats were exposed to air only. On the day after the last SO2 exposure, rats were anesthetized, instrumented for the measurement of pulmonary resistance (RL) and dynamic compliance (Cdyn), and ventilated. Chronic SO2 exposure caused a small but significant increase in RL and decrease in Cdyn. Airway responsiveness to inhaled aerosolized methacholine was increased in SO2-exposed rats, as indicated by approximately 6.6- and 4.6-fold decreases respectively, in the doses of inhaled methacholine required to double RL or decrease Cdyn to 50% of baseline. SO2 exposure had no effect on the contractile response of the trachea measured in vitro. Tracheae and lungs from SO2-exposed animals exhibited 140 and 535% increases in measured neutral mucous glycoproteins, respectively, and 33 and 37% increases in acid glycoproteins. Our results indicate that this animal model of chronic bronchitis mimics the mucous hypersecretion, airway obstruction, and increased airway responsiveness observed in human bronchitis and may allow us to begin to probe their mechanistic basis.