Name: electrostatic method to remove particulate organic matter from soil
Uploaded: 2021-02-10T13:30:00
Description: Watch this Scientific Journal Video about Electrostatic Method to Remove Particulate Organic Matter from Soil at JoVE.com

This work was supported solely by USDA-ARS base funding. The authors greatly appreciate Mikayla Kelly, Caroline J. Melle, Alex Lasher, Emmi Klarer, and Katherine Son for their technical help.

1. Soil preparation
<ol>
	<li>Collect soil samples to the desired depth. Thoroughly dry the soil at 40 &#176;C or following lab-specific standard protocols.</li>
	<li>Sieve the soil through appropriate-sized soil sieves to obtain approximately 10-25 g of sieved soil. Many studies use a 1- or 2-mm sieve. The amount of soil is based on the mass required for the downstream analyses and will impact the number of times the electrostatic removal step will need to be repeated.</li>
	<li>Place the soil in a clean, dry metal or...

<ol>
	<li>Gosling, P., Parsons, N., Bending, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+are+the+primary+factors+controlling+the+light+fraction+and+particulate+soil+organic+matter+content+of+agricultural+soils.">What are the primary factors controlling the light fraction and particulate soil organic matter content of agricultural soils.</a> Biology and Fertility of Soils. 49 (8), 1001-1014 (2013).</li><li>Gollany, H. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soil+organic+carbon+accretion+vs.+sequestration+using+physicochemical+fractionation+and+CQESTR+simulation.">Soil organic carbon accretion vs. sequestration using physicochemical fractionation and CQESTR simulation.</a> Soil Science Society of America Journal. 77 (2), 618-629 (2013).</li><li>Cambardella, C. A., Gajda, A. M., Doran, J. W., Wienhold, B. J., Kettler, T. A., Kimble, J. M., Lal, R., Follett, R. F., Stewart, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Assessment methods for soil carbon. , 349-359 (2001).</li><li>Wander, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Soil organic matter in sustainable agriculture. , 67-102 (2004).</li><li>Curtin, D., Beare, M. H., Qiu, W., Sharp, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Does+particulate+organic+matter+fraction+meet+the+criteria+for+a+model+soil+organic+matter+pool.">Does particulate organic matter fraction meet the criteria for a model soil organic matter pool.</a> Pedosphere. 29 (2), 195-203 (2019).</li><li>Kirkby, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stable+soil+organic+matter:+A+comparison+of+C:N:P:S+ratios+in+Australian+and+other+world+soils.">Stable soil organic matter: A comparison of C:N:P:S ratios in Australian and other world soils.</a> Geoderma. 163 (3-4), 197-208 (2011).</li><li>Strickland, T. C., Sollins, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+method+for+separating+light-+and+heavy-fraction+organic+material+from+soil.">Improved method for separating light- and heavy-fraction organic material from soil.</a> Soil Science Society of America Journal. 51 (5), 1390-1393 (1987).</li><li>Golchin, A., Oades, J. M., Skjemstad, J. O., Clarke, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+of+free+and+occluded+particulate+organic+matter+in+soils+by+solid+state+13C+Cp/MAS+NMR+spectroscopy+and+scanning+electron+microscopy.">Study of free and occluded particulate organic matter in soils by solid state 13C Cp/MAS NMR spectroscopy and scanning electron microscopy.</a> Soil Research. 32 (2), 285-309 (1994).</li><li>Theodorou, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitrogen+transformations+in+particle+size+fractions+from+a+second+rotation+pine+forest+soil.">Nitrogen transformations in particle size fractions from a second rotation pine forest soil.</a> Communications in Soil Science and Plant Analysis. 21 (5-6), 407-413 (1990).</li><li>Kaiser, M., Ellerbrock, R. H., Sommer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Separation+of+coarse+organic+particles+from+bulk+surface+soil+samples+by+electrostatic+attraction.">Separation of coarse organic particles from bulk surface soil samples by electrostatic attraction.</a> Soil Science Society of America Journal. 73 (6), 2118-2130 (2009).</li><li>Kuzyakov, Y., Biriukova, O., Turyabahika, F., Stahr, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrostatic+method+to+separate+roots+from+soil.">Electrostatic method to separate roots from soil.</a> Journal of Plant Nutrition and Soil Science. 164 (5), 541 (2001).</li><li>Schneider, C. A., Rasband, W. S., Eliceiri, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NIH+Image+to+ImageJ:+25+years+of+image+analysis.">NIH Image to ImageJ: 25 years of image analysis.</a> Nature Methods. 9 (7), 671-675 (2012).</li></ol>

The electrostatic attraction method was effective in removing POM from the silt loam soils. The method described here is slightly different from Kaiser, et al.10 which used a combination of glass/cotton. We treated all but the finest soil fraction and used polystyrene rather than glass due to the triboelectric difference, which for polystyrene/nylon is 100 nC/J compared to glass/ cotton at 20 nC/J12. Glass and polystyrene foam have proven effective and convenient in more re...

Accurate estimates of soil organic carbon (SOC) are important in evaluating changes resulting from agricultural management or the environment. Particulate organic matter (POM) has important functions in the ecology and physics of a soil but it is often short lived and varies based on several factors including season, moisture conditions, aeration, sample collection techniques, recent soil management, vegetation life cycle, and others1. These temporally unstable sources can confound estimates of long-term trends in stable and truly sequestered soil organic carbon2.
Despite being well-defined, common, and important, POM is not easily separated from soil nor is it easy to measure quantitatively. Particulate organic matter has been measured as that which floats in liquids (light fraction, typically 1.4-2.2 g cm-3), or as that which can be separated by size (e.g., &#62; 53-250 &#181;m or &#62; 250 &#181;m), or a combination of the two3,4,5. Both size-based and density-based techniques can influence the quantitative and chemical outcomes of POM measurement4. A careful visual inspection of soil that has been size-fractionated using routine methods often reveals long, narrow structures like roots and slivers of leaf or stem that have passed through the screen. Simply removing these structures by hand has been shown to substantially reduce measurements of total SOC2,6 but the method is notably subject to the diligence and visual acuity of the operator. POM separation from a soil sample as the light fraction during flotation in a dense liquid7 does not capture all POM, and excessive shaking during the flotation process can actually reduce the amount of light fraction recovered from a sample8. Flotation requires many steps and exposes the soil to chemical solutions which can change the chemical characteristics or dissolve and remove constituents that may be of interest4.
Alternative methods for removing POM have been used to avoid or augment the use of dense aqueous solutions. Kirkby, et al.6 compared light fraction removal using two flotation procedures to a dry sieving/winnowing method9. Winnowing was performed by passing a light current of air across a thin layer of soil to gently lift away the light from the heavy fraction. The dry sieving/winnowing performed similarly to the two flotation methods with regard to C, N, P, and S content; however, the authors suggest that dry sieving/winnowing produced &#34;slightly cleaner&#34; soils6. POM has also been separated from soil using electrostatic attraction10,11 in which organic particles are isolated by passing an electrostatically charged surface above the soil. The electrostatic attraction method successfully recovered POM, referred to as course organic particles, from dried, sieved (&#62; 0.315 mm) soils with statistical repeatability comparable to other methods of size and density fractionation10.
Here we demonstrate how electrostatic attraction can be used to remove POM of sizes ranging from visible to microscopic. Unlike other reported methods, electrostatic attraction of fine soil also removes a small portion of mineral and aggregated soil which is visibly like the remaining soil. Given our results to date, it is reasonable to assume that the removal of a small portion of non-POM soil will have no substantial effect on the downstream analyses; however, this assumption should be verified for a specific soil if large proportions of the total soil sample are being removed electrostatically. The methods and examples provided here were performed on silt loam loess soils from a semi-arid environment.
This method may not be suitable for all soil types but has the advantages of being quick and efficient in removing particulate organic matter too small to remove manually or by an air current. Process speed is important in reducing fatigue, ensuring consistency, and encouraging greater replication for better accuracy of conclusions. Additionally, the ability to remove very small particulates is important in avoiding bias toward soils with larger rather than small particulate sizes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>brush, camel-hair</td>
			<td></td>
			<td></td>
<td></td>
		</tr>
		<tr>
			<td>petri dish, glass or plastic</td>
			<td></td>
<td></td>
<td></td>
		</tr>
		<tr>
			<td>polystyrene foam, cotton or nylon cloth</td>
<td></td>
<td></td>
<td></td>
		</tr>
		<tr>
			<td>soil</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>soil sieves</td>
			<td></td>
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			<td></td>
		</tr>
	</tbody>
</table>

electrostatic method to remove particulate organic matter from soil

Estimations of soil organic carbon are dependent on soil processing methods including removal of undecomposed plant material. Inadequate separation of roots and plant material from soil can result in highly variable carbon measurements. Methods to remove the plant material are often limited to the largest, most visible plant materials. In this manuscript we describe how electrostatic attraction can be used to remove plant material from a soil sample. An electrostatically charged surface passed close to dry soil naturally attracts both undecomposed and partially decomposed plant particles, along with a small quantity of mineral and aggregated soil. The soil sample is spread in a thin layer on a flat surface or a soil sieve. A plastic or glass Petri dish is electrostatically charged by rubbing with polystyrene foam or nylon or cotton cloth. The charged dish is passed repeatedly over the soil. The dish is then brushed clean and recharged. Re-spreading the soil and repeating the procedure eventually results in a diminishing yield of particulates. The process removes about 1 to 5% of the soil sample, and about 2 to 3 times that proportion in organic carbon. Like other particulate removal methods, the endpoint is arbitrary and not all free particulates are removed. The process takes approximately 5 min and does not require a chemical process as do density flotation methods. Electrostatic attraction consistently removes material with higher than average C concentration and C:N ratio, and much of the material can be visually identified as plant or faunal material under a microscope.

The results presented here are based on the analysis of silt loam soils from agricultural sites in the Pacific Northwest (Table 1). Soils were collected to depths of 0-20 cm or 0-30 cm, dried at 40 &#176;C, passed through a 2 mm sieve, and treated using a polystyrene surface charged with a nylon cloth.
The amount of soil electrostatically removed from a sample varied. About 1% to 6% of the total soil mass was re...

Watch this Scientific Journal Video about Electrostatic Method to Remove Particulate Organic Matter from Soil at JoVE.com

Electrostatic Method to Remove Particulate Organic Matter from Soil

Removing recently deposited and incompletely decomposed plant material from soil samples reduces the influence of temporary seasonal inputs on soil organic carbon measurements. Attraction to an electrostatically charged surface can be used to quickly remove a substantial amount of particulate organic matter.

Estimations of soil organic carbon are dependent on soil processing methods including removal of undecomposed plant material. Inadequate separation of ...

Electrostatic attraction is an efficient way to reduce particulate organic matter in a soil sample. The main advantage of this method is that requires minimal visual judgment and works on fine particles not visible to the eye. Removing undecomposed organic fragments improves accuracy and consistency in measuring long term soil carbon storage.After collecting soil samples to the desired depth, thoroughly dry them at 40 degrees Celsius. Sift the soil through appropriate sides soil sieves to obtain approximately 10 to 25 grams of sieved soil. Place the soil in a clean dry metal or a glass flat bottomed pan that is large enough for the soil to be spread thin.Gently shake the pain horizontally to distribute the soil in as thin a layer as possible. Hold a 100 mm diameter glass or a polystyrene Petri dish top or bottom in one hand and vigorously rub the outer surface with a clean piece of nylon cloth, cotton cloth or polystyrene foam several times. Perform the surface charging away from the sample.When finished, inspect the surface of the Petri dish to make sure that it is clean. Lower the charged surface to within 0.5 to 2 centimeters above the soil and move it horizontally to pick up as much particulate material as possible. Attraction to the surface can be noted visually and audibly.When the Petri dish no longer attracts additional particles, move the dish away from the sample. To clean the electrostatic surface, hold it over a collection dish and use a fine brush to transfer the electrostatically attracted material from the Petri dish surface into the collection dish. Repeat this process until the number of organic matter particles being picked up decreases.Redistribute the soil sample by horizontal shaking of the soil pan to expose new material at the surface and continue electrostatic collection. Determine the end point by visual inspection of the charged surface to determine whether a significant amount of organic particulates has been removed from the soil. This protocol was used for the analysis of silt loam soils from agricultural sites in the Pacific Northwest.About 1%to 6%of the total soil mass was removed. In all cases the proportion of total sample carbon removed was greater than the soil mass removed. The carbon concentration and carbon to nitrogen ratio of the electrostatically removed soil fraction was always greater than the remaining soil.The ambient conditions and the combination of materials used to produce the charged surface affected the results. The affects of treatment endpoints were examined by collecting a series of three electrostatic samples one after the other from the same soil sample. The first treatment collected the greatest amount of carbon.The following two treatments were still highly enriched in carbon compared to the remaining soil. Finally, the amount of particulate material that could be electrostatically removed from the fine silt-sized fraction that passed through a 53 micrometer screen was tested on five silt loan soils. The electrostatically removed fractions demonstrated very little enrichment of particulate organic matter.Microscopic inspection revealed that particulate organic matter does exist in the fine soil fraction of the soils but in very small quantities. The C to N ratio tends to stabilize as in completely decomposed organic matter is removed. This might lead to better models of long term soil organic matter.

electrostatic-method-to-remove-particulate-organic-matter-from-soil

Research

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Environment

Design and Operation of a Continuous 13C and 15N Labeling Chamber for Uniform or Differential, Metabolic and Structural, Plant Isotope Labeling

Tracing rare stable isotopes from plant material through the ecosystem provides the most sensitive information about ecosystem processes; from CO2 fluxes and soil organic matter formation to small-scale stable-isotope biomarker probing. Coupling multiple stable isotopes such as 13C with 15N, 18O or&#160;2H has the potential to reveal even more information about complex stoichiometric relationships during biogeochemical transformations. Isotope labeled plant material has been used in various studies of litter decomposition and soil organic matter formation1-4. From these and other studies, however, it has become apparent that structural components of plant material behave differently than metabolic components (i.e. leachable low molecular weight compounds) in terms of microbial utilization and long-term carbon storage5-7. The ability to study structural and metabolic components separately provides a powerful new tool for advancing the forefront of ecosystem biogeochemical studies. Here we describe a method for producing 13C and 15N labeled plant material that is either uniformly labeled throughout the plant or differentially labeled in structural and metabolic plant components.
Here, we present the construction and operation of a continuous 13C and 15N labeling chamber that can be modified to meet various research needs. Uniformly labeled plant material is produced by continuous labeling from seedling to harvest, while differential labeling is achieved by removing the growing plants from the chamber weeks prior to harvest. Representative results from growing Andropogon gerardii Kaw demonstrate the system&#39;s ability to efficiently label plant material at the targeted levels. Through this method we have produced plant material with a 4.4 atom%13C and 6.7 atom%15N uniform plant label, or material that is differentially labeled by up to 1.29 atom%13C and 0.56 atom%15N in its metabolic and structural components (hot water extractable and hot water residual components, respectively). Challenges lie in maintaining proper temperature, humidity, CO2 concentration,&#160;and light levels in an airtight 13C-CO2 atmosphere for successful plant production. This chamber description represents a useful research tool to effectively produce uniformly or differentially multi-isotope labeled plant material for use in experiments on ecosystem biogeochemical cycling.

Design and Operation of a Continuous 13C and 15N Labeling Chamber for Uniform or Differential, Metabolic and Structural, Plant Isotope Labeling

This method explains how to build and operate a continuous 13C and 15N isotope labeling chamber for uniform or differential plant tissue labeling. Representative results from metabolic and structural labeling of Andropogon gerardii are discussed.

Tracing rare stable isotopes from plant material through the ecosystem provides the most sensitive information about ecosystem processes; from CO2 fluxes ...

Assessment of Labile Organic Carbon in Soil Using Sequential Fumigation Incubation Procedures

Management practices and environmental changes can alter soil nutrient and carbon cycling. Soil labile organic carbon, a readily decomposable C pool, is highly sensitive to disturbance. It is also the primary substrate for soil microorganisms, which is fundamental to nutrient cycling. Due to these attributes, labile organic carbon (LOC) has been identified as an indicator parameter for soil health. Quantifying the turnover rate of LOC also aids in understanding changes in soil nutrient cycling processes. A sequential fumigation incubation method has been developed to estimate soil LOC and potential C turnover rate. The method requires fumigating soil samples and quantifying CO2-C respired during a 10 day incubation period over a series of fumigation-incubation cycles. Labile organic C and potential C turnover rate are then extrapolated from accumulated CO2 with a negative exponential model. Procedures for conducting this method are described.

Labile organic carbon (LOC) and the potential carbon turnover rate are sensitive indicators of changes in soil nutrient cycling processes. Details are provided for a method based on fumigating and incubating soil in a series of cycles and using the CO2 accumulated during the incubation periods to estimate these parameters.

Management practices and environmental changes can alter soil nutrient and carbon cycling. Soil labile organic carbon, a readily decomposable C pool, is ...

A Gusseted Thermogradient Table to Control Soil Temperatures for Evaluating Plant Growth and Monitoring Soil Processes

Thermogradient tables were first developed in the 1950s primarily to test seed germination over a range of temperatures simultaneously without using a series of incubators. A temperature gradient is passively established across the surface of the table between the heated and cooled ends and is lost quickly at distances above the surface. Since temperature is only controlled on the table surface, experiments are restricted to shallow containers, such as Petri dishes, placed on the table. Welding continuous aluminum vertical strips or gussets perpendicular to the surface of a table enables temperature control in depth via convective heat flow. Soil in the channels between gussets was maintained across a gradient of temperatures allowing a greater diversity of experimentation. The gusseted design was evaluated by germinating oat, lettuce, tomato, and melon seeds. Soil temperatures were monitored using individual, battery-powered dataloggers positioned across the table. LED lights installed in the lids or along the sides of the gradient table create a controlled temperature chamber where seedlings can be grown over a range of temperatures. The gusseted design enabled accurate determination of optimum temperatures for fastest germination rate and the highest percentage germination for each species. Germination information from gradient table experiments can help predict seed germination and seedling growth under the adverse soil conditions often encountered during field crop production. Temperature effects on seed germination, seedling growth, and soil ecology can be tested under controlled conditions in a laboratory using a gusseted thermogradient table.

Traditional thermogradient tables create a range of temperatures across the surface. Welding gussets perpendicular to the surface of a thermogradient table will control temperature in depth increasing possible research applications.

Thermogradient tables were first developed in the 1950s primarily to test seed germination over a range of temperatures simultaneously without using a ...

Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems

Dissolved organic matter (DOM) is a highly diverse mixture of molecules providing one of the largest sources of energy and nutrients to stream ecosystems. Yet the in situ study of DOM is difficult as the molecular complexity of the DOM pool cannot be easily reproduced for experimental purposes. Nutrient additions to streams however, have been shown to repeatedly alter the in situ and ambient DOM pool. Here we demonstrate an easily replicable field-based method for manipulating the ambient pool of DOM at the ecosystem scale. During nutrient pulse experiments changes in the concentration of both dissolved organic carbon and dissolved organic nitrogen can be examined across a wide-range of nutrient concentrations. This method allows researchers to examine the controls on the DOM pool and make inferences regarding the role and function that certain fractions of the DOM pool play within ecosystems. We advocate the use of this method as a technique to help develop a deeper understanding of DOM biogeochemistry and how it interacts with nutrients. With further development this method may help elucidate the dynamics of DOM in other ecosystems.

Understanding Dissolved Organic Matter Biogeochemistry Through In Situ Nutrient Manipulations in Stream Ecosystems

Dissolved organic matter provides an important source of energy and nutrients to stream ecosystems. Here we demonstrate a field-based method to manipulate the ambient pool of dissolved organic matter in situ through easily replicable nutrient pulses.

Dissolved organic matter (DOM) is a highly diverse mixture of molecules providing one of the largest sources of energy and nutrients to stream ecosystems. ...

A Lipid Extraction and Analysis Method for Characterizing Soil Microbes in Experiments with Many Samples

Microbial communities are important drivers and regulators of ecosystem processes. To understand how management of ecosystems may affect microbial communities, a relatively precise but effort-intensive technique to assay microbial community composition is phospholipid fatty acid (PLFA) analysis. PLFA was developed to analyze phospholipid biomarkers, which can be used as indicators of microbial biomass and the composition of broad functional groups of fungi and bacteria. It has commonly been used to compare soils under alternative plant communities, ecology, and management regimes. The PLFA method has been shown to be sensitive to detecting shifts in microbial community composition.
An alternative method, fatty acid methyl ester extraction and analysis (MIDI-FA) was developed for rapid extraction of total lipids, without separation of the phospholipid fraction, from pure cultures as a microbial identification technique. This method is rapid but is less suited for soil samples because it lacks an initial step separating soil particles and begins instead with a saponification reaction that likely produces artifacts from the background organic matter in the soil. 
This article describes a method that increases throughput while balancing effort and accuracy for extraction of lipids from the cell membranes of microorganisms for use in characterizing both total lipids and the relative abundance of indicator lipids to determine soil microbial community structure in studies with many samples. The method combines the accuracy achieved through PLFA profiling by extracting and concentrating soil lipids as a first step, and a reduction in effort by saponifying the organic material extracted and processing with the MIDI-FA method as a second step.

The article describes a method that increases throughput while balancing effort and accuracy for extraction of lipids from the cell membranes of microorganisms for use in characterizing both total lipids and the relative abundance of indicator lipids to determine soil microbial community structure in studies with many samples.

Microbial communities are important drivers and regulators of ecosystem processes. To understand how management of ecosystems may affect microbial ...

Production and Measurement of Organic Particulate Matter in a Flow Tube Reactor

Organic particulate matter (PM) is increasingly recognized as important to the Earth's climate system as well as public health in urban regions, and the production of synthetic PM for laboratory studies have become a widespread necessity. Herein, experimental protocols demonstrate approaches to produce aerosolized organic PM by &#945;-pinene ozonolysis in a flow tube reactor. Methods are described for measuring the size distributions and morphology of the aerosol particles. The video demonstrates basic operations of the flow tube reactor and related instrumentation. The first part of the video shows the procedure for preparing gas-phase reactants, ozonolysis, and production of organic PM. The second part of the video shows the procedures for determining the properties of the produced particle population. The particle number-diameter distributions show different stages of particle growth, namely condensation, coagulation, or a combination of both, depending on reaction conditions. The particle morphology is characterized by an aerosol particle mass analyzer (APM) and a scanning electron microscope (SEM). The results confirm the existence of non-spherical particles that have grown from coagulation for specific reaction conditions. The experimental results also indicate that the flow tube reactor can be used to study the physical and chemical properties of organic PM for relatively high concentrations and short time frames.

This paper describes the operation procedure for the flow tube reactor and related data collection. It shows the protocols for setting the experiments, recording data and generating the number-diameter distribution as well as the particle mass information, which gives useful information about chemical and physical properties of the organic aerosols.

Organic particulate matter (PM) is increasingly recognized as important to the Earth's climate system as well as public health in urban regions, and the ...

Production and Measurement of Organic Particulate Matter in the Harvard Environmental Chamber

The production and the evolution of atmospheric organic particulate matter (PM) are insufficiently understood for accurate simulations of atmospheric chemistry and climate. The complex production mechanisms and reaction pathways make this a challenging research topic. To address these issues, an environmental chamber, providing enough residence time and close-to-ambient concentrations of precursors for secondary organic materials, is needed. The Harvard Environmental Chamber (HEC) was built to serve this need, simulating the production of gas and particle phase species from volatile organic compounds (VOCs). The HEC has a volume of 4.7 m3 and a mean residence time of 3.4 h under typical operating conditions. It is operated as a completely mixed flow reactor (CMFR), providing the possibility of indefinite steady-state operation across days for sample collection and data analysis. The operation procedures are described in detail in this article. Several types of instrumentation are used to characterize the produced gas and particles. A High-Resolution Time-of-Fight Aerosol Mass Spectrometer (HR-ToF-AMS) is used to characterize particles. A Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) is used for gaseous analysis. Example results are presented to show the use of the environmental chamber in a wide variety of applications related to the physicochemical properties and reaction mechanisms of organic atmospheric particulate matter.

This paper describes operation procedures for the Harvard Environmental Chamber (HEC) and related instrumentation for measuring gaseous and particle species. The environmental chamber is used to produce and study secondary organic species produced from the organic precursors, especially related to atmospheric organic particulate matter.

The production and the evolution of atmospheric organic particulate matter (PM) are insufficiently understood for accurate simulations of atmospheric ...

Improving Infrared Spectroscopy Characterization of Soil Organic Matter with Spectral Subtractions

Soil organic matter (SOM) underlies numerous soil processes and functions. Fourier transform infrared (FTIR) spectroscopy detects infrared-active organic bonds that constitute the organic component of soils. However, the relatively low organic matter content of soils (commonly &#60; 5% by mass) and absorbance overlap of mineral and organic functional groups in the mid-infrared (MIR) region (4,000-400 cm-1) engenders substantial interference by dominant mineral absorbances, challenging or even preventing interpretation of spectra for SOM characterization. Spectral subtractions, a post-hoc mathematical treatment of spectra, can reduce mineral interference and enhance resolution of spectral regions corresponding to organic functional groups by mathematically removing mineral absorbances. This requires a mineral-enriched reference spectrum, which can be empirically obtained for a given soil sample by removing SOM. The mineral-enriched reference spectrum is subtracted from the original (untreated) spectrum of the soil sample to produce a spectrum representing SOM absorbances. Common SOM removal methods include high-temperature combustion (&#39;ashing&#39;) and chemical oxidation. Selection of the SOM removal method carries two considerations: (1) the amount of SOM removed, and (2) absorbance artifacts in the mineral reference spectrum and thus the resulting subtraction spectrum. These potential issues can, and should, be identified and quantified in order to avoid fallacious or biased interpretations of spectra for organic functional group composition of SOM. Following SOM removal, the resulting mineral-enriched sample is used to collect a mineral reference spectrum. Several strategies exist to perform subtractions depending on the experimental goals and sample characteristics, most notably the determination of the subtraction factor. The resulting subtraction spectrum requires careful interpretation based on the aforementioned methodology. For many soil and other environmental samples containing substantial mineral components, subtractions have strong potential to improve FTIR spectroscopic characterization of organic matter composition.

SOM underlies many soil functions and processes, but its characterization by FTIR spectroscopy is often challenged by mineral interferences. The described method can increase the utility of SOM analysis by FTIR spectroscopy by subtracting mineral interferences in soil spectra using empirically obtained mineral reference spectra.

Soil organic matter (SOM) underlies numerous soil processes and functions. Fourier transform infrared (FTIR) spectroscopy detects infrared-active organic ...

Assessing the Particulate Matter Removal Abilities of Tree Leaves

Based on the conventional cleaning methods (water cleaning (WC) + brush cleaning (BC)), this study evaluated the influence of ultrasonic cleaning (UC) on collecting various sized particulate matter (PM) retained on leaf surfaces. We further characterized the retention efficiency of leaves to various sized PM, which will help to assess the abilities of urban trees to remove PM from ambient air quantitatively. 
Taking three broadleaf tree species (Ginkgo biloba, Sophora japonica, and Salix babylonica) and two needleleaf tree species (Pinus tabuliformis and Sabina chinensis) as the research objects, leaf samples were collected 4 days (short PM retention period) and 14 days (long PM retention period) after the latest rainfall. PM retained on the leaf surfaces was collected by means of WC, BC, and UC in sequence. Then, retention efficiencies of leaves (AEleaf) to three types of the various sized PM, including easily removable PM (ERP), difficult-to-remove PM (DRP), and totally removable PM (TRP), were calculated. Only around 23%-45% of the total PM retained on leaves could be cleaned off and collected by WC. When the leaves were cleaned through WC+BC, the underestimation of the PM retention capacity of different tree species was in the range of 29%-46% for various sized PM. Almost all PM retained on leaves could be removed if UC was supplemented to WC+BC. 
In conclusion, if the UC was complemented after the conventional cleaning methods, more PM on leaf surfaces could be eluted and collected. The procedure developed in this study can be used for assessing the PM removal abilities of different tree species.

The ultrasonic cleaning method was applied to elute the particulate matter (PM) retained on leaf surfaces after PM was eluted by the conventional cleaning methods (water cleaning only or water cleaning plus brush cleaning). The methodology can help to improve the estimation accuracy for PM retention capacity of leaves.

Based on the conventional cleaning methods (water cleaning (WC) + brush cleaning (BC)), this study evaluated the influence of ultrasonic cleaning (UC) on ...

Use of Principal Components for Scaling Up Topographic Models to Map Soil Redistribution and Soil Organic Carbon

Landscape topography is a critical factor affecting soil formation and plays an important role in determining soil properties on the earth surface, as it regulates the gravity-driven soil movement induced by runoff and tillage activities. The recent application of Light Detection and Ranging (LiDAR) data holds promise for generating high spatial resolution topographic metrics that can be used to investigate soil property variability. In this study, fifteen topographic metrics derived from LiDAR data were used to investigate topographic impacts on redistribution of soil and spatial distribution of soil organic carbon (SOC). Specifically, we explored the use of topographic principal components (TPCs) for characterizing topography metrics and stepwise principal component regression (SPCR) to develop topography-based soil erosion and SOC models at site and watershed scales. Performance of SPCR models was evaluated against stepwise ordinary least square regression (SOLSR) models. Results showed that SPCR models outperformed SOLSR models in predicting soil redistribution rates and SOC density at different spatial scales. Use of TPCs removes potential collinearity between individual input variables, and dimensionality reduction by principal component analysis (PCA) diminishes the risk of overfitting the prediction models. This study proposes a new approach for modeling soil redistribution across various spatial scales. For one application, access to private lands is often limited, and the need to extrapolate findings from representative study sites to larger settings that include private lands can be important.

Landscape processes are critical components of soil formation and play important roles in determining soil properties and spatial structure in landscapes. We propose a new approach using stepwise principal component regression to predict soil redistribution and soil organic carbon across various spatial scales.

Landscape topography is a critical factor affecting soil formation and plays an important role in determining soil properties on the earth surface, as it ...