2007 Progress 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 Period Covered by this Report: January 1, 2007 through December 31,2007
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.

Progress Summary:

This grant was originally made available during the tenure of the PI at Texas Tech University. In August of 2006, the grant was formally closed out at Texas Tech and the novation process begun. Funds were in place at the University of Texas at Arlington by January 2007.

Summary of published material

Since the last report was submitted highlights of published work wholly or partly sponsored by this project are as follows:

Two generations of gas particle ion chromatography systems (GPIC) systems were developed in this work. In the first analyzer, we used a short separation column, an isocratic carbonate eluent and post suppressor CO2 removal (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 are used. In one channel, a wet denuder collects 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 collects and extracts the soluble components of PM2.5. The aqueous particle extract is aspirated by a peristaltic pump onto serial cation and anion preconcentrator columns. Gas samples are similarly loaded onto another set of serial ation and anion preconcentrator columns. The cation preconcentrator is eluted with NaOH and the evolved NH3 is passed across a membrane device whence it diffuses substantially into a deionized water receptor stream; the conductivity of the latter provides a measure of NH3 (NH4+). The anion preconcentrator column(s) are subjected to automated periodic analysis by ion chromatography. This system provides data every 30 min for both particles (NO3-,SO42 and NH4+) and gases (HNO3, SO2 and NH3). Gas and particle extract samples are each collected for 15 min. The analyses of the gas and particle samples are staggered 15 min apart. The limit of detection (S/N = 3) for NO3, SO42 and NH4+ are 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 has separate sampling channels for gases and particles. In one, a membrane denuder collects soluble gases for preconcentration and analysis. In the other, a cyclone removes larger particles, a membrane denuder removes soluble gases and a continuously wetted hydrophilic filter collects particles. A single, multiport, syringe pump handles liquid transport, and one conductivity detector measures anions and ammonium for both channels. Electrodialytically generated gradient hydroxide eluent permits 20 min chromatographic runs. Gas/particle samples are each collected for 40 min, but the sampling intervals are staggered by 20 min. Liquid samples from the gas denuder and particle collector are 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 results in an ammonium peak before anion peaks in the chromatogram. The system measures 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/m3 limits of detection (LODs) are 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 was 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.

Isoprene is the dominant hydrocarbon from vegetative emissions is one of the main sources of oxalate/oxalic acid. It is also the prevalent hydrocarbon in breath – Isoprene is involved in the biosynthetic pathway to cholesterol. We investigated the merits and pitfalls of breath isoprene measurement via its chemiluminescence (CL) reaction of with ozone. In many cases apparent concentrations measured were higher than those obtained by a gas chromatography (GC) reference method that can be traced to ozone induced CL with simultaneously present lower olefins and sulfur compounds. A warm column preconcentration method eliminated the lower olefins and greatly improved sensitivity while a silver-form ion exchange resin could remove the sulfur gases. The breath sample was captured on a miniature synthetic carbon sorbent column maintained at 55°C, under which conditions ethylene, propylene and water vapor are not significantly captured while the preconcentration process greatly improved the limit of detection (LOD) for isoprene to 0.6 ppbv (S/N=3). The captured isoprene was released by heating the column to 150°C. Samples were analyzed in a double-blind fashion in our laboratory and at EPA-RTP, the latter laboratory performing quantitation by cryofocusing gas chromatography (GC) -flame ionization detection (FID) with parallel measurement by mass spectrometry (MS) to provide identity confirmation. The CL and the GC results agreed when both warm column preconcentration and passage through Ag+-form cation exchange resin, which removes divalent sulfur gases, were implemented prior to CL measurement. The intensity of CL from the reaction with ozone can be much higher for some sulfur gases than for isoprene. Even though present at lower concentrations than isoprene, unless removed prior to CL measurement, for some individuals sulfur gases can cause unacceptably large (up to 500%) errors, making the sulfur gas removal step critical.

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 suggest that oxalate does not solely originate in the gas phase and condense into particles. Gaseous H2Ox concentrations are much lower than particulate Ox concentrations and are well correlated with HNO3, HCHO, and O3 supporting a photochemical origin. Of special relevance to the Tampa Bay region is the extent of nitrogen deposition in the Tampa bay estuary. Hydroxyl radical is primarily responsible for the conversion of NO2 to HNO3, the latter being much more easily deposited. Hydroxyl radical is also responsible for the aqueous phase formation of oxalic acid from alkenes where isoprene is a primary source. We postulated that an estimate of ·OH can be obtained from H2Ox/Ox production rate and we accordingly show that the product of total oxalate concentration and NO2 concentration approximately predicts the total nitrate concentration during the same period.

The nitric acid that is produced as described above can react with NaCl particles in a coastal atmosphere as in Tampa. To form NaNO3 and 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 US Either soot carbon or ammonium nitrate can contribute equally to visibility reduction. Measurement of low levels of ammonia has been difficult. We developed a robust, highly sensitive instrument for the determination of ambient ammonia. The instrument uses two syringe pumps to handle three liquids. The flow configuration is 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 is 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 is 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-min cycles over 9 days showed excellent overall precision (n = 1544, pNH3 = 5 ppbv, RSD = 3%). Precision for liquid-phase injections is even better (n =1520, [NH4+(aq)] = 2.5μM, RSD = 2%). The response is relatively humidity independent; it decreases by 3.6% from 20 to 80% relative humidity.


Journal Articles on this Report : 7 Displayed | Download in RIS Format

Other project views: All 46 publications 22 publications in selected types All 22 journal articles
Type Citation Project Document Sources
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)
  • Abstract from PubMed
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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)
    R831074 (2007)
    R831074 (2008)
    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)
    R827993 (Final)
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  • Abstract: Taylor and Francis-Abstract
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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)
    R831074 (Final)
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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 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)
    R831074 (2007)
    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,, 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, air quality modeling, health effects, particle size, carbon aerosols, atmospheric particulate matter, human health effects, PM 2.5, atmospheric particles, aerosol particles, mass spectrometry, ambient air monitoring, air quality models, exposure, air modeling, emissions, thermal desorption, molecular markers, gas chromatography, air sampling, carbon particles, air quality model, human exposure, ambient particle health effects, particulate matter mass, aethalometric liquid chromatographic mass spectrometry, aersol particles, monitoring of organic particulate matter, aerosol analyzers, human health risk, measurement methods

    Relevant Websites:

    No specific website solely devoted to the project has been established but the PI’s website contain detailed lists of publications, etc: http://www3.uta.edu/faculty/dasgupta/index.htm exit EPA

    Progress and Final Reports:

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