Nanoparticle-coated micro-optofluidic ring resonator as a detector for microscale gas chromatographic vapor analysis.

A vapor sensor comprising a nanoparticle-coated microfabricated optofluidic ring resonator (µOFRR) is introduced. A multilayer film of polyether functionalized, thiolate-monolayer-protected gold nanoparticles (MPN) was solvent cast on the inner wall of the hollow cylindrical SiOxµOFRR resonator structure, and whispering gallery mode (WGM) resonances were generated with a 1550 nm tunable laser via an optical fiber taper. Reversible shifts in the WGM resonant wavelength upon vapor exposure were detected with a photodetector. The µOFRR chip was connected to a pair of upstream etched-Si chips containing PDMS-coated separation µcolumns and calibration curves were generated from the peak-area responses to five volatile organic compounds (VOCs). Calibration curves were linear, and the sensitivities reflected the influence of analyte volatility and analyte-MPN functional group affinity. Sorption-induced changes in film thickness apparently dominate over changes in the refractive index of the film as the determinant of responses for all VOCs. Peaks from the MPN-coated µOFRR were just 20-50% wider than those from a flame ionization detector for similar µcolumn separation conditions, reflecting the rapid response of the sensor for VOCs. The five VOCs were baseline separated in <1.67 min, with detection limits as low as 38 ng.

A nanoparticle-coated chemiresistor array as a microscale gas chromatograph detector for explosive marker compounds: flow rate and temperature effects.

The effects of flow rate and temperature on the performance of a microscale gas chromatographic (µGC) detector consisting of a chemiresistor (CR) array coated with different thiolate-monolayer-protected gold nanoparticles (MPNs) are described with respect to the analysis of three gas-phase markers of the explosive trinitrotoluene (TNT): 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), and 2,3-dimethyl-2,3-dinitrobutane (DMNB). In chamber tests, sensors were stable at 70 °C for several days in air, with <2% sensitivity drift per day and virtually no change in the array response patterns. In tests with a conventional upstream GC column, increasing the array temperature from 55-80 °C (1.2 mL min(-1)) led to similar (i.e., 4-6.6-fold) decreases in sensitivity, increases in the limits of detection (LODs), and increases in (estimated) chromatographic resolution. Increasing the flow rate from 1.1-3.7 mL min(-1) (70 °C) led to ∼1.3-2-fold decreases in sensitivity and LOD for 2,4-DNT and 2,6-DNT, a ∼2-fold net increase in LOD for DMNB (passes through a maximum), and a <2-fold increase in resolution. Results indicate that the rates of desorption of the marker vapors out of the MPN films are important determinants of observed trends. With Si-micromachined focuser/injector and separation column devices placed upstream of a CR array held at 70 °C, a mixture of the two primary markers, 2,4-DNT and DMNB, and four similarly volatile alkane interferents was separated in 1.5 min at 3 mL min(-1).

Organic vapor discrimination with chemiresistor arrays of temperature modulated tin-oxide nanowires and thiolate-monolayer-protected gold nanoparticles.

This paper explores the discrimination of organic vapors with arrays of chemiresistors (CRs) employing interface layers of tin-oxide nanowires (NWs) and thiolate-monolayer-protected gold nanoparticles (MPNs). The former devices use contact-printed mats of NWs on micro-hotplate membranes to bridge a pair of metal electrodes. Oxidation at the NW surface causes changes in charge transport, the temperature dependence of which differs among different vapors, permitting vapor discrimination. The latter devices use solvent cast films of MPNs on interdigital electrodes operated at room temperature. Sorption into the organic monolayers causes changes in film tunneling resistance that differ among different vapors and MPN structures, permitting vapor discrimination. Here, we compare the performance and assess the 'complementarity' of these two types of sensors. Calibrated responses from an NW CR operated at two different temperatures and from a set of four different MPN CRs were generated for three test vapors: n-hexane, toluene, and nitromethane. This pooled data set was then analyzed using principal components regression classification models with varying degrees of random error superimposed on the responses via Monte Carlo simulation in order to estimate the rates of recognition/discrimination for arrays comprising different combinations of sensors. Results indicate that the diversity of most of the dual MPN-CR arrays exceeds that of the dual NW-CR array. Additionally, in assessing all possible arrays of 4-6 CR sensors, the recognition rates of the hybrid arrays (i.e. MPN + NW) were no better than that of the 4-sensor array containing only MPN CRs.

Densely integrated array of chemiresistor vapor sensors with electron-beam patterned monolayer-protected gold nanoparticle interface films.

Use of electron-beam induced crosslinking to pattern films of monolayer-protected gold nanoparticles (MPNs) onto a chemiresistor (CR) sensor array is described. Each of the four CRs comprises a 100 µm(2) set of interdigital electrodes (IDEs) with 100 nm widths and spaces, separated from adjacent devices by 4 µm. Films of four MPNs, each with a different thiolate monolayer, were successively patterned on the IDEs. Vapor exposures yield rapid, reversible changes in CR resistances and differential vapor sensitivities comparable to those reported for larger CRs with unpatterned MPN films. The array response patterns facilitate vapor discrimination. This is the smallest MPN-coated CR array yet reported. The advantages of using such an array as the detector in microfabricated gas chromatographic analyzers are considered.

CMOS Baseline Tracking and Cancellation Instrumentation for Nanoparticle-Coated Chemiresistors.

Chemiresistor (CR) sensors and sensor arrays coated with thiolate-monolayer-protected gold nanoparticle (MPN) interfaces show great promise as detectors in gas-chromatographic microsystems with applications in biomedical and environmental analysis including breath biomarkers of disease. This paper describes a new readout circuit that overcomes the wide range of baseline resistances and drift in baseline values inherent to MPN-coated CRs to achieve a 57 ppm readout resolution. The 0.5-mum CMOS circuit operates at 5 V and provides a response resolution of 74 muV. It can cancel baseline voltages from 0.3 to 4.3 V with an accuracy of 4.2 mV and can track and compensate for drifts up to 30 mV/min. Performance was verified with MPN-coated CRs, where drift was measured and effectively cancelled. The circuit topology and size support an on-chip MPN-coated CR sensor array.

Analysis of solvent vapors in breath and ambient air with a surface acoustic wave sensor array.

This article describes the development and evaluation of a small prototype instrument employing an array of four polymer-coated surface acoustic wave (SAW) sensors for rapid analysis of organic solvent vapors in exhaled breath and ambient air. A thermally desorbed adsorbent preconcentrator within the instrument is used to increase sensitivity and compensate for background water vapor. Calibrations were performed for breath and dry nitrogen samples in Tedlar bags spiked with 16 individual solvents and selected binary mixtures. Responses were linear over the 50- to 400-fold concentration ranges examined and mixture responses were additive. The resulting library of vapor calibration response patterns was used with extended disjoint principal components regression and a probabilistic artificial neural network to develop vapor-recognition algorithms. In a subsequent analysis of an independent data set all individual vapors and most binary mixture components were correctly identified and were quantified to within 25% of their actual concentrations. Limits of detection for a 0.25 l. sample collected over a 2.5-min period were <0.3xTLV for 14 of the 16 vapors based on the criterion that all four sensors show a detectable response. Results demonstrate the feasibility of this technology for workplace analysis of breath and ambient air.

A portable, high-speed, vacuum-outlet GC vapor analyzer employing air as carrier gas and surface acoustic wave detection.

Vacuum-outlet GC with atmospheric-pressure air as the carrier gas is implemented at outlet pressures up to 0.8 atm using a low-dead-volume polymer-coated surface acoustic wave (SAW) detector. Increases in the system outlet pressure from 0.1 to 0.8 atm lead to proportional increases in detector sensitivity and significant increases in column efficiency. The latter effect arises from the fact that optimal carrier gas velocities are lower in air than in more conventional carrier gases such as helium or hydrogen due to the smaller binary diffusion coefficients of vapors in air. A 12-m-long, 0.25-mm-i.d. tandem column ensemble consisting of 4.5-m dimethyl polysiloxane and 7.5-m trifluoropropylmethyl polysiloxane operated at an outlet pressure of 0.5 atm provides up to 4 x 10(4) theoretical plates and a peak capacity of 65 (resolution, 1.5) for a 3-min isothermal analysis. At 30 degrees C, mixtures of vapors ranging in vapor pressure from 8.6 to 76 Torr are separated in this time frame. The SAW detector cell has an internal volume of < 2 microL, which allows the use of higher column outlet pressures with minimal dead time. The sensor response is linear with solute mass over at least 2-3 decades and provides detection limits of 20-50 ng for the vapors tested. The combination of atmospheric-pressure air as carrier gas, modest operating pressures, and SAW sensor detection is well-suited for field instrumentation since it eliminates the need for support gases, permits smaller, low-power pumps to be used, and provides sensitivity to a wide range of vapor analytes.

A dual-adsorbent preconcentrator for a portable indoor-VOC microsensor system.

The development and testing of a miniature dual-adsorbent preconcentrator for a microsensor-based analytical system designed to determine complex volatile organic chemical (VOC) mixtures encountered in indoor working environments at low part-per-billion levels is described. Candidate adsorbents were screened for thermal-desorption bandwidth and breakthrough volume against 20 volatile organic vapors and subsets thereof as a function of several relevant variables. A glass capillary (1.1 mm i.d.) packed with 3.4 mg of Carbopack X and 1.2 mg of Carboxen 1000 provides sufficient capacity for a 1-L dry-air sample containing all 20 vapors at concentrations of 100 ppb as well as providing a composite half-height peak width of <3 s at a desorption temperature of 300 degrees C and a flow rate of 4 mL/min. Required adsorbent masses increase to 7.0 and 1.5 mg, respectively, for the same mixture at component concentrations of 1 ppm. Vapor breakthrough volumes for the Carbopack X are unaffected by humidity from 0 to 100%RH, but those for the Carboxen 1000 are significantly reduced, requiring an additional 0.9 mg of the latter to avoid premature breakthrough at the 100 ppb level. Good peak shapes, efficient chromatographic separation of preconcentrated sample mixture components, and detection limits in the low-parts-per-billion range using an integrated surface-acoustic-wave (SAW) sensor are achieved. Preconcentrator design and operating parameters are considered in terms of the vapor bed-residence times and breakthrough volumes in the context of the modified Wheeler equation.

Use of linear solvation energy relationships for modeling responses from polymer-coated acoustic-wave vapor sensors.

The applicability and performance of linear solvation energy relationships (LSERs) as models of responses from polymer-coated acoustic-wave vapor sensors are critically examined. Criteria for the use of these thermodynamic models with thickness-shear-mode resonator (TSMR) and surface-acoustic-wave (SAW) vapor sensors are clarified. Published partition coefficient values derived from gas-liquid chromatography (GLC) are found to be consistently lower than those obtained gravimetrically, in accordance with previous reports, suggesting that LSERs based on GLC-derived partition coefficients will not provide accurate estimates of acoustic-wave sensor responses. The development of LSER models directly from polymer-coated TSMR vapor sensor response data is demonstrated and a revised model developed from SAW vapor sensor response data, which takes account of viscoelastic changes in polymeric coating films, is presented and compared to those developed by other methods.

High-speed analysis of complex indoor VOC mixtures by vacuum-outlet GC with air carrier gas and programmable retention.

A pressure-tunable, series-coupled column ensemble was used with atmospheric pressure air as carrier gas for the vacuum-outlet GC analysis of 42 volatile and semivolatile organic compounds commonly encountered as indoor air pollutants. Separation strategies applicable to a field-portable instrument that will employ a dual-stage preconcentrator and a microsensor array as the detector were developed, where coelution of certain analytes can be tolerated. The capillary column ensemble consists of a 4.5-m segment of nonpolar dimethyl polysiloxane followed by a 7.5-m segment of polar trifluoropropylmethyl polysiloxane. Good long-term thermal stability of the column ensemble was observed for continuous operation in air at temperatures up to 210 degrees C. A computer-driven pressure controller at the column junction point is used to adjust vapor retention for specified sets of target compounds. The compounds were divided into two groups according to retention order, and high-speed analysis conditions were determined for the two groups individually as well as for the entire mixture. The earlier eluting group of 21 compounds was analyzed isothermally at 30 degrees C in about 160 s using a single, on-the-fly junction-point pressure change during the separation. The later eluting group of 21 compounds was analyzed in about 200 s with temperature programming and a constant (tuned) junction-point pressure. The entire mixture was analyzed in about 400 s using a two-step temperature program and a three-step pressure program, with minimal overlap in eluting peaks. Separations are adequate for analysis by a sensor array capable of discriminating among small groups of coeluting vapors on the basis of their response patterns.

Temperature and humidity compensation in the determination of solvent vapors with a microsensor system.

Accounting for changes in temperature and ambient humidity is critical to the development of practical field vapor-monitoring instrumentation employing microfabricated sensor arrays. In this study, responses to six organic vapors were collected from two prototype field instruments over a range of ambient temperatures and relative humidities (RH). Each instrument contains an array of three unthermostated polymer-coated surface acoustic wave (SAW) resonators, a thermally desorbed adsorbent preconcentrator bed, a reversible pump and a small scrubber cartridge. Negligible changes in the vapor sensitivities with atmospheric RH were observed owing, in large part, to the temporal separation of co-adsorbed water from the organic vapor analytes upon thermal desorption of preconcentrated air samples. As a result, calibrations performed at one RH level could be used to determine vapors at any other RH without corrections using standard pattern recognition methods. Negative exponential temperature dependences that agreed reasonably well with those predicted from theory were observed for many of the vapor-sensor combinations. It was possible to select a subset of sensors with structurally diverse polymer coatings whose sensitivities to all six test vapors and selected binary vapor mixtures had similar temperature dependences. Thus, vapor recognition could be rendered independent of temperature and vapor quantification could be corrected for temperature with sufficient accuracy for most applications. The results indicate that active temperature control is not necessary and that temperature and RH compensation is achievable with a relatively simple microsensor system.

The fractional free volume of the sorbed vapor in modeling the viscoelastic contribution to polymer-coated surface acoustic wave vapor sensor responses.

Surface acoustic wave (SAW) vapor sensors with polymeric sorbent layers can respond to vapors on the basis of mass loading and modulus decreases of the polymer film. The modulus changes are associated with volume changes that occur as vapor is sorbed by the film. A factor based on the fractional free volume of the vapor as a liquid has been incorporated into a model for the contribution of swelling-induced modulus changes to observed SAW vapor sensor responses. In this model, it is not the entire volume added to the film by the vapor that contributes to the modulus effect; it is the fractional free volume associated with the vapor molecules that causes the modulus to decrease in a manner that is equivalent to free volume changes from thermal expansion. The amplification of the SAW vapor sensor response due to modulus effects that are predicted by this model has been compared to amplification factors determined by comparing the responses of polymer-coated SAW vapor sensors with the responses of similarly coated thickness shear mode (TSM) vapor sensors, the latter being gravimetric. Results for six to eight vapors on each of two polymers, poly(isobutylene) and poly(epichlorohydrin), were examined. The model predicts amplification factors of the order of about 1.5-3, and vapor-dependent variations in the amplification factors are related to the specific volume of the vapor as a liquid. The fractional free volume factor provides a physically meaningful addition to the model and is consistent with conventional polymer physics treatments of the effects of temperature and plasticization on polymer modulus.

Personal monitoring instrument for the selective measurement of multiple organic vapors.

Development and laboratory testing of a small instrument capable of recognizing and quantifying multiple organic vapors at low- and sub-ppm concentrations is described. The instrument is slightly larger than a standard personal sampling pump and employs an array of three polymer-coated surface-acoustic-wave microsensors for vapor detection. Vapors are first trapped on a miniature adsorbent preconcentrator housed within the instrument and then thermally desorbed for analysis by the microsensor array. Each measurement cycle requires 5.5 min. The collective responses from the array are stored and then analyzed using pattern recognition methods to yield the identities and concentrations of collected vapors and vapor mixture components. Following initial optimization of instrument operating parameters, calibrations were performed with 16 organic solvent vapors and selected mixtures to establish a response library for each of two identical instruments. Limits of detection < or = 0.1 x threshold limit value were obtained for most vapors. In a series of 90 subsequent exposure tests, vapors were recognized with an error of < 6% (individual vapor challenges) and < 16% (binary mixture challenges) and quantified with an average error of < 10%. Monte Carlo simulations were coupled with pattern recognition analyses to predict the performance for many possible vapor mixtures and sensor combinations. Predicted recognition errors ranged from < 1 to 24%. Performance is shown to depend significantly on the interfacial polymer layers deposited on the sensors in the array and the nature and complexity of the vapor mixtures being analyzed. Results establish the capability of this technology to provide selective multivapor monitoring of personal exposures in workplace environments.

Determination of solvents permeating through chemical protective clothing with a microsensor array.

The performance of a novel prototype instrument in determining solvents and solvent mixtures permeating through samples of chemical protective clothing (CPC) materials was evaluated. The instrument contains a mini-preconcentrator and an array of three polymer-coated surface-acoustic-wave (SAW) microsensors whose collective response patterns are used to discriminate among multiple permeants. Permeation tests were performed with a 2.54 cm diameter test cell in an open-loop configuration on samples of common glove materials challenged with four individual solvents, three binary mixtures, and two ternary mixtures. Breakthrough times, defined as the times required for the permeation rate to reach a value of 1 microg cm(-2) min(-1), determined by the instrument were within 3 min of those determined in parallel by manual sampling and gas chromatographic analysis. Permeating solvents were recognized (identified) from their response patterns in 59 out of 64 measurements (92%) and their vapor concentrations were quantified to an accuracy of +/- 31% (typically +/- 10%). These results demonstrate the potential for such instrumentation to provide semi-automated field or bench-top screening of CPC permeation resistance.

Vapor recognition with small arrays of polymer-coated microsensors. A comprehensive analysis.

A comprehensive analysis of vapor recognition as a function of the number of sensors in a vapor-sensor array is presented. Responses to 16 organic vapors collected from six polymer-coated surface acoustic wave (SAW) sensors were used in Monte Carlo simulations coupled with pattern recognition analyses to derive statistical estimates of vapor recognition rates as a function of the number of sensors in the array (< or = 6), the polymer sensor coatings employed, and the number and concentration of vapors being analyzed. Results indicate that as few as two sensors can recognize individual vapors from a set of 16 possibilities with < 6% average recognition error, as long as the vapor concentrations are > 5 x LOD for the array. At lower concentrations, a minimum of three sensors is required, but arrays of 3-6 sensors provide comparable results. Analyses also revealed that individual-vapor recognition hinges more on the similarity of the vapor response patterns than on the total number of possible vapors considered. Vapor mixtures were also analyzed for specific 2-, 3-, 4-, 5-, and 6-vapor subsets where all possible combinations of vapors within each subset were considered simultaneously. Excellent recognition rates were obtainable for mixtures of up to four vapors using the same number of sensors as vapors in the subset. Lower recognition rates were generally observed for mixtures that included structurally homologous vapors. Acceptable recognition rates could not be obtained for the 5- and 6-vapor subsets examined, due, apparently, to the large number of vapor combinations considered (i.e., 31 and 63, respectively). Importantly, increasing the number of sensors in the array did not improve performance significantly for any of the mixture analyses, suggesting that for SAW sensors and other sensors whose responses rely on equilibrium vapor-polymer partitioning, large arrays are not necessary for accurate vapor recognition and quantification.

Establishing a limit of recognition for a vapor sensor array.

Organic vapor analysis with microsensor arrays relies principally on two output parameters: the response pattern, which provides qualitative information, and the response sensitivity, which determines the limit of detection (LOD). The latter is used to define the operating limit in the low-concentration range, under the implicit assumption that, if a vapor can be detected, it can be identified and differentiated from other vapors on the basis of its response pattern. In this study, the performance of an array of four polymer-coated surface acoustic wave vapor sensors was explored using calibrated response data from 16 solvent vapors in Monte Carlo simulations coupled with pattern recognition analysis. The statistical modeling revealed that the ability to recognize a vapor from its response pattern decreases with decreasing vapor concentration, as expected, but also that the concentration at which errors in vapor recognition become excessive is well above the calculated LOD in most cases, despite the LOD being based on the least sensitive sensor in the array. These results suggest the adoption of a limit of recognition (LOR), defined as the concentration below which a vapor can no longer be reliably recognized from its response pattern, as an additional criterion for evaluating the performance of multisensor arrays. A generalized method for estimating the LOR is presented, as well as a means for improving the LOR via residual error analysis.

ASTM F739 method for testing the permeation resistance of protective clothing materials: critical analysis with proposed changes in procedure and test-cell design.

ASTM (American Society for Testing and Materials) Method F739-96 specifies a test-cell design and procedures for measuring the permeation resistance of chemical protective clothing. Among the specifications are open-loop collection stream flow rates of 0.050 to 0.150 L/min for a gaseous medium. At elevated temperatures the test must be maintained within 1 degree C of the set point. This article presents a critical analysis of the effect of the collection stream flow rate on the measured permeation rate and on the temperature uniformity within the test cell. Permeation tests were conducted on four polymeric glove materials with 44 solvents at 25 degrees C. Flow rates > 0.5 L/min were necessary to obtain accurate steady-state permeation rate (SSPR) values in 25 percent of the tests. At the lower flow rates the true SSPR typically was underestimated by a factor of two or less, but errors of up to 33-fold were observed. No clear relationship could be established between the need for a higher collection stream flow rate and either the vapor pressure or the permeation rate of the solvent, but test results suggest that poor mixing within the collection chamber was a contributing factor. Temperature gradients between the challenge and collection chambers and between the bottom and the top of the collection chamber increased with the water-bath temperature and the collection stream flow rate. Use of a test cell modified to permit deeper submersion reduced the gradients to < or = 0.5 degrees C. It is recommended that all SSPR measurements include verification of the adequacy of the collection stream flow rate. For testing at nonambient temperatures, the modified test cell described here could be used to ensure temperature uniformity throughout the cell.

Prototype instrument employing a microsensor array for the analysis of organic vapors in exhaled breath.

A prototype portable instrument capable of selectively measuring organic vapors in breath at low- and sub-ppm concentrations was tested. The instrument employs an array of four polymer-coated surface-acoustic-wave (SAW) resonators and microprocessor-controlled pumps, valves, and heating elements for preconcentration and thermal desorption of breath samples. Response data are passed to an external personal computer for processing. Sensor responses are based on the reversible changes in the mass and viscoelasticity of the polymeric coatings accompanying vapor sorption. Calibrations were performed for perchloroethylene, trichloroethylene, and methoxyflurane at 100% relative humidity using 15 mg of TenaxTA as the preconcentrator adsorbent. Analyses were then conducted of 250-mL breath samples prepared in Tedlar bags spiked with one of the three solvents within the range of 2 to 18 ppm. Differences between concentrations measured using the prototype instrument and those measured by gas chromatography ranged from -6 to 17% for perchloroethylene. Similar results were obtained for trichloroethylene and methoxyflurane with larger differences occurring at lower concentrations. Estimated limits of detection of 0.7, 0.6, and 4 ppm were achieved for perchloroethylene, trichloroethylene, and methoxyflurane, respectively. These preliminary results demonstrate the feasibility of using SAW sensor technology for field breath analysis.

Effects of temperature and humidity on the performance of polymer-coated surface acoustic wave vapor sensor arrays.

The influences of temperature and atmospheric humidity on the performance of an array of eight polymer-coated 158-MHz surface acoustic wave vapor sensors were investigated. Sensitivities to the seven organic vapors examined all exhibited negative Arrhenius temperature dependencies, with responses increasing by factors of 1.5-4.4 on going from 38 to 18 degrees C. The magnitudes of the temperature effects, while generally similar, differed sufficiently among certain sensor-vapor combinations to cause marked changes in vapor response patterns. In addition, it was found that operating identically coated sensors at different temperatures could provide a means for discriminating certain vapors. The changes in sensor responses with temperature agreed reasonably well with those expected assuming ideal vapor sorption behavior and indicated that changes in the moduli of the sensor coatings were not important mediating factors. Responses to relative humidity (RH) from 0 to 85% RH were important even for the nonpolar sensor coatings. Significant changes in the sensitivities to the organic vapors were observed as a function of atmospheric humidity for several sensor-vapor combinations, which, in turn, affected the patterns of responses obtained from the sensor array. Results indicate that small changes in temperature or humidity have a larger effect on baseline stabilities than on the responses to the vapors. Monte Carlo simulations of sensor responses show that the ability to discriminate vapors in binary and ternary mixtures using a four-sensor array remains high regardless of the operating temperature and ambient humidity, provided that temperature-or humidity-induced changes in the response patterns are taken into account.

Respiratory health in asbestos-exposed ironworkers.

This study aimed to determine the prevalence of respiratory morbidity among asbestos-exposed ironworkers and to determine the relationship between respiratory morbidity indices and length of exposure. A medical screening provided information on chest radiographic abnormalities, pulmonary function, rales, finger clubbing, and respiratory symptoms for 547 asbestos-exposed ironworkers. Union pension records furnished data on length of exposure. The study group exhibited on increased prevalence of small irregular opacities, pleural plaques, and pleural thickening on chest x-ray; reduced FEF 25-75; rales; and respiratory symptoms. After controlling for the effect of cigarette smoking and age, years since joining the ironworkers union were significantly associated with profusion, pleural thickening, pleural plaques, rales, percent predicted FVC, reduced FVC, reduced FEV1, reduced FEV1/FVC, and dyspnea grades I, II, III, and IV.