Final Report: Aethalometric Liquid Chromatographic Mass Spectrometric Instrument

EPA Grant Number: R831074
Title: Aethalometric Liquid Chromatographic Mass Spectrometric Instrument
Investigators: Dasgupta, Purnendu K.
Institution: The University of Texas at Arlington
EPA Project Officer: Chung, Serena
Project Period: September 1, 2003 through December 31, 2007 (Extended to December 31, 2008)
Project Amount: $450,000
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text |  Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter

Objective:

To fabricate, evaluate, and field test new instrumentation that can provide more information on the speciation of carbonaceous compounds in the atmosphere.

Summary/Accomplishments (Outputs/Outcomes):

Specific Activities and Details
2004-2005
A membrane-based denuder coupled particle collector and ion analysis system was built and deployed in Bondville, IL This instrument provided information on all major ionogenic gas composition and corresponding particle anionic compositions plus ammonium. Unlike previous instruments of this type, this instrument determines not only inorganic gases and particles, but also provides measures of acetic, formic, and oxalic acids and the corresponding particle phase organic acid anions, including methanesulfonate. This instrument provides 40 minute time resolution, performs gradient ion chromatography, has a small footprint and uses a modest sampling rate of 1.5 liters per minute and still attains limits of detection (LODs) in the low ng/m3 range. Dionex Corporation has licensed marketing rights of the membrane denuder used in this instrument from the University (U.S. Patent No. 6,890,372).
 
A second copy of the above instrument was deployed in Beltsville, MD, for approximately 3 weeks and was compared with two commercial MARGA instruments being evaluated by the EPA. A membrane-based CO2 removal device was developed. This microvolume device removes CO2 near-quantitatively from an aqueous stream. This has been commercialized by Dionex Corporation and already has found considerable consumer acceptance. A size selective multiple wavelength aethalometer was developed. A 12 element LED-array ranging from 375-855 nm and a 512 element photodiode array was used. The geometry permitted both spectral measurement of the particles and the size distribution measurement of the particles. We have developed a means to classify water-soluble and insoluble carbon based on the ease with which it is oxidized to CO2 by liquid phase radical and photooxidation processes.
 
2006-2007
Two generations of gas particle ion chromatography (GPIC) systems were developed. In the first analyzer, we used a short separation column, an isocratic carbonate eluent and post suppressor CO2 removal device (a patented invention developed earlier in this project). Measured constituents included ammonium, nitrate, and sulfate in the particle fraction, and nitric acid, sulfur dioxide, and ammonia among soluble gases. Two independent sampling channels were used. In one channel, a wet denuder collected soluble gases. In the second channel, following removal of large particles by a cyclone and soluble gases by a wet denuder, a hydrophobic filter-based particle collector collected and extracted the soluble components of PM2.5. The aqueous particle extract was aspirated by a peristaltic pump onto serial cation and anion preconcentrator columns. Gas samples were similarly loaded onto another set of serial cation and anion
preconcentrator columns. The cation preconcentrator was eluted with NaOH and the evolved NH3 was passed across a membrane device when it diffused substantially into a deionized water receptor stream; the conductivity of the latter provided a measure of NH3 (NH4+ ). The anion preconcentrator column(s) were subjected to automated periodic analysis by ion chromatography. This system provided data every 30 min for both particles (NO3 -, SO42 and NH4+) and gases (HNO3, SO2, and NH3). Gas and particle extract samples were each collected for 15 minutes. The analyses of the gas and particle samples were staggered 15 minutes apart. The limit of detection (S/N = 3) for NO3, SO42, and NH4+ were 2.6, 5.3, and 2.1 ng/m3, respectively.
 
The second generation instrument was more sophisticated. It too measured ionic constituents in PM2.5 and water-soluble ionogenic gases. The instrument had separate sampling channels for gases and particles. In one, a membrane denuder collected soluble gases for preconcentration and analysis. In the other, a cyclone removed larger particles, a membrane denuder removed soluble gases and a continuously wetted hydrophilic filter collected particles. A single, multiport, syringe pump handled liquid transport, and one conductivity detector measured anions and ammonium for both channels. Electrodialytically generated gradient hydroxide eluent permitted 20-minute chromatographic runs. Gas/particle samples were each collected for 40 minutes, but the sampling intervals were staggered by 20 minutes. Liquid samples from the gas denuder and particle collector were aspirated and preconcentrated on sequential cation and anion concentrators and transferred respectively to an ammonia transfer device and an anion separation column. The flow configuration resulted in an ammonium peak before anion peaks in the chromatogram. The system measured ammonia, organic acids (such as acetic, formic, and oxalic acids), HCl, HONO, SO2, HNO3, and the corresponding ions in the aerosol phase. Low ng/m3 to sub-ng/mLODs were attained for most common gases and particulate constituents, the LODs for gaseous SO2 to NH3 range, for example, from sub parts per trillion by volume (sub-pptv) to ~5 pptv.
 
An early version of a GPIC system was deployed in Lindon, UT. One-hour averaged PM2.5 data were combined with continuous gas phase data to perform source apportionment according to the EPA UNMIX program. Sources of the particulate matter were apportioned into primary emission sources and secondary formation sources. Primary mobile sources including diesel and gasoline engine vehicles and one day-time and one night-time secondary source were identified.
 
Oxalic acid is the dominant dicarboxylic acid (DCA), and it constitutes up to 50% of total atmospheric DCAs, especially in non urban and marine atmospheres. It is an important member of atmospheric carbon compounds. We studied oxalate and oxalic acid distribution in Tampa, FL, using the gas-particle ion chromatograph sampling system developed in this project. A significant amount of particulate H2Ox/oxalate (Ox) occurred in the coarse particle fraction of a dichotomous sampler, the ratio of oxalate concentrations in the PM10 to PM2.5 fractions ranged from 1-2, with mean ± sd being 1.4±0.2. These results suggested that oxalate did not solely originate in the gas phase and condense into particles. Gaseous H2Ox concentrations were much lower than particulate Ox concentrations and were well correlated with HNO3, HCHO, and O3 supporting a photochemical origin. Of special relevance to the Tampa Bay region was the extent of nitrogen deposition in the Tampa Bay estuary. Hydroxyl radical was primarily responsible for the conversion of NO2 to HNO3, the latter being much more easily deposited. Hydroxyl radical also is responsible for the aqueous phase formation of oxalic acid from alkenes where isoprene is a primary source. We postulated that an estimate of •OH could be obtained from H2Ox/Ox production rate and we accordingly showed that the product of total oxalate concentration and NO2 concentration approximately predicts the total nitrate concentration during the same period.
 
The nitric acid that was produced as described above could react with NaCl particles in a coastal atmosphere as in Tampa to form NaNO3 with the liberation of HCl. One month of semi-continuous and simultaneous measurements of particulate chloride and nitrate and gaseous HCl and HNO3 concentrations were made with the instrument developed in this project. To help explain and interpret the observed time-dependent concentration and gas-to-particle phase partitioning behavior for the NaCl-HNO3 reaction, we applied the Aerosol Inorganics Model III (AIM) to the measurement data. Good agreement between model predictions and observations was found. Measurement and modeling results suggested that coarse-mode sea salt particles from the Atlantic Ocean arrived in the morning at the monitoring site when relative humidity (RH) was high and the nature of the equilibrium least favored the outgassing of HCl from the particles. As the RH dropped in the afternoon, the equilibrium favored outgassing of HCl and the particulate nitrate concentration increased even as the concentration of coarse particles decreased. This effect was tied to the change in the ratio of nitrate to chloride activity coefficients (γNO3-/γCl-) with RH. AIM simulations indicated that this ratio approached unity at high RH but could take on small values (~0.05) at the lowest RH observed here. Thus, the particle phase slightly favored nitrate over chloride at high RH and greatly favored it at lower RH. Modeling revealed how diurnal changes in RH can rapidly shift HNO3 concentrations from gas- to particle-phase and thus affect the distance over which nitrogen is transported.
 
Nitric acid also reacts with ammonia to form ammonium nitrate – one of the major sources of particulate matter and reduced visibility in parts of the United States. Either soot carbon or ammonium nitrate can contribute equally to visibility reduction. Measurement of low levels of ammonia was difficult. We developed a robust, highly sensitive instrument for the determination of ambient ammonia. The instrument used two syringe pumps to handle three liquids. The flow configuration was a hybrid between traditional flow injection (FI) and sequential injection (SI) schemes. This hybrid flow analyzer spends ~87% of its time in the continuous flow FI mode, providing the traditional FI advantages of high baseline stability and sensitivity. The SI fluid handling operation in the remaining time makes for flexibility and robustness. Atmospheric ammonia was collected in deionized water by a porous membrane diffusion scrubber at 0.2 L/min with quantitative collection efficiency, derivatized on-line to 1-sulfonatoisoindole, and measured by fluorometry. In the typical range for ambient ammonia (0-20 ppbv), response was linear (r2=0.9990) with a S/N=3 limit of detection of 135 pptv (15 nM for 500 μL of injected NH4+(aq)) with an inexpensive light emitting diode photodiode-based detector. Automated operation in continuously repeated, 8-minute cycles over 9 days showed excellent overall precision (n = 1544, pNH3 = 5 ppbv, RSD = 3%). Precision for liquid-phase injections was even better (n =1520, [NH4+(aq)] = 2.5 μM, RSD = 2%). The response was relatively humidity independent; it decreased by 3.6% from 20 to 80% relative humidity.
 
2008
A paper on a technique that addresses the mathematical resolution of incompletely resolved peaks that is directly relevant to chromatographic characterization of atmospheric particles was published. Two other papers that are related to the present project in an auxiliary fashion were published: these relate to a special class of carbonaceous particles, namely bacterial spores. A further relevant paper that relates to
the affordable simultaneous measurement of NO2, O3, and relative humidity was submitted.
 
Resolution of overlapped chromatographic peaks is generally accomplished by modeling the peaks as Gaussian or modified Gaussian functions. It is possible, even preferable, to use actual single analyte input responses for this purpose and a nonlinear least squares minimization routine such as that provided by Microsoft ExcelTM Solver then can provide the resolution. In practice, the quality of the results obtained varies greatly due to small shifts in retention time. It is shown that such deconvolution can be considerably improved if one or more of the response arrays are iteratively shifted in time.
 
Bacterial spore determination by Terbium(III)-dipicolinate luminescence has been reported by several investigators. We collected spore samples with a cyclone and extracted dipicolinic acid (DPA) in-line with hot aqueous dodecylamine, added Tb(III) in a continuous-flow system and detected the Tb(III)- DPA with a gated liquid core waveguide fluorescence detector with a flashlamp excitation source. The absolute LOD for the system was equivalent to 540 B. subtilis spores (for a 1.8 m3 sample volume [t = 2 h, Q = 15 L/min], concentration LOD is 0.3 spores/L air). Extant literature suggests that, from office to home settings, viable spore concentrations range from 0.1 to 10 spores/L; however, these data have never been validated. Previously reported semi-automated instrumentation had an LOD of 50 spores/L. The present system was tested at five different location settings in Lubbock, Texas. The apparent bacterial spore concentrations ranged from 9 to 700 spores/L and only occasionally exhibited the same trend as the simultaneously monitored total optical particle counts in the g0.5 μm size fraction. However, because the apparent spore counts sometimes were very large relative to the 0.5+ μm size particle counts, we investigated potential positive interferences. We show that aromatic acids are very likely large interferants. This interference typically constitutes ~70% of the signal and can be as high as 95%. It can be completely removed by prewashing the particles.
 
We also described an affordable gated fluorescence detection system to measure fluorescent compounds with long-lifetimes that uses a tuning fork chopper to block the intense excitation pulse from a flash lamp or short-lived fluorescence. A conventional non-gated inexpensive photosensor module was used to collect the luminescence signal. Using the long-lived luminescence from the terbium(III)–dipicolinic acid (DPA) chelate, we demonstrated an LOD of 120 pM for DPA. This system was not only an order of magnitude less expensive than an electronically gateable phototomultiplier tube (GPMT), it exhibited no evidence of gradual loss of sensitivity, due likely to photocathode fatigue and deterioration, observed with a GPMT.
 
We described a novel optical sensor for the simultaneous measurement of atmospheric nitrogen dioxide (NO2), ozone (O3), and relative humidity (RH). A silica gel thin layer chromatographic (TLC) plate with transparent backing and impregnated with 8-amino-1-naphthol-5-sulfonic acid (ANS) was used as the collection/sensor element. The plate transmittance was probed by three discrete light emitting diodes (LEDs) centered respectively at 442, 525, and 850 nm. The transmission of the plate changed reversibly at all three wavelengths as the RH around the plate changed; this was the basis for an RH sensor. The ANS on the plate reacted to form a brown and a pink colored product when it reacted with NO2 and O3, respectively. The sample air impinged on the plate via an entrance nozzle. The LEDs were turned on alternately and the light was brought to the impregnated face of the plate by a three-legged fiber optic. The transmitted light was detected on the obverse side of the plate. The 850 nm signal provided the RH value and optionally served as the reference measurement for the other two wavelengths; the NO2 and O3 reaction products did not absorb at 850 nm. The absorbance values at 442 and 525 nm were used to obtain NO2 and O3 concentrations from a pair of simultaneous equations. For a sampling period of 5 minutes, the LODs based on 3 times the standard deviation of blank responses were 0.64 and 0.42 ppbv for NO2 and O3, respectively. Data obtained with collocated commercial instruments (O3-induced chemiluminescence analyzer for NO2 and UV-absorption for O3) showed good agreement.

Conclusions:

Continuing Activities
This project ended on December 31, 2008. However, on our own we will complete two different projects that we have embarked on and which have been centerpieces of this project.
 
A fully automated measurement system for total carbon in aerosol samples has been developed. The instrument operates over prolonged periods with minimal attention. Particles down to 0.1 μm are collected in the bottom reservoir of a cyclone and transferred periodically to an annular quartz reactor. The transfer is accomplished by a syringe pump using a 5 mL holding loop that prevents the sample itself from getting into the syringe. The sample in the reactor undergoes sequential treatment that liberates CO2. Minimally, three stages of treatment are used while oxygen is bubbled through the reactor at a low flow rate (10 standard cm3 per minute). The first treatment step involves the addition of dilute H2SO4; this results in the liberation of dissolved CO2 and the decomposition of other inorganic carbonates into CO2. Next, the UV lamp (that contains both 254 and 185 nm lines) is turned on (this also leads to the formation of ozone) and easily photochemically oxidizable compounds (carbohydrates, e.g., levoglucosan, are typical examples) are next decomposed and lead to CO2 formation. As the final step, acidic persulfate is added that leads to the oxidation of all organic compounds we have tested (it also is a standard method of the measurement of organic carbon in water samples). Even in this final step, which appears to follow a first order oxidation process, different compounds discernibly oxidize at different rates from which further information can be gleaned about their nature. It is to be noted that elemental carbon, either in the form of graphite, activated carbon or buckminsterfullerene (C60) are resistant to oxidation by any of the above steps and are not measured by this system.
 
The CO2 produced is sensed by two sequential short-long diffusion scrubber (DS)-conductivity detectors operated in the stop-flow mode. Each contains a length of a hydrophobic porous membrane tube in a jacketed enclosure with stainless steel tubular termini that function as the detector electrodes. The short sensor, filled with a low concentration of LiOH solution, is the first in the gas flow stream and captures a relatively small amount of the CO2 in the gas stream while the long sensor contains a higher concentration of LiOH. In both sensors, as the CO2 is absorbed by the LiOH, Li2CO3 is formed and the conductivity decreases. The short sensor provides a S/N=3 LOD of 83 ng C, while the long sensor provides a large linear dynamic range.
 
The second project involves spectrally resolved size distribution of atmospheric aerosol particles. A size selective multiple wavelength aethalometer was developed - this has a 12 element LED array ranging from 375-850 nm and a 512 element photodiode array. We studied the spatial distribution pattern of colored particles of different sizes generated from dye and NaCl solutions by a vibrating orifice aerosol generator (VOAG). Four different dyes with different particle sizes were generated and were allowed to deposit sequentially on a single quartz filter paper and the results then were compared with those taken individually on different filter paper.
 
We generated monodisperse aerosols of four different dyes viz., Eriochrome Red B, Methylene Blue, Malachite Green, and Metanil Yellow of known spectral absorption and in different sizes with a vibrating orifice aerosol generator. Particle color distribution of these dyes obtained from aethalometer were compared with the absorbance spectra of respective dye solutions obtained from spectrophotometer.
 
Large size particles show a rapid decrease in absorbance with change in pixel number from the nozzle position. Efforts will be made to ascertain whether a Gaussian, exponentially modified Gaussian or an exponential fit best fits the absorbance vs. pixel number and how this can be processed to yield the size mode of the particles. Figure 5 shows the absorbance spectra of 0.01 mM Eriochrome Red B dye particles of different sizes (0.37 μm, 0.40 μm, 0.80 μm, and 1.21 μm.
 
We also checked on additivity using MS Excel Solver; the same color A aerosol in size 1 and color B aerosol in size 2 were deposited singly on two different filters and sequentially on the same filter to check that within the reproducibility offered by the VOAG, 1 +2 = (1+2). 


Journal Articles on this Report : 21 Displayed | Download in RIS Format

Other project views: All 46 publications 22 publications in selected types All 22 journal articles
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Journal Article Amornthammarong N, Jakmunee J, Li J, Dasgupta PK. Hybrid fluorometric flow analyzer for ammonia. Analytical Chemistry 2006;78(6):1890-1896. R831074 (2007)
R831074 (Final)
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  • Journal Article Arnold JR, Hartsell BE, Luke WT, Ullah SMR, Dasgupta PK, Huey LG, Tate P. Field test of four methods for gas-phase ambient nitric acid. Atmospheric Environment 2007;41(20):4210-4226. R831074 (2006)
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  • Journal Article Berg JM, James DL, Berg CF, Toda K, Dasgupta PK. Gas collection efficiency of annular denuders:a spreadsheet-based calculator. Analytica Chimica Acta 2010;664(1):56-61. R831074 (Final)
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  • Journal Article Dasgupta PK, Li J, Zhang G, Luke WT, McClenny WA, Stutz J, Fried A. Summertime ambient formaldehyde in five U.S. metropolitan areas:Nashville, Atlanta, Houston, Philadelphia, and Tampa. Environmental Science & Technology 2005;39(13):4767-4783. R831074 (2005)
    R831074 (Final)
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  • Journal Article Dasgupta PK, Campbell SW, Al-Horr RS, Ullah SMR, Li J, Amalfitano C, Poor ND. Conversion of sea salt aerosol to NaNO3 and the production of HCl:analysis of temporal behavior of aerosol chloride/nitrate and gaseous HCl/HNO3 concentrations with AIM. Atmospheric Environment 2007;41(20):4242-4257. R831074 (2006)
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  • Journal Article Dasgupta PK. Chromatographic peak resolution using Microsoft Excel Solver. The merit of time shifting input arrays. Journal of Chromatography A 2008;1213(1):50-55. R831074 (2008)
    R831074 (Final)
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  • Journal Article Eom IY, Dasgupta PK. Frequency-selective absorbance detection:Refractive index and turbidity compensation with dual-wavelength measurement. Talanta 2006;69(4):906-913. R831074 (Final)
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  • Journal Article Grover BD, Carter CB, Kleinman MA, Richards JS, Eatough NL, Eatough DJ, Dasgupta PK, Al-Horr R, Ullah SMR. Monitoring and source apportionment of fine particulate matter at Lindon, Utah. Aerosol Science and Technology 2006;40(10):941-951. R831074 (2007)
    R831074 (Final)
    R827993 (2002)
    R827993 (2003)
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  • Journal Article Li J, Dasgupta PK, Luke W. Measurement of gaseous and aqueous trace formaldehyde:revisiting the pentanedione reaction and field applications. Analytica Chimica Acta 2005;531(1):51-68. R831074 (2005)
    R831074 (Final)
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  • Journal Article Li Q, Dasgupta PK, Temkin HK. Airborne bacterial spore counts by terbium-enhanced luminescence detection:pitfalls and real values. Environmental Science & Technology 2008;42(8):2799-2804. R831074 (2008)
    R831074 (Final)
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  • Journal Article Li Q, Dasgupta PK, Temkin H. A time-gated fluorescence detector using a tuning fork chopper. Analytica Chimica Acta 2008;616(1):63-68. R831074 (2008)
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  • Journal Article Lu C, Rashinkar SM, Dasgupta PK. Semicontinuous automated measurement of organic carbon in atmospheric aerosol samples. Analytical Chemistry 2010;82(4):1334-1341. R831074 (Final)
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  • Journal Article Luke WT, Arnold JR, Watson TB, Dasgupta PK, Li J, Kronmiller K, Hartsell BE, Tamanini T, Lopez C, King C. The NOAA Twin Otter and its role in BRACE: a comparison of aircraft and surface trace gas measurements. Atmospheric Environment 2007;41(20):4190-4209. R831074 (2006)
    R831074 (Final)
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  • Journal Article Luke WT, Arnold JR, Gunter RL, Watson TB, Wellman DL, Dasgupta PK, Li J, Riemer D, Tate P. The NOAA Twin Otter and its role in BRACE: platform description. Atmospheric Environment 2007;41(20):4177-4189. R831074 (2006)
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  • Journal Article Martinelango PK, Dasgupta PK, Al-Horr RS. Atmospheric production of oxalic acid/oxalate and nitric acid/nitrate in the Tampa Bay airshed:parallel pathways. Atmospheric Environment 2007;41(20):4258-4269. R831074 (2006)
    R831074 (2007)
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  • Journal Article Ohira S-I, Li J, Lonneman WA, Dasgupta PK, Toda K. Can breath isoprene be measured by ozone chemiluminescence? Analytical Chemistry 2007;79(7):2641-2649. R831074 (2007)
    R831074 (Final)
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  • Journal Article Ohira S, Dasgupta PK, Schug KA. Fiber optic sensor for simultaneous determination of atmospheric nitrogen dioxide, ozone, and relative humidity. Analytical Chemistry 2009;81(11):4183-4191. R831074 (Final)
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  • Journal Article Ullah SMR, Williams A, Dasgupta PK. Automated low-pressure carbonate eluent ion chromatography system with postsuppressor carbon dioxide removal for the analysis of atmospheric gases and particles. Aerosol Science and Technology 2005;39(11):1072-1084. R831074 (2005)
    R831074 (2006)
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  • Journal Article Takeuchi M, Rahmat Ullah SM, Dasgupta PK, Collins DR, Williams A. Continuous collection of soluble atmospheric particles with a wetted hydrophilic filter. Analytical Chemistry 2005;77(24):8031-8040. R831074 (2005)
    R831074 (2006)
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  • Journal Article Tian K, Dasgupta PK. A permeable membrane capacitance sensor for ionogenic gases:Application to the measurement of total organic carbon. Analytica Chimica Acta 2009;652(1-2):245-250. R831074 (Final)
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  • Journal Article Ullah SMR, Takeuchi M, Dasgupta PK. Versatile gas/particle ion chromatograph. Environmental Science & Technology 2006;40(3):962-968. R831074 (2006)
    R831074 (2007)
    R831074 (Final)
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  • Supplemental Keywords:

    aethalometry, ion chromatography, liquid chromatography, carbonaceous particles, atmospheric aerosols, oxidation to CO2, membrane transfer, conductometry, bacterial spores, gated fluorescence detection, chromatographic resolution, chromatographic overlap, multiwavelength size-discriminated aethalometry.
    , RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, air toxics, Environmental Chemistry, Air Pollution Effects, Risk Assessments, Monitoring/Modeling, Analytical Chemistry, Environmental Monitoring, Physical Processes, Engineering, Chemistry, & Physics, Environmental Engineering, carbon aerosols, air quality modeling, particle size, atmospheric particulate matter, health effects, aerosol particles, atmospheric particles, mass spectrometry, human health effects, ambient air monitoring, PM 2.5, air modeling, air quality models, exposure, air sampling, gas chromatography, thermal desorption, carbon particles, air quality model, emissions, molecular markers, particulate matter mass, human exposure, ambient particle health effects, aethalometric liquid chromatographic mass spectrometry, monitoring of organic particulate matter, aersol particles, particle dispersion, aerosol analyzers, measurement methods

    Relevant Websites:

    PI’s Website, which contains detailed information: http://www3.uta.edu/faculty/dasgupta/index.htmexit EPA

    Progress and Final Reports:

    Original Abstract
  • 2004 Progress Report
  • 2005 Progress Report
  • 2006 Progress Report
  • 2007 Progress Report
  • 2008 Progress Report