Final Report: Using Carbohydrates as Molecular Markers to Determine the Contribution of Agricultural Soil to Ambient Fine and Course PM

EPA Grant Number: R832164
Title: Using Carbohydrates as Molecular Markers to Determine the Contribution of Agricultural Soil to Ambient Fine and Course PM
Investigators: Fraser, Matthew P.
Institution: Arizona State University - Main Campus
EPA Project Officer: Chung, Serena
Project Period: December 1, 2004 through November 30, 2007 (Extended to November 30, 2010)
Project Amount: $441,299
RFA: Source Apportionment of Particulate Matter (2004) RFA Text |  Recipients Lists
Research Category: Particulate Matter , Air Quality and Air Toxics , Air

Objective:

The overall goal of the project was to fully develop, employ, and verify a technique to quantify the contribution of agricultural soils entrained in the atmosphere to ambient fine (dp < 2.5 mm) and coarse (2.5 mm < dp < 10 mm) particulate matter (PM) through the quantification of carbohydrates (monosaccharides) present in agricultural soils. By comparison of the carbohydrate concentrations in agricultural soils to unimproved soils, differentiation of agricultural emissions from other fugitive dust sources (such as windblown dusts, unpaved road dusts, or construction dusts) will guide control strategies.

The key hypothesis that was tested in the research is that the carbohydrate species present in agricultural soils are chemically distinct from organic components in native soils as a result of soil improvements designed to raise the organic content, and thus the productivity of agricultural soil. Beyond the composition of the soils, this hypothesis dictates that these monosaccharides (simple sugars) can be used as specific molecular markers for tracking the entrainment of agricultural soils to the atmosphere. Further, with proper source characterization, analytical method development, and marker stability studies, the concentration of these carbohydrates in samples of ambient PM can be used to perform source reconciliation calculations to quantify the impact of this source on ambient fine and coarse PM levels.

The project hypothesis was tested through the following project activities:

  1. Optimization and validation an analytical procedure for the measurement of carbohydrates, including highly polar simple sugars, in agricultural soils by solvent extraction, compound derivatization and quantification by gas chromatography-mass spectrometry (GC-MS).
  2. Laboratory stability studies were conducted to confirm the atmospheric stability of carbohydrate markers for agricultural soil entrainment.
  3. Collection of samples of ambient PM10 and PM2.5, locally representative agricultural soils, and other crustal material from three distinct regions of the country and quantification of the concentrations of monosaccharides in these samples. Samples were collected from eastern Texas, western Texas and central Arizona. Regional differences between these locations was used to infer the usefulness of quantification of sugars as markers for agricultural soils writ large.
  4. Calculations of the contribution of entrainment of soils material to ambient levels of PM2.5 and PM10 using a variety of diffferent receptor modeling techniques.

Summary/Accomplishments (Outputs/Outcomes):

Project research optimized the quantification technique for carbohydrates that also allows quantification of other non-polar molecular markers based on using an isotopically labeled internal standard (D-glucose-1,2,3,4,5,6,6-d7) to monitor extraction efficiency, extraction using three 30 ml aliquots of 1:1(v/v) dichloromethane:methanol for 10 min each under mild ultrasonic agitation, followed by derivitization with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% trimethylchlorosilane (TMCS) and pyridine for 3 hrs at 70oC. The converted trimethylsilyl derivatives were analyzed by GC/MS within 24 hrs to minimize hydrolysis of the derivitized sugars. Analysis with standard GC/MS procedures was well-suited for quantification of derivitized sugars.

Stability of key sugar marker compounds was simulated in laboratory studies to evaluate the stability in aqueous solutions (simulating cloud and fog droplet chemistry) as well as on filter material exposed to gaseous oxidants. In both cases, representative sugars were found to be stable for up to 7 days (the extent of the testing period) confirming their suitability for use as markers of atmospheric transport.

Sampling of aerosols and soils in eastern Texas included collection of native soil, agricultural soil (rural locations only), and fine PM samples from three sites between November 2005 and July 2006. Of the sites, San Augustine (31o32’N, 94 o 10’W) and Clarksville (33 o 37’N, 95 o 3’W) were located in rural areas of eastern Texas, and the Dallas sampling site (32 o 49’N, 96 o 51’W) was located in the urban core of that city. Concentrations of total measured aerosol saccharides ranged from 8 to 372 ng m-3 with an average of 128 ng m-3 at Clarksville, from 15 to 355 ng m-3 with an average of 70 ng m-3 at San Augustine, and from 16 to 196 ng m-3 with an average of 52 ng m-3 at Dallas. The most prevalent saccharide was levoglucosan, followed by glucose, sucrose, and trehalose. Statistical analysis of the variability between atmospheric concentrations between rural and urban locations and between aerosol sources collected during different seasons and source attribution modeling lead to the conclusion that trehalose and sugar polyols, particularly mannitol and arabitol were emitted from a common source likely to be fungal material present in soils, sucrose and glucose are emitted from a common source likely to be representing primary biological aerosol particles such as pollen spores, and levoglucosan and glycerol are emitted from a common source assumed to be biomass combustion.

Sampling of PM2.5 was conducted between January and June, 2007, in Big Bend National Park (29o16’N, 103 o 18’W) in West Texas to characterize the contribution of saccharides and other organic material to the visibility-reducing pollution in this protected visual environment. Several important saccharide compounds including levoglucosan, glucose, sucrose, and trehalose were quantified in each sample with glucose found to be the most abundant saccharide compound, followed by levoglucosan, sucrose (elevated in May only), and small amounts of trehalose. Source attribution analysis identified three sources enriched in sugars and included biomass combustion (rich in levoglucosan), a glucose and trehalose rich aerosol source (possibly indicating bio-aerosols as glucose serves as a primary carbon reservoir for plants and microorganisms), and a sucrose rich aerosol source (possibly indicating pollen source as sucrose is important in development of flower buds and is a major constituent in pollen). Other aerosol sources identified in Big Bend National Park include crustal material (rich in aluminum and silicon), secondary particle formation (rich in sulfate), sea salt (rich in sodium), mobile sources (rich in petroleum biomarkers), and wax material (rich in alkanes).

In an effort to identify and assess the relative contribution of crustal material and biological aerosols to ambient PM in the desert southwest of the United States, and particularly to assess the contribution of soil entrainment, a series of ambient PM and soil samples was collected in Higley, AZ (33 o 18’N, 111 o 43’W), a suburb of Phoenix between January and May, 2008. Samples of both PM2.5 and PM10 were collected over a 24-hr period every other day as well as samples of native soil, agricultural soil and road dust. Saccharide composition between the analysis of PM2.5 and PM10 samples collected at the Higley site and corroborated the role of combustion related sources (i.e. biomass combustion for levoglucosan which had equal concentrations in PM2.5 and PM10) and mechanical sources of dust (i.e., glucose, sucrose, trehalose, and the sugar polyols from soil and primary biological sources, which were enriched in PM10 relative to PM2.5). Seasonal analysis showed higher levoglucosan concentrations in the winter (from home heating through wood combustion) and higher levels of glucose and sucrose in the spring (from renewed biological activity during the spring growing season). Comparison of saccharides in ambient PM to saccharides in size-selected soil resuspensions found that ambient PM was more enriched in saccharides than soil, excluding soil as the dominant source of saccharides in ambient PM.

To investigate other potential sources of aerosol saccharides, a total of 9 plant and spore samples were obtained representing vegetation and fungi common to the southwest US desert. Size selected samples representing PM2.5 and PM10 of these sources were collected and analyzed for the same saccarides as the prior soil and PM studies. There was no statistically significant difference in saccharide profiles between the PM2.5 and PM10 fraction of the collected samples, but the plant and spore samples displayed different patterns in total measured saccharide concentration and relative abundance of saccharides between the two sample categories. Excluding levoglucosan (which is dominated by biomass combustion), the primary biological aerosol particle (PABP) size-selected samples had total saccharide content ranging from 1% to 27% relative to PM mass, compared to ambient aerosols collected in Higley which contained 0.20% measured saccharides on average in PM2.5 and 0.11% in PM10 mass, and agricultural soil, native soil and road dust samples which were all less than 0.02% of PM2.5 or PM10 mass as measured saccharides. This conclusively details that primary biological aerosol particles (such as spores, pollen or abrased plant material) are the dominant sources of airborne saccharides. This directly contradicts the commonly held assumption that saccharides are indicators or resuspended soil material.

In cooperation with the Institute of Chemical Technologies and Analytics at Vienna University of Technology in Austria, ambient PM10 samples and soil samples collected in 2005 at different locations in Austria were analyzed for saccharide composition for comparison purposes. The goal of this collaboration was to compare the saccharide composition between soil samples collected in Austria and Arizona, and to compare the measurement of aerosol saccharides by two different analytical methods. Comparisons between the Austria soil samples (collected in March and April) and Higley soil samples (collected in April) show comparable saccharide contents in agricultural soils, but elevated saccharide content from the street dust collected in Austria. However, as in Arizona, the ambient PM10 collected was enriched in saccharides compared to soil and road dust samples indicating the role of direct PBAP emissions. PM10 samples collected in May and August 2005 at four sites in Austria did not show much variation in PM mass between May (23.2 ± 4.9 μg m-3) and August (23.5 ± 5.9 μg m-3), the average of total measured saccharides increased from 58 ng m-3 to 122 ng m-3 during this period. Most of the increase was due to an increase in the concentration of mannitol, arabitol, and trehalose, consistent with elevated fungal spore emissions in Austria during this period. In comparing analytical methods, slightly higher concentrations of saccharides were measured by the HPLC-based method relative to the GCMS-based method, with an overall good agreement within error ranges between the two data sets, providing independent verification of the analytical methods used in this project.

Conclusions:

The key hypothesis tested in this project, that the carbohydrate species present in agricultural soils are chemically distinct from organic components in native soils as a result of soil improvements designed to raise the organic content, and thus the productivity of agricultural soil, was verified.  However, based on the combined aerosol and soil sampling programs, we found that the key source that determines the airborne saccharide concentrations is actual direct emission of primary biological aerosol particles (PBAPs) and not entrainment of soils.  Using source sampling of primary biological materials, we found that PBAPs were as important to airborne particle concentrations as soil entrainment for PM10 during our sampling program in 2008 in Higley, AZ (outside Phoenix). 


Journal Articles on this Report : 4 Displayed | Download in RIS Format

Other project views: All 21 publications 4 publications in selected types All 4 journal articles
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Journal Article Clements AL, Fraser MP, Upadhyay N, Herckes P, Sundblom M, Lantz J, Solomon PA. Source identification of coarse particles in the Desert Southwest, USA using Positive Matrix Factorization. Atmospheric Pollution Research 2017;8(5):873-884. R832164 (Final)
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  • Journal Article Jia Y, Bhat S, Fraser MP. Characterization of saccharides and other organic compounds in fine particles and the use of saccharides to track primary biologically derived carbon sources. Atmospheric Environment 2010;44(5):724-732. R832164 (Final)
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  • Journal Article Jia Y, Clements AL, Fraser MP. Saccharide composition in atmospheric particulate matter in the southwest US and estimates of source contributions. Journal of Aerosol Science 2010;41(1):62-73. R832164 (Final)
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  • Journal Article Jia Y, Fraser M. Characterization of saccharides in size-fractionated ambient particulate matter and aerosol sources: the contribution of primary biological aerosol particles (PBAPs) and soil to ambient particulate matter. Environmental Science & Technology 2011;45(3):930-936. R832164 (Final)
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  • Supplemental Keywords:

    particulate matter source apportionment, airborne saccharides, soil entrainment, primary biological aerosol particles, RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, Environmental Monitoring, atmospheric particulate matter, chemical characteristics, airborne particulate matter, agricultural soils, molecular markers, PM, fine particulate formation

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    Original Abstract
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