2006 Progress Report: Highly Time-Resolved Source Apportionment Techniques for Organic Aerosols Using the Aerodyne Aerosol Mass Spectrometer

EPA Grant Number: R832161
Title: Highly Time-Resolved Source Apportionment Techniques for Organic Aerosols Using the Aerodyne Aerosol Mass Spectrometer
Investigators: Jimenez, Jose-Luis , Hannigan, Michael P. , Schauer, James J. , Zhang, Qi
Institution: University of Colorado at Boulder , The State University of New York , University of Wisconsin - Madison
Current Institution: University of Colorado at Boulder , University of Wisconsin - Madison
EPA Project Officer: Chung, Serena
Project Period: December 1, 2004 through November 30, 2007 (Extended to November 30, 2008)
Project Period Covered by this Report: December 1, 2005 through November 30, 2006
Project Amount: $450,000
RFA: Source Apportionment of Particulate Matter (2004) RFA Text |  Recipients Lists
Research Category: Particulate Matter , Air Quality and Air Toxics , Air

Objective:

The overall objective of this 3-year research project is to develop, validate, and apply fine particulate matter (PM) source apportionment techniques for measurements made with the Aerodyne Aerosol Mass Spectrometer (AMS). The AMS is the only current real-time instrument that provides quantitative, size-resolved organic aerosol data with a time resolution of a few minutes or better. Prior results indicated that AMS organic aerosol data are sufficiently specific to address the critical need for source apportionment of organic aerosols with very high time resolution. We expect a number of instruments being developed to improve organic detection specificity via chemical ionization and/or photoionization. This project focuses on AMS data but will provide the foundation for using other such data for source apportionment.

Various approaches for apportioning AMS organic aerosol data will be investigated, including: (1) custom techniques that take advantage of our understanding of the data; (2) standard multivariate receptor models (e.g., UNMIX and positive matrix factorization [PMF]); and (3) Advanced Data Mining techniques currently being developed by the University of Wisconsin (under National Science Foundation [NSF] funding). All techniques will be tested with synthetic AMS data with several overlapping sources. We will then apply these methods to the well-characterized AMS datasets from the Pittsburgh, New York City, and Houston U.S. Environmental Protection Agency (EPA) Supersites. A new field campaign will be carried out (using three AMSs) with two objectives: (1) compare with the well-established chemical mass balance (CMB) method from collocated organic molecular marker data; and (2) demonstrate the improvements in organic source apportionment from three new techniques designed to improve the sensitivity and selectivity of the AMS for organic aerosols: a time-of-flight aerosol mass spectrometer (ToF-AMS) (replacing the quadrupole used in the standard AMS), vaporizer temperature cycling, and thermal denuding. The primary result of this project will be to demonstrate and validate source apportionment of organic aerosols with very high time resolution using AMS data. The results of this project can have a rapid and broad impact, because the techniques developed here can be applied to datasets acquired by many researchers around the world, including the more than 30 research groups with an AMS. In addition, these techniques and algorithms will also provide the foundation for source apportionment, using data from emerging and future quantitative aerosol mass spectrometers.

Progress Summary:

This project has two major components: (1) the development and application of receptor model techniques to AMS data; and (2) the field deployment and field data analysis for several new techniques aimed at obtaining more chemically specific information from the AMS for source apportionment purposes. Our work to date is successfully meeting the original goals of the project, as summarized below for each of the two major components.

Progress in Receptor Model Development and Application

During Year 1 of this project, a new data analysis technique (Custom Principal Component Analysis [CPCA]) was developed to deconvolve and quantify hydrocarbon-like and oxygenated organic aerosol (HOA and OOA) using highly time-resolved organic mass spectral data obtained with an Aerodyne AMS. This technique was applied successfully to the AMS data acquired at the EPA Pittsburgh Supersite in September 2002. The mass concentrations, temporal variations, size distributions, and mass spectra of HOA and OOA were obtained, and a detailed analysis of this information yields valuable insights into the sources and processes of atmospheric organic aerosols. This work is described in two publications (Zhang, et al., 2005a; Zhang, et al., 2005b). During Year 2, the CPCA was generalized to allow the extraction of more than two components, resulting in the Multiple Component Analysis (MCA) technique. The MCA has been applied to 37 highly time-resolved AMS datasets acquired in the Northern Hemisphere mid-latitudes in 11 urban areas, 5 regions downwind of urban areas, and 11 rural/remote locations (representative of high elevation, forested, pristine, and continentally influenced marine atmospheres). At most sites, the MCA retrieves several types of OOA. The results of this analysis, which are described in a submitted paper (Zhang, et al., submitted 2007), strongly indicate that global models largely underestimate the importance of Secondary organic aerosols (SOA) and overestimate the importance of primary organic aerosols (POA). The scientific community has shown very high interest in these results as evidenced by invitations to present them at two plenary lectures at the Gordon Research Conference on Atmospheric Chemistry and the Annual Conference of the American Association on Aerosol Research (AAAR). We have also used the CPCA results to evaluate the potential impact of acid-catalyzed SOA formation in the Pittsburgh dataset and concluded that an upper bound for this effect is a 25% increase in OOA mass (Zhang, et al., 2007).

The CPCA and MCA have also been applied to datasets from other AMS groups, resulting in several collaborative publications: Takegawa, et al. (2006) obtains good agreement between the HOA and OOA estimated with the AMS for Tokyo and a new technique for SOA estimation; Kondo, et al. (2007) concludes that about 90% of the OOA in Tokyo is water soluble, while HOA is water insoluble; and Cottrell, et al. (submitted, 2007) reports that OOA dominates the aerosol composition in rural New Hampshire, apparently due to SOA of both anthropogenic and biogenic origin.

In addition to the work on custom source apportionment techniques just described, we are vigorously pursuing the application of standard types of source apportionment techniques to AMS data. We are pursuing three techniques at this point:

(1) Graduate students from the Jimenez and Hannigan groups (Ingrid Ulbrich and Greg Brinkman) have developed a software shell (using Igor Pro 5) to automate running the Positive Matrix Factorization algorithm and show the detailed display and analysis of its results (PMF2). The software generates a wealth of diagnostic information to evaluate PMF solutions. We are evaluating PMF with synthetic AMS data, resulting in the identification of “mixing” and “splitting” errors that can also arise in the application of PMF to real data. In addition, PMF2 has been applied to the Pittsburgh dataset, largely confirming the previously published CPCA results, but also identifying a small (8%) semivolatile OOA II component. This work is described in a paper in preparation. The Igor-based PMF evaluation tool has been shared with AMS groups at Aerodyne, the University of Manchester (UK), and the University of California at Riverside (UCR), and is expected to become a standard in the AMS community (45 groups worldwide) once it is released next year.

(2) An Applied Math M.S. student, Josh Hemann, joined the source apportionment team over the past year. He has taken on uncertainty estimation as applied to PMF as his M.S. thesis. The latest version of the PMF software package (EPA PMF) has attempted to implement an uncertainty estimation approach— block bootstrapping of the input data to arrive at global source contribution uncertainty and source profile uncertainty. This implementation is not flexible, is prone to errors, and does not necessarily generate the desired results. Josh has used his applied math background to implement a newer version of the uncertainty estimation. He is using a naive Monte Carlo bootstrapping approach on the input matrix. The real improvement is that he is doing factor accounting, so that generates a distribution of source contributions (for each source) for each sample. The shape of these distributions will be used to tell the user how robust a specific application of PMF is to his/her input data.

(3) A collaboration has also been initiated with P. Paatero (University Helsinki) and P. Hopke (Clarkson University) to discuss our PMF2 results and to apply the Multilinear Engine (ME2) method to AMS data. So far, joint work has focused on the detailed evaluation of the uncertainty estimates required by PMF for the newer ToF-AMS instruments.

Progress in Acquiring and Analyzing More Chemically Specific Field Data

Two major accomplishments of Year 1 were the Study of Organic Aerosol in Riverside, phases 1 and 2 (SOAR-1 and SOAR-2) field experiments. These studies were organized by Professors Jimenez and Ziemann (UCR), with participation from Professors Schauer, Hannigan, and Zhang, to characterize organic aerosols with a variety of techniques. They were carried out at UCR, which is located in a polluted region downwind of Los Angeles that is heavily impacted by both primary and secondary aerosol. Although it was originally intended that this study would include only the UCR, University of Colorado, and University of Wisconsin groups, as word of our intentions spread, many other research groups became interested in making measurements with a variety of complementary methods during this period. As a result, during the SOAR-1 study (~ July 15–August 15, 2005), approximately 60 scientists from 17 universities and research institutes and companies participated in what is probably the most complete analysis of organic aerosols performed to date. During SOAR-2 (November 1–24, 2005), about 20 scientists from 8 groups participated. More detailed information on the participants and measurements can be found at http://cires.colorado.edu/jimenez-group/Field/Riverside05/ Exit . Four papers have been published so far based on the data acquired in this campaign by all participating groups, and at least eight more are submitted or in preparation.

During SOAR-1, the Jimenez group deployed four new instrument combinations for organic aerosol analysis: (1) a thermal denuder (TD) system was used in front of an AMS and a scanning mobility particle sizer (SMPS) to characterize the coupled chemistry-volatility profiles; (2) a new ToF-AMS was used to characterize the full size-composition space with high time resolution; (3) a new high-resolution (HR)-ToF-AMS was deployed in the field for the first time, to provide additional insight on the aerosol chemical composition by allowing the direct determination of the elemental composition of every peak in the spectrum of the AMS; and (4) a variable-temperature AMS vaporizer was used some of the time in both the ToF-AMS and HR-ToF-AMS to provide additional insight on the thermal properties of the organic aerosol. These systems were used to continuously analyze ambient particles and to analyze SOA formed in five reactions (pentadecane + OH/NOx, α-pinene + O3, 3-methyl-2-butenal + OH/NOx, toluene + OH/NOx, gasoline + OH/NOx) carried out in the environmental chamber in the Ziemann laboratory. During SOAR-2, the Jimenez group deployed the HR-ToF-AMS and the TD for ambient sampling for 3 weeks, and also carried out several additional chamber experiments. A paper has been published describing the HR-ToF-AMS instrument (DeCarlo, et al., 2006) and using SOAR-1 data to illustrate the capabilities of this instrument. Analysis of this extensive dataset is ongoing and has required the development of custom data analysis software, which will be described in an upcoming publication. AMS results indicate a very reproducible aerosol concentration and composition from day to day, with a similar diurnal cycle. Differences between weekday and weekends are observed, presumably due to changes in emissions. Under all conditions, SOA represents at least 2/3 of the organic aerosol in Riverside, based on both AMS and EC tracer analysis. A similar result holds for Pasadena during SOAR-1. This indicates that either SOA has been underestimated by most previous studies, or that the SOA/POA ratio has strongly increased with time over the last two decades. Analysis of the high-resolution spectra is ongoing, and we expect to quantitatively determine the elemental composition of the total OA and of the various components (HOA, OOA I, OOA II, etc.) based on the AMS spectra. Analysis of the TD and variable vaporizer temperature data from SOAR-1 is ongoing and will be presented in two forthcoming.

During SOAR-1, Professor Schauer’s group collected:

(1) 24-hour and 5–8-hour samples, which are being analyzed by gas chromatography-mass spectrometry (GC-MS) and other advanced techniques (high resolution GC-MS and liquid chromatography-mass spectrometry [LC-MS]). These data will be used to perform CMB-based source apportionment that will be compared to the AMS apportionment, and also to quantify acid concentrations and compare to the AMS OOAs (along the lines of Takegawa, et al., 2006).

(2) The Schauer group also deployed a real time elemental carbon/organic carbon (EC/OC) analyzer, which provided continuous data for most of the project, and whose data has been intercompared with the AMS organic matter (OM) with good results, and is being used in the analyses described above. Dr. Hannigan’s group deployed a Micro Orifice Uniform Deposit Impactor (MOUDI) during SOAR-1. While an AMS provides real-time analysis of aerosol size and composition, the MOUDI impactor requires post-sampling mass concentration and ion species analyses. During SOAR-1, a MOUDI and an AMS were run simultaneously. Gravimetric and ionic species analyses of the MOUDI collection surfaces, or substrates, are being performed using a precision balance and an ion chromatograph, respectively. Dr. Hannigan has generated mass concentration and ionic species size distributions for these MOUDI samples and has plans to integrate these results with AMS results over the coming summer. Comparing the mass concentration and particle size distribution results of these measurement tools should provide a greater understanding of their operating characteristics and biases of the different chemical characterization tools.

In addition, a $15,000 supplement to this grant funded Professor Weber of the Georgia Institute of Technology for deploying two organic aerosol analysis techniques during SOAR-1: (1) a real-time, water-soluble organic (WSOC) analyzer; and (2) filter collection followed by post-analysis of the acidic/neutral/basic fractions of the organic aerosol. Both instruments were successfully operated during the field study. The WSOC is being compared with the OC and AMS measurements to evaluate whether the results of Kondo, et al. (2007) for Tokyo aerosol are valid for Riverside. Preliminary results indicate lower solubility for the Riverside than the Tokyo OOA. Analysis of the filter samples is ongoing.

Other groups that participated in SOAR at no cost to this grant, and whose data for organic aerosols will be intercompared with the above methods, include the group of Professor Ziemann at UC R (Thermal Desorption Particle Beam Mass Spectrometer [TDPBMS]), the group of Professor Eatough at Brigham Young University (new EC/OC analyzer including a measurement of semi-volatile OC, filter dynamics measurement system [FDMS], tapered element oscillating microbalance [TEOM], and several other instruments), the group of Professor Goldstein at UC-Berkeley (Thermal Desorption Aerosol GC-MS, thermal desorption aerosol GC/MS-FID [TAG], and several gas-phase instruments), the group of Dr. Doug Worsnop at Aerodyne Research (two Soft Ionization ToF-AMSs), the group of Professor Sioutas at University of Southern California (USC) (versatile aerosol concentrator enrichment system [VACES] aerosol concentrator), the group of Suzanne Hering at Aerosol Dynamics (TAG and water condensation particle counters [CPCs]), the group of Professor Kim Prather at University of California (UC) at San Diego (three Aerodyne To F-AMSs and several other gas-phase and particle instruments), the group of Professors Janet Arey and Roger Atkinson at UC R (Filter + GC-MS analysis for polycyclic aromatic hydrocarbons [PAHs], Nitro-PAHs, and PAH reaction products), the group of Dr. Dennis Fitz at UCR (evaluation of PM bulk sampling artifacts, under a separate EPA Science To Achieve Results [STAR] grant), the group of Phil Hopke at Clarkson University (sampler for chemical analysis of oligomers), the group of Mark Thiemens at UC-San Diego (sulfate and nitrate isotope measurement), the group of Suzanne Paulson at University of California at Los Angeles (UCLA) (oxidants in particles), the group of Rafael Villalobos-Pietrini at the National Autonomous University of Mexico (UNAM; PAH analysis), and the group of Professor Seinfeld/Flagan (ambient sampling at California Institute of Technology with a ToF-AMS and several other instruments that provide a spatial point of comparison to Riverside). Preliminary data and insights were exchanged during a data analysis meeting held during the 2005 AAAR conference in Austin, TX, with participation from 10 of these groups. This rich combined dataset, including many state-of-the-art techniques for organic aerosol analysis, will provide insights on the relationship between the techniques and the nature and transformations of organic aerosols in urban areas. Its analysis is expected to provide improved data for understanding organic aerosol formation mechanisms and sources, and for use in source apportionment and airshed modeling. (Professors Griffin and Dabdub of University New Hampshire and UC-Irvine are interested in performing such modeling.) Such data and models can aid in the evaluation of the effects of fine PM on human health and the environment and can be used to develop more accurate air pollution models. This will allow for more efficient targeting of aerosol sources in pollution control strategies.

Finally, an additional field experiment (FLAME-1) was carried out in June 2006 at the U.S. Department of Agriculture Fire Sciences Laboratory in Missoula, MT. This experiment allowed us to obtain HR-ToF-AMS and TD signatures for smoke from 16 different biomasses at realistic dilution levels (1/10,000). Results indicate a wide variability in the organic fraction, composition, and volatility across biomasses and burning conditions (flaming vs. smoldering). Biomass burning organic aerosols (BBOA) are oxygenated, but less so than SOA. Most BBOA is also much more volatile than real-world SOA, and of similar volatility than urban POA.

Results from this campaign are being prepared for publication in at least two papers.

Nine journal papers that present work supported by and acknowledge this grant have been submitted: six have been published, one is “in press,” and two are undergoing peer review. Several additional papers are being written at present.

Future Activities:

Future Work in Receptor Model Development and Application

The plan for year 3 in the area of receptor model development and application includes:

(1)Submission of a paper analyzing the behavior of PMF2 for synthetic and real AMS data, and detailing the possible errors and uncertainties in this type of analysis.

(2) Further intercomparison of the MCA and PMF2 results for several ambient case studies. Two papers being readied for submission will address this topic, with the Houston EPA Supersite dataset and with data from Chebogue Pt., Nova Scotia, during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 campaign. Several other datasets from our group and from collaborators are also being analyzed.

(3) Application of the ME2 method to AMS data, and intercomparison with the results of MCA and PMF for well-characterized case studies, such as Pittsburgh, Houston, and Chebogue Pt. ME2 allows partial constraint in source profiles, which allows the exploration of “mixed PMF-CMB” models.

(4) Evaluation of the NUMFACT algorithm, which is also part of the UNMIX program and attempts to estimate the number of factors present in a dataset versus the results of the various receptor models.

(5) Further uncertainty analysis of PMF using the bootstrapping technique.

(6) Evaluation of whether the TD, high resolution, and variable temperature cycling data allow the identification of additional components for the organic aerosol.

Future Work in Acquiring and Analyzing More Chemically Specific Field Data

After the successful completion of the SOAR-1 and SOAR-2 field experiments, the focus of this area has shifted to the analysis of the enormous database collected, which is proceeding in collaboration with several of the groups involved. The analysis of the ToF-AMS and HR-ToF-AMS data has been slowed by the need to develop analysis algorithms and software, as this was one of the first deployments of the ToF-AMS and the first deployment of the HR-ToF-AMS by any group. The software and algorithms are now mostly developed, and will be the subject of an upcoming publication. Analysis is now progressing rapidly, and we expect to submit a first paper on the SOA versus POA fractions in Riverside and Pasadena by June 2007. Further analysis will compare the results from source apportionment using the ToF-AMS data with those from CMB analysis of the GC-MS data from filter samples and from the TAG semicontinuous GC-MS instrument. Also, receptor models will be applied to the high-resolution spectra to evaluate whether additional components can be retrieved, or whether the rotational ability of the identified components is reduced.

Two final field experiments are planned for this project:

(1) Local field experiments will be performed to characterize the high-resolution and TD spectra from gasoline, diesel, and meat cooking emissions. The variability of the spectra in time will be assessed, while taking care to provide realistic levels of dilution.

(2) The second experiment is the FLAME-2 campaign that will take place in May–June 2007 at the Missoula, MN Biomass Burning Chamber operated by the U.S. Department of Agriculture. The objective of this deployment is to obtain additional signatures of BBOA using the HR-ToF-AMS and the TD. During this campaign, we will use a new high time-resolution (10 Hz) mode of the AMS software to obtain rapid data and separate flaming versus smoldering emissions during stack burns.

References:

Zhang Q, Alfarra MR, Worsnop DR, Allan JD, Coe H, Canagaratna MR, Jimenez JL. Deconvolution and quantification of hydrocarbon-like and oxygenated organic aerosols based on aerosol mass spectrometry. Environmental Science & Technology 2005a;39(13):4938-4952.

Zhang Q, Worsnop DR, Canagaratna MR, Jimenez JL. Hydrocarbon-like and oxygenated organic aerosols in Pittsburgh: insights into sources and processes of organic aerosols. Atmospheric Chemistry and Physics 2005b;5(12):3289-3311.

Cottrell LD, Griffin RJ, Ziemba LD, Beckman PJ, Sive BC, Talbot RW, Jimenez JL. Submicron particles at Thompson Farm during ICARTT measured using aerosol mass spectrometry: case studies of organic and sulfate aerosol. Journal of Geophysical Research (submitted, 2007).

Zhang Q, Jimenez JL, Canagaratna MR, Allan JD, Coe H, Ulbrich I, Alfarra MR, Takami A, Middlebrook AM, Sun YL, Dzepina K, Dunlea E, Docherty K, DeCarlo PF, Salcedo D, Onasch T, Jayne JT, Miyoshi T, Shimono A, Hatakeyama S, Takegawa N, Kondo Y, Schneider J, Drewnick F, Weimer S, Demerjian K, Williams P, Bower K, Bahreini R, Cottrell L, Griffin RJ, Rautiainen J, Worsnop DR. Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically—influenced Northern Hemisphere mid-latitudes. Geophysical Research Letters (submitted, 2007).


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

Other project views: All 115 publications 31 publications in selected types All 31 journal articles
Type Citation Project Document Sources
Journal Article DeCarlo PF, Kimmel JR, Trimborn A, Northway MJ, Jayne JT, Aiken AC, Gonin M, Fuhrer K, Horvath T, Docherty KS, Worsnop DR, Jimenez JL. Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer. Analytical Chemistry 2006;78(24):8281-8289. R832161 (2006)
R832161 (2007)
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  • Abstract from PubMed
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  • Journal Article Dzepina K, Arey J, Marr LC, Worsnop DR, Salcedo D, Zhang Q, Onasch TB, Molina LT, Molina MJ, Jimenez JL. Detection of particle-phase polycyclic aromatic hydrocarbons in Mexico City using an aerosol mass spectrometer. International Journal of Mass Spectrometry 2007;263(2-3):152-170. R832161 (2006)
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  • Journal Article Kondo Y, Miyazaki Y, Takegawa N, Miyakawa T, Weber RJ, Jimenez JL, Zhang Q, Worsnop DR. Oxygenated and water-soluble organic aerosols in Tokyo. Journal of Geophysical Research-Atmospheres 2007;112(D1):D01203. R832161 (2006)
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  • Journal Article Takegawa N, Miyakawa T, Kondo Y, Jimenez JL, Zhang Q, Worsnop DR, Fukuda M. Seasonal and diurnal variations of submicron organic aerosol in Tokyo observed using the Aerodyne aerosol mass spectrometer (AMS). Journal of Geophysical Research-Atmospheres 2006;111(D11):D11206. R832161 (2005)
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  • Journal Article Zhang Q, Worsnop DR, Canagaratna MR, Jimenez JL. Hydrocarbon-like and oxygenated organic aerosols in Pittsburgh: insights into sources and processes of organic aerosols. Atmospheric Chemistry and Physics 2005;5(12):3289-3311. R832161 (2005)
    R832161 (2006)
    R832161 (2007)
    R832161 (Final)
    R831080 (Final)
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  • Journal Article Zhang Q, Alfarra MR, Worsnop DR, Allan JD, Coe H, Canagaratna MR, Jimenez JL. Deconvolution and quantification of hydrocarbon-like and oxygenated organic aerosols based on aerosol mass spectrometry. Environmental Science & Technology 2005;39(13):4938-4952. R832161 (2005)
    R832161 (2006)
    R832161 (2007)
    R832161 (Final)
    R831080 (Final)
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  • Journal Article Zhang Q, Jimenez JL, Worsnop DR, Canagaratna M. A case study of urban particle acidity and its influence on secondary organic aerosol. Environmental Science & Technology 2007;41(9):3213-3219. R832161 (2006)
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  • Supplemental Keywords:

    ambient air, tropospheric, air pollution, particulates, environmental chemistry, monitoring, carbonaceous particles, combustion aerosols, source apportionment, primary organic aerosols, secondary organic aerosols, ToF-AMS, thermal denuder,, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Environmental Engineering, particulate organic carbon, atmospheric dispersion models, atmospheric measurements, model-based analysis, time resolved apportionment, source apportionment, chemical characteristics, emissions monitoring, environmental measurement, airborne particulate matter, air quality models, air quality model, air sampling, speciation, particulate matter mass, analytical chemistry, aerodyne aerosol mass spectrometry, monitoring of organic particulate matter, modeling studies, chemical transport models, real-time monitoring, aerosol analyzers, chemical speciation sampling, particle size measurement

    Relevant Websites:

    http://cires.colorado.edu/jimenez Exit
    http://cires.colorado.edu/jimenez-group/AMSsd/ Exit
    http://cires.colorado.edu/jimenez-group/ToFAMSResources/ Exit
    http://www.engr.wisc.edu/cee/faculty/schauer_james.html Exit
    http://spot.colorado.edu/~hannigan/ Exit
    http://www.asrc.cestm.albany.edu/qz/ Exit

    Progress and Final Reports:

    Original Abstract
  • 2005 Progress Report
  • 2007 Progress Report
  • Final Report