Impact/Purpose:

The overall goal of the proposed project is to fully develop, employ and verify a technique to quantify the contribution of agricultural soils entrained in the atmosphere to ambient fine and coarse particulate matter (PM). The proposed research will test the hypothesis 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 productivity of agricultural soil. By comparison of the concentrations of marker species in agricultural soils to unimproved soils, it will be possible to separate agricultural emissions from other fugitive dust sources (such as windblown dusts, unpaved road dusts or construction dusts).

Description:

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 70^oC. 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 (31^o32’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 PM_2.5 was conducted between January and June, 2007, in Big Bend National Park (29^o16’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 PM_2.5 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 PM_2.5 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 PM_2.5 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 PM_2.5). 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 PM_2.5 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 PM_2.5 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 PM_2.5 and 0.11% in PM₁₀ mass, and agricultural soil, native soil and road dust samples which were all less than 0.02% of PM_2.5 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.

Record Details:

Record Type:PROJECT( ABSTRACT )

Start Date:12/01/2004

Completion Date:11/30/2007

Record ID: 113441

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Related Organizations:

Role :OWNER

Organization Name :RICE UNIVERSITY

Mailing Address :6100 S Main

Citation :Houston

State :TX

Zip Code :77005

Project Information:

Approach :

The proposed method will rely on the quantification of carbohydrates (monosaccharides) in agricultural soils to develop molecular markers specific to entrained agricultural soils. By quantifying these monosaccharides in other crustal material and in ambient PM, this project will focus on separating the contribution of agricultural sources of PM from other fugitive dusts sources. The research will expand the molecular marker technique that has been widely used to apportion ambient PM, and study the contribution of agricultural sources to PM levels in different regions of the United States.

Cost :$441,299.00

Project IDs:

ID Code :R832164

Project type :EPA Grant