Gas chromatographic studies of soil-hydrocarbon physical interactions and soil

absorption of atmospheric nitrous oxide

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Authors Prososki, Gale Kathleen

Publisher The University of Arizona.

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GAS CHROMATOGRAPHIC STUDIES OF SOIL-HYDROCARBQN

PHYSICAL INTERACTIONS AMD SOIL ABSORPTION OF

ATMOSPHERIC NITROUS OXIDE

by

Gale Kathleen Prososki

A Thesis Submitted to the Faculty o f the

DEPARTMENT OF SOILS, WATER, AND ENGINEERING

In P artia l F u lfillm e n t o f the Requirements For the Degree of

MASTER OF SCIENCE WITH A MAJOR IN SOIL AND WATER SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 8

STATEMENT BY AUTHOR

This thesis has been submitted in p a rtia l fu lf i l lm e n t of requirements fo r an advanced degree a t The U niversity o f Arizona and is deposited in the University L ibrary to be made ava ilab le to bor­rowers under rules of the L ibrary.

B rie f quotations from th is thesis are allowable without spe­c ia l permission, provided tha t accurate acknowledgment of source is made. Requests fo r permission fo r extended quotation from or repro­duction of th is manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the in terests o f scholarship. In a ll other instances, however, permission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

. . -------------------------------------------------------------------------------------------------------------------------- I? .H. L. BOHN 7 Date

Professor of S o ils , Water and Engineering

ACKNOWLEDGMENTS

I would lik e to thank Dr. H. L. Bohn, J . Gary Eckhardt, and

Dr. J. Moyers fo r th e ir guidance and assistance, the United States

A ir Force fo r p a rtia l funding, and my parents and friends fo r th e ir

emotional support and encouragement.

TABLE OF CONTENTS

Page

LIST OF TABLES. . . . . . . . . . . . . . . . . . ............................ v

LIST OF ILLUSTRATIONS ............................... v i

ABSTRACT. . . . . . . . . . . . . . . . . . . ................... v i i

CHAPTER

1. GAS CHROMATOGRAPHIC STUDIES OF SOIL-HYDROCARBONPHYSICAL INTERACTIONS . . . . . . . . . . . . . . . . . . 1

In troduction . . . . . . . . . . . . . . . . . . . . . . 1M aterials and Methods . . . . . . . . ........................... . 6Results . . . . . . . . . . . . . . . . . . ................ . 1 101 S CU S S' 1 On e * o e e . e • » . .■ # e . e . . . . . . . 21Conclusion. ............................. 31

2. SOIL ABSORPTION OF ATMOSPHERIC NITROUS OXIDE. . . . . . . . 33

In troduction . . . . . . . . . . . . . . . . . . . . . . 33Materials and Methods . . . . . . . . .................. . . . 37Results and Discussion..................... 40Conclusion. ................... 46

APPENDIX A. RAW DATA TABLES. . . . . . . . . . . . . . . . . . . 47

APPENDIX B. CHROMATOGRAMS AND MASS SPECTRA FIGURES . . . . . . . 53

LIST OF REFERENCES. ............. .............. 63

IV

LIST OF TABLES

Table Page

1. Retention Data of Various Hydrocarbonson Gila Sandy Loam S o il. ................... 9

2. Retention Data o f Hexane on Various Soil Columns . . . . . . 10

3. Retention Data o f JP-4 Jet Fuel on GilaSandy Loam S o il. . . . . . . . ................... . . . . . . . . 19

4. Number o f Theoretical P lates, N, and HeightEquivalent to a Theoretical P late, HETP, of

.183 cm Gila Sandy Loam Soil Column UsingVarious Hydrocarbons and JP-4 Components . . . . . . . . . 22

- 5. Experimental Treatments o f Gila Sandy Loam Soiland Other Reaction Chambers in a Study of Nitrous Oxide Absorption . . . . . . . . . ....................... 38

v

LIST OF ILLUSTRATIONS

Figure

1. Log o f the Specific Retention Volume o f VariousHydrocarbons on Gila Sandy Loam Soil Columnversus the Reciprocal o f the AbsoluteTemperature o f the Column Oven. . . . . . . . . . . .

2. Log of the Specific Retention Volume o f VariousHydrocarbons on Gila Sandy Loam Soil Column versus the Number o f Carbon Atoms in the Hydrocarbon . .................... . ................ .......................

3. Log o f the Specific Retention Volume a t 15°C o f VariousHydrocarbons on Gila Sandy Loam Soil Column versusthe B o ilin g 'P o in t o f the Hydrocarbon. . . . . . . . .

4. Log o f the Specific Retention Volume o f Hexaneon Various S o il Columns versus the Reciprocalof the Absolute Temperature o f the Column Oven. . . .

5. Log of the Specific Retention Volume o f Componentso f JP-4 Jet Fuel on Gila Sandy Loam SoilColumn versus the Reciprocal of the Absolute Temperature of the Column Oven. . . . . . . . . . . .

6. Experiment 1 - - Changes in Nitrous Oxide w ith Time. . . .

7. Experiment 2 — Changes in Nitrous Oxide with Time. . . .

Page

* 12

15

16

18

20

41

43

v i

ABSTRACT

Using so il as the so lid or adsorbing phase and hydrocarbon

vapors as the adsorbed gas or sample, gas-solid chromatography pan

measure physical in te ractions o f hydrocarbons with s o ils qu ick ly ,

e a s ily , and accurate ly. The length o f re ten tion o f saturated hydro­

carbons increases w ith th e ir molecular weight or bo iling po in t. Fine-

textured so ils re ta in hydrocarbons more strong ly than coarse-textured

s o ils . Soils re ta in hydrocarbons longer i f the hydrocarbons have

s tru c tu ra l cha rac te ris tics th a t make them more l ik e ly to form weak

bonds w ith s o il. One app lica tion o f th is a b i l i t y o f so ils is to

scrub hydrocarbon vapors from waste gases. The gaseous components

are phys ica lly retained by the so il where they are subject to degrada­

tio n by so il microorganisms.

Gila sandy loam so il was wetted to d iffe re n t degrees to

determine whether i t is capable of taking up atmospheric n itrous

oxide. The atmosphere in glass reaction chambers containing the

so ils was enriched w ith N^O, and changes in NgO leve ls were measured,

using gas chromatography. Wet so ils are capable o f g rea tly reducing

NgO leve ls . Though newly wetted, dry s o ils release NgO, they also

take up NgO. Dry so ils and water showed no measurable p a rtic ip a tio n

in the cycling of NgO.

v i i

CHAPTER 1

GAS CHROMATOGRAPHIC STUDIES OF SOIL-HYDROCARBON PHYSICAL INTERACTIONS

Introduction

The in te rac tion o f hydrocarbons w ith so il surfaces has been

the subject o f many so il science and a i r p o llu tio n studies (Vanloocke,

De Borger, Voets, and Verstraete 1975): Because of i t s involvement in

photochemical smog form ation, atmospheric sc ie n tis ts are concerned

w ith increased atmospheric hydrocarbon concentration from automobile

exhaust and other combustion processes. Petroleum products such as

crude o il and natural gases are often involved in s p i l ls or leaks

d ire c tly in to the s o i l .

Vanloocke e t a l . 's (1975) review found tha t petroleum s p il ls

stunted vegetation and contaminated ground water and suggested possi­

ble remedies, Suess, Netzsch-Lehner and Nowak (1,969) estimated the

life t im e o f diesel o il to be from one to three years in s o ils .

Hoeks (1972) measured the oxidation rate o f natural gas as 14-45O

grams o f CH^/hour-meter in s o ils . E l l is and Adams (1960) reviewed

the changes in s o il m icrob io log ica l, chemical, and physical proper­

t ie s due to hydrocarbon contamination. Dobson and Wilson (1964)

measured m icrobial re sp ira tio n rates when so il was exposed to varying

quan tities o f kerosene. A group o f ERA researchers have used a

method called land farming to dispose o f o il waste where so il is

cu ltiva ted and fe r t i l iz e d to increase m icrobial growth (Snyder, Rice

and Skujins 1976). The studies show tha t so il microorganisms break

down the hydrocarbons. Adams (1959) was able to adsorb natural gas

on so il held a t -1 C. This was one of the f i r s t observations of phys­

ica l adsorption by s o ils . The fixed carbon disappeared a fte r two

weeks a t room temperature.

Although the uptake o f hydrocarbon vapors by so ils is p r i ­

m arily a ttr ib u te d to m icrobial ass im ila tion , the physical a ttra c tio n

o f these vapors to the so il surface determines the sources and sinks

fo r some atmospheric po llu tan ts . Bohn (197.2, 1977) c ited various

mechanisms related to the s im ila r uptake o f inorganic gaseous and par­

t ic u la te po llu tan ts and organic gases by s o ils . The extent of th is

uptake suggests the p o s s ib ility tha t so il is a sink fo r many atmos­

pheric po llu tan ts . Several groups have studied the ca p a b ilit ie s of

so il f i l t e r s to remove po llu ta n t gases from waste a ir (Carlson 1970;

Bohn and Miyamoto 1973). Abeles, Craker, Forrence and Leather (1971)

found tha t ethylene at ppm levels from automobile exhaust is taken Up

by s o i l . More recen tly , the uptake of n itrous oxide (Blackmer and

Bremner 1976) and su lfu r dioxide (Bremner and Banwart 1976) by so ils

has become a major course o f study. The fa te of these atmospheric

po llu tan ts needs fu rth e r investiga tion (Rasmussen, Taheri and Kabel

1975).

The degree of physical in te rac tion o f hydrocarbons w ith so il

is an important l in k in the process leading to m icrobial ass im ila tion .

The actual residence time o f a hydrocarbon in the so il is thought to

be re lated to i t s physical properties such as bo iling po in t and

molecular s tructu re .(Bohn 1977). The rate o f m icrobial assim ila tion

o f a hydrocarbon in the so il is dependent upon i t s a v a ila b il i ty ,

which is re la ted to i t s physical in te rac tion or adsorption a t the

so il surfaces.

Although s o il chemical and physical properties change when the

hydrocarbon is incorporated in to the s o il ( E l l is and Adams I960), the

physical in te rac tion o f hydrocarbons w ith the so il has not been stud­

ied. This may be due to lack o f methods to observe the s o il hydrocar­

bon in te rac tion . Most methods to measure adsorption are s ta tic and

involve so il s te r i l iz a t io n (Abeles et a l . 1971). These methods are

poor fo r measurements of so il hydrocarbons adsorption because of the

lim ited in te rac tion o f v o la t i le gaseous hydrocarbons w ith s o i l .

Gas chromatography o ffe rs a very sensitive means o f measuring

the minimal in te ractions o f certa in hydrocarbons w ith porous adsor­

bents . Butle r and Burke (1976) used gas chromatography to character­

ize the re tention capacity o f several porous polymer beads commonly

used as gas chromatographic column packing m ateria ls. Byhov,

Gerasimova, Krizhanenko and Shvetsov (1976) examined the p o s s ib ilit ie s

of applying gas chromatography to study certa in polar and non-polar

compounds on natural clay minerals o f varying c ry s ta llin e structure

and composition. The calculated heats of adsorption were compared to

conventional measurements. Okamura and Sawyer (1973) studied in te r ­

actions o f normal and halogenated hydrocarbons on s o il , s i l ic a , and

Chromosorb W when they were hydrated to d iffe re n t degrees using gas

4

chromatography. Soil re tention of normal alkanes decreased with

increased water content o f the s o i l . They concluded tha t absorption

by the water layer on the so il surface was not the dominant reten­

tion mechanism.

Gas chromatography, since i ts inception (James and Martin

1952), has become a popular method fo r accurately measuring many

thermodynamic properties such as a c t iv ity c o e ffic ie n ts , heats of

vaporiza tion , and p a rt it io n co e ffic ie n ts (Kobayashi, Chappelear and

Deans 1967). The theory of gas chromatography pertains to an equi­

lib rium d is tr ib u tio n established between a gas and so lid or high b o il­

ing point liq u id phase. This equilibrium is described by the change

in retentionn volume of a component o f the vapor phase w ith tempera­

ture. The spec ific re tention volume, Vg, is the amount of ca rr ie r gas

required to transport the vapor component through the chromatographic

column divided by the mass of the packing m a te ria l. Vg is approxi­

mately equivalent to K*. The re tention parameter, K ', is the reten­

tion volume corrected fo r the dead volume of the column and is

re lated to the p a rt it io n c o e ffic ie n t, K, by:

K = = BK' ( i . nso lid

where a ^ and aso-|1-cj are the a c t iv it ie s of component a in the gas

and liq u id phases and 3 is the ra tio of the to ta l gas volume in the

column to the volume of the sta tionary phase of adsorbent. Since 6 is

a constant, K is d ire c tly proportional to K’ . The re la tionsh ip o f K

to temperature T is defined by:

AG = RT In K

5

( 1 . 2 )

where AG is the Gibbs free energy function and R is the gas constant.

However, the use of AG in gas chromatography presents the problem of

defin ing the standard state fo r the system. James, Gidding, and

Keller (1965) discussed the thermodynamic p i t fa l ls o f gas chromatog­

raphy. Standard thermodynamic properties must be c a re fu lly defined

in order to a tta in the absolute value o f AG.

The purpose of th is study is to compare re tention volumes

rather than determine an absolute value fo r AG. Choosing a steady

state condition defines a AG' as being proportional to the free

energy. Since Vg, the spec ific re ten tion volume,is d ire c tly propor­

tiona l to K, i t is temperature dependent. The value of AH is the

slope of log Vg versus the inverse of the column temperature. The

slope is proportional to the degree o f gas in te rac tion w ith the

so lid . I f the so lid phase in the gas chromatograph is s o i l , the

slope is related to the physical adsorption of the compound of in te r ­

est by the s o i l .

M icrobial decomposition is the u ltim ate sink o f hydrocarbons

in s o ils . Hydrocarbon a v a ila b il i ty to micro-organisms is proportional

to th e ir re tention by s o i l , which is re lated to AG'. Gas chromatog­

raphy accurately measures the re la tiv e in te rac tion o f gases or vapors

w ith the s o i l , thus providing the needed information fo r fu ture

studies regarding m icrobial assim ila tion or chemical decomposition.

This technique gathers physical information to complement the

m icrobial studies conducted on compounds tha t are re la t iv e ly unreac­

tiv e or weakly reactive w ith so il surfaces.

In te res t in th is work stems from the po ten tia l of s o il to

scrub fue l vapors and other v o la t i le organic compounds from a ir .

For example, fue l vapors escape to the atmosphere from storage tanks

tha t are being f i l le d . The p o llu tio n could be elim inated by scrubbing

the displaced a ir w ith so il i f hydrocarbons are retained by s o ils .

By packing chromatographic columns with d iffe re n t so ils and

in je c tin g various hydrocarbon vapors onto the column, one can measure

Vg and calcu late AG'. Comparing these values gives valuable informa­

tio n regarding the physical re ten tion o f hydrocarbons on s o il. This

paper reports the measurements of the re tention o f various hydrocar­

bons by dry s o ils .

M aterials and Methods

For re ten tion measurements o f various hydrocarbons, a copper

tube, 0.4 cm inside diameter and 183 cm long was packed w ith a Gila

sandy loam so il under vacuum w ith constant v ib ra tio n . Glass wool

plugs a t each end o f the column were used to hold in the packing

m a te ria l. Before packing, the column was coiled in a descending

sp ira l to f i t the column oven. The packing density was approximately 3

1.8 g/cm . For the measurement o f hexane re tention by s ix s o ils ,

the so ils were packed in 0.4 cm inside diameter and 33 cm long copper

tubes. A ll columns were conditioned fo r 24 hours a t 200°C while

helium ,c a rr ie r gas flowed through the column.

A Mikro-Tek gas chromatograph equipped w ith a flame ion iza tion

detector was used fo r the analysis. Column flow of a helium ca rrie r

gas was 60-70 ml/rnin and column oven temperatures ranged from 28 to

200°C. Approximately 50 m ic ro !ite rs o f the ind iv idua l liq u id hydro­

carbon were in jected in to a 20 ml Vacutainer tube and allowed to vapor­

ize. One-half ml o f the gaseous hydrocarbons was in jected in to a 20 ml

Vacutainer tube. One m i l l i l i t e r samples of gas phase (in the

Vacutainer) were withdrawn and in jected onto the so il chromatographic

column. Small sample s iz e s .( i.e . , low hydrocarbon concentrations)

were necessary to accurately measure re tention tim e, Tr. Measure­

ments of re ten tion time over a greater than 30°C column oven tempera­

ture range were used to ca lcu late the spec ific re ten tion volume, Vg.

The appropriate temperature range fo r a p a rticu la r compound is the

temperature at which i t is eluted from the so il column in a reason­

able amount o f time and the peak is not skewed or severely broadened.

Specific re ten tion volume is computed by:

Vr = Tr x F.R. (1.3)

Vg = Vr/Ms (1.4)

where Vr is the re tention volume in ml, Tr is the re ten tion time in

minutes, F.R. is the flow rate of c a rr ie r gas in ml/rnin, and Ms is

the mass of so il packed in the column in grams. The p lo t o f log Vg

versus the reciprocal of absolute temperature o f the column should be

lin e a r. Least squares analysis calculates a slope, which is AH ,

and the co rre la tion co e ffic ie n t of the lin e . Extrapolation or

8

in te rpo la tio n to a given temperature gives the Vg a t tha t temperature.

As the range o f experimental temperatures deviates fu rth e r from the

extrapolated temperature, the calculated Vg becomes less accurate.

Vg was calculated a t 15°C, which is a typ ica l so il temperature at

1 meter depth, and a t 100°C.

The r e l ia b i l i t y and v a lid ity o f the re tention tim es,Tr, were

measured by a sample size study. D iffe re n t concentrations o f the

organic vapor, ranging from 50 ppm to saturated vapor, were in jected

onto the so il column to observe th e ir e ffe c t on peak shape and reten­

tio n tim e. The sample sizes used throughout the study were found to

give reasonably symmetrical peaks tha t were easily detected.

To characterize hydrocarbon reactions w ith s o ils , the com­

pounds lis te d in Table 1 were in jected onto a column packed with Gila

sandy loam s o i l . To measure the hydrocarbon adsorption by d iffe re n t

s o ils , hexane was in jected onto columns packed w ith the so ils lis te d

in Table 2.

The studies above were made w ith single compounds. The je t

engine fu e l, JP-4 is an example o f a complex mixture o f organic com­

pounds . JP-4 was in jected onto the 183 cm Gila sandy loam column,

which separated the fue l better than the 33 cm column. Six d is t in c t

peaks appeared over a 28 to 150°C temperature range. Additional

peaks tha t appeared a t temperatures greater than 150°C could not be

accurately measured due to severe broadening and small peaks' heights.

The re tention time fo r each peak was measured over a greater than

30°C temperature range.

9

Table 1. Retention Data of Various Hydrocarbons on Gila Sandy Loam Soil

Compound

BoilingPoint(°c)

log Vg at

15°C 100°C SlopeIn te r­cept

methane -161 0.072 0.072 — —

ethane - 88 0.353 -0.045 0.524 - 1.46

propane - 42 0.955 0.044 1.20 - 3.19

butane - 0.5 -1.46 0.457 1.31 - 3.09

hexane 36 3.94 1.69 2.97 - 6.32

heptane 69 4.05 2.00 2.71 - 5.33

octane 126 5.29 2.63 3.50 - 6.83

ethylene -104 0.585 -0.063 0.853 - 2.37

acetylene - 84 1.22 0.106 1.46 - 3.84

cyclohexane 81 3.32 1.34 2.60 - 5.68

isobutylene - 6 3.31 1.30 2.64 - 5.82

iso-octane 116 4.87 2.20 3.51 - 7.27

pentene 30 4.44 1.87 3.38 - 7.26

toluene 111 9.69 4.36 7.01 -14.56

benzene 80 5.75 2.98 3.46 - 6.31

methanol 32 >10 >10 — - — -

acetone 58 >10 >10 — — - —

ethyl ether 74 >10 >10 — —

10

Table 2. Retention Data o f Hexane on Various Soil Columns

%log Vg

In te r­Soil Clay Texture 15°C 100°C Slope cept

Kalkaska 5 sand 1.84 .19 2.08 -5.39

Gila 10 sandy loam 3.68 1.49 2.83 -6.12

Gila 18 fin e sandy loam

4.71 1.88 3.58 -7.72

Moha11 30 sandy clay loam

4.32 2.23 2.65 -4.86

Fanno 47 clay 4.95 2.31 3.34 -6.64

Davidson* 61 clay — — — — — • — —

* no flow through th is column

11

The composition o f JP-4 was measured by mass spectrometry in

order to id e n tify the various gas chromatographic peaks. The mass

spectra were determined by a Hewlett-Packard gas chromatograph-mass

spectrometer.

Results

Table 1 shows re tention data o f various hydrocarbons adsorbed

by the column o f G ila sandy loam s o il. Retention by the s o il increases

with molecular weight,, bond unsaturation, and oxygenation o f the hydro-

carbons. When p lo tted as log Vg versus (1/TK) x 10 (Figure la - c ) ,

the data were lin e a r w ith co rre la tion coe ffic ie n ts greater than 0.96.

Raw data can be found in Table A-l in Appendix A. The spec ific

re tention increases w ith decreasing temperature. The- slope of the

lines is AH and is proportional to the p a rt it io n c o e ffic ie n t or the

temperature e ffe c t on adsorption by the Gila s o i l . Table 1 1is ts the

slope and in te rcep t o f these 1ines. The si ope also increases w ith

molecular weight, bond unsaturation, or oxygenation o f the organic

compounds.

The values o f Vg extrapolated to 15°C, a typ ica l so il tempera­

ture, and 100°C, a standard reference temperature,, and the bo iling

point of each o f the hydrocarbons are also given in Table 1. Reten­

tio n is higher a t 15°C and also increases w ith molecular weight and

number o f unsatitrated bonds.

,Figure 2 shows the re la tionsh ip o f log Vg a t 15° and 100°C

to carbon number. For compounds o f the same number o f carbon atoms,

re tention increased with degree of bond unsaturation. Figure 3

11 -

D-Butane I-Acetylene

i .n . C-Propane H-Ethylene B-Ethane

09

08

0-7

05

04

0 3

0-2

3 0 323 1 3429 3 32-8272-6

Figure la . Log of the Specific Retention Volume o f VariousHydrocarbons on Gila Sandy Loam Soil Column versus the Reciprocal o f the Absolute Temperature of the Column Oven

og

Vg

13

12M-Pentene E-Hexane J-Cyclohexane K-Isobutylene

1 0 -

0-9

0-8

0-6

0-5

0-4

0-32-3 2-4 2-5 2-6

Figure lb (continued)

14

1-0

0-9

07

06

L-Iso-octane F-Heptane G-Octane O-Toluene N-Benzene

0 5

0-4

2-2 2-4

Figure 1c (continued)

°g

Vg

6 »

5 -

A-MethaneB-EthaneC-PropaneD-ButaneE-HexaneF-HeptaneG-OctaneH-EthyleneI-AcetyleneJ-CyclohexaneK-IsobutyleneL-Iso-octaneM-PenteneN-Benzene

N

CARBON NUMBER

Figure 2. Log of the Specific Retention Volume of Various Hydrocarbons on Gila Sandy Loam Soil versus the Number of Carbon Atoms in the Hydrocarbon

og

Vg

16

m - A-Methane10h B-Ethane O

C-Propane D-Butane E-Hexane F-Heptane G-Octane H-Ethylene I-Acetylene J-Cyclohexane K-Isobutylene L-Iso-octane M-Pentene N-Benzene0-Toluene N

6- 5 h /

/M /

E A /

sy' J

yy

/y

A

yyy

yy

-166 -133 -100 -66 -33 0 33 66 100 133b o i l i n g p o i n t t ° c

Figure 3. Log o f the Specific Retention Volume a t 15°C ofVarious Hydrocarbons on Gila Sany Loam Soil Column versus the Boiling Point o f the Hydrocarbon

17

shows the re la tionsh ip between log Vg at 15°C and bo iling point of

the hydrocarbon where re tention increases with bo iling po in t.

Branched chain hydrocarbons, tha t have a lower bo iling point than

s tra ig h t chain hydrocarbons with the same number of carbons, are

retained less strong ly. Unsaturated hydrocarbons are retained more

strong ly. Retention increases w ith carbon number, bo iling po in t,

and number of unsaturated bonds. Oxygenated compounds were retained

longer than could be accurately determined under these conditions

(Table 1).

Six so ils were compared fo r hydrocarbon adsorption using

hexane as the common hydrocarbon. Table 2 l is t s re ten tion data along

with texture and percentage of clay of the s o il. Plots of log Vg3

versus (1/T K) x 10 are shown in Figure 4, and raw data can be

found in Table A-2 in Appendix A. Slopes and re tention increased with

clay content.

Table 3 gives re tention data o f the JP-4 je t fue l components

tha t were separated on the Gila sandy loam so il column. Lines3

obtained by p lo ttin g log Vg versus (1/T K) x 10 , shown in Figure 5,

have co rre la tion coe ffic ie n ts greater than 0.98. Raw data can be

found in Table A-3 of Appendix A. A sample gas chromatogram is

shown in Figure B-l in Appendix B. Only peak F had a Vg and slope

s im ila r to a pure compound previously measured. Peak F is cyclo-

hexane. Other hydrocarbons tested were not s im ila r to any of the JP-4

peaks obtained. Mass spectra were taken to attempt fu rth e r id e n t i f i ­

cation. A reconstructed chromatogram and mass spectra of peaks on

18

2-2 K-Kal kaska G-Gila Sandy Loam S-Gila Fine Sandy Loam F-Fanno M-Mohal12 0

1-8

1-6

1-4

10

0-8

0-6

0 4

3-23128 2-923 2 5 3-024 26 27

Figure 4. Log o f the Spec if ic Retention Volume o f Hexane on Various Soil Columns versus the Reciprocal of the Absolute Temperature o f the Column Oven

19

Table 3. Retention Data o f JP-4 Jet Fuel on Gila Sandy Loam Soil

l og Vg

Peak_______ Slope In tercept at 15°C a t 100°C

A 0.834 -2.09 0.80 0.158

B 1.44 -3.54 1.46 .322

C 1.66 -3.96 1.78 0.521

D 1.86 -4.21 2.23 0.815

E 2.26 -5.02 2.78 1.07

F 2.50 -5.36 3.28 1.38

20

A-Peak A B-Peak B C-Peak C D-Peak D E-Peak E F-Peak F1-0

09

08 "

06 •

05 "

04 -

03 •

27 2824 25 26 29 3-0 3-1 3-2(1/T K) x 103

Figure 5. Log o f the S pec if ic Retention Volume o f Components o f JP-4 Jet Fuel on Gila Sandy Loam Soil Column versus the Reciprocal o f the Absolute Temperature o f the Column Oven

21

the chromatogram are shown in Appendix B in Figures B-2 through B-9.

The possible id e n tity o f each peak is given on i t s spectrum.

Table 4 l is t s the number o f theore tica l p la tes, N, and height

equivalent to a theore tica l p la te , HETP, as calculated from some of

the hydrocarbon and JP-4 chromatograms. These values numerically

express the e ffic ie n cy o f the Gila sandy loam s o il column fo r separa­

tio n of a mixture o f compounds in to the ind iv idua l compounds. A

column more ty p ic a lly used fo r chromatographic separations might have

a N value in the thousands.

Discussion

The re tention o f a gas or vapor on a sol id adsorbent such as

so il can be advantageously studied by gas chromatography. The d is t r i ­

bution c o e ffic ie n t, K, o f a species between two phases, is related to

Vg in a chromatographic system (James et a l . 1965). Some thermo-<

dynamic properties are obtained wholly or in part by d iffe re n tia t io n

o f In K w ith respect to temperature. In a gas chromatographic column,

a state c lose ly approximating equilib rium ex is ts . Though the

standard state cannot be defined because a c t iv it ie s cannot be defined,

a reference state tha t c losely approximates the standard state ex is ts .

Relative free energy changes can be established th a t characterize the

re tention reaction. Studying the re tention of an organic vapor on

so il is a useful and p ractica l app lica tion of th is technique.

This technique is quick and simple. A fte r c a re fu lly packing

a chromatographic column with a s o i l , i t is inserted in the column

oven and samples are in jected onto i t . Increasing the flow rate o f

22

Table 4. Number of Theoretical Plates, N, and Height Equivalent to a Theoretical P late, HETP, o f 183 cm Gila Sandy Loam Soil Column Using Various Hydrocarbons and.JP-4 Components

Compound N HETP (cm)

methane 89 2.1

ethane 47 4.1

propane 25 7.4

butane 9.2 20

hexane 36 5.1

heptane 37 4.9

ethylene 26 7.2

acetylene 23 8.0

isobutylene 23 8.0

cyclehexane 55 3.3

iso-octane 34 5.4

JP-4 components:

peak A 60 3.3

peak B 43 4.5

peak C 32 6,9

peak D 42 5.4

peak E. 22 8.9

peak F 39 5,6

average . 40 5.4

c a rr ie r gas and the temperature decreases the re tention time; many

d iffe re n t organic compounds can be compared in a re la t iv e ly short

time. Though a gas chromatographic system is expensive, there are few

additional costs ( i . e . , ca rr ie r gas, tubing, swage-1 ok f i t t in g s , and

pure compounds).

The flame ion iza tion detector is re la t iv e ly stable and capable

o f detecting very small concentrations of a hydrocarbon, so minute

in te ractions may be evaluated. High re p ro d u c ib ility and low measure­

ment e rro r make gas chromatography accurate. Samples must be in jected

id e n tic a lly each time or e rro r w i l l be introduced in to the measurement.

The concentration o f the hydrocarbon must be large enough to

be detected, but small enough to e lu te as a symmetrical peak. When

concentrations are too high, the sta tionary phase o f so il becomes

loaded and peaks are skewed w ith a t r a i l in g t a i l . Peak broadening

occurs when temperatures are too low to elute peaks qu ick ly . Devia­

tions from symmetrical peaks introduce e rro r in to the re tention time

measurements.

Some e rro r is introduced when Vg is extrapolated to a spec ific

temperature. The accuracy of Vg versus carbon number (Figure 2) at

100°C is be tte r than a t 15°C because more o f the experimental tempera­

ture ranges include or approach 100°C; more o f the values of Vg a t

100°C were determined experimentally while a t 15°C they were deter­

mined by ca lcu la tion . Even i f the column oven could be cooled below

28°C in order to get d ire c t measurements o f Vg a t 15°C, the heavier

hydrocarbons would take an inconvenient amount o f time to be eluted

24

from the column and possibly may not be eluted. I f two re tention

mechanisms tha t dominated a t d iffe re n t temperature ranges were

involved, two slopes or A H values would apply to the re tention reac­

t io n . Extrapolated Vg's would be inaccurate i f the wrong slope or

A H was used to ca lcu la te i t .

The conditions w ith in the column are not iden tica l to the s o i l 's

natural s ta te . Water, microorganisms, and organic matter are g rea tly

reduced, allowing the mineral fra c tio n o f the so il to be studied

separately. Temperatures are mostly in excess o f normal so il tempera­

tures except fo r some high surface temperatures. Competition o f the

hydrocarbon w ith water fo r the mineral surface is elim inated by the

high operational temperatures. Okamura and Sawyer (1973) studied

re tention of some alkanes on so il hydrated to d if fe re n t degrees and

found tha t the hydrocarbon in te rac tion decreased as the so il became

hydrated, but re ten tion on dry so il was great. The re ten tion mechanism

should be studied in re la tio n to dry s o ils because dry so ils seem,to

be capable o f greater hydrocarbon re ten tion . The influence o f micro­

organisms, whose in te rac tion w ith hydrocarbons is s ig n if ic a n t

( E l l is and Adams 1960), is also minimized by high temperatures (200°C)

during conditioning and the short duration of hydrocarbon in the so il

column. Reactions w ith the organic fra c tio n may not be to ta l ly

elim inated, but a major portion of the organics are v o la tiliz e d during

the conditioning o f the column. Soil organic matter has many charged

s ites and would be l ik e ly to be involved in bonding mechanisms.

Larger diameter (5-10 cm) columns are often used to study e lu ­

tio n o f water, heavy metals, and other ions from s o il. Large diameters

contribute to ease o f packing and g rea tly reduce channeling where large

p a rtic le s s i f t in to the center and smaller p a rtic les are squeezed to

the periphery. In gas chromatographic techniques, channeling would

cause gas molecules to move s w if t ly through the so il column with

minimum chance to in te ra c t w ith the so il p a rtic le s . The tra d it io n a l

small diameter (3 mm) o f gas chromatographic columns increases the

accuracy o f the re tention volume measurement, increases the e ffic ien cy

o f the column, and provides more opportunity fo r in te rac tions .

Chromatographers prefer to use columns tha t are approximately

e ight times the diameter o f the p a rtic le s . Id e a lly , p a rtic les of

uniform size are used. This reduces channeling, y ie lds a reasonable

pressure drop across the column, and gives symmetrical, peak shape.

Only f in e sand would be used in th is case, and they would not be

representative o f natural so il and i t s a b i l i t ie s to adsorb hydrocar­

bons. Though clay p a rtic le s r e s tr ic t flow through the column, the

so ils were not sieved in order to represent the natural p a rtic le d is ­

t r ib u t io n , and because clay is the reactive surface involved in reten­

tio n of many ions by so il and seems to be the major reactive surface

in hydrocarbon re ten tion .

Fine-textured s o ils are unsuitable fo r th is technique because

gas flow through the so il column is lim ite d . The Davidson s o i l , .

where column flow could not be detected, has 61% clay and 20% s i l t .

26

These p a rtic le s are a l l greater than 300 mesh size and would not

normally be used as chromatographic packing.

E ffic iency of the column, in terms o f separating d iffe re n t

gases, is greatest when the number o f theore tica l p la tes, N, is high­

est and packing is most e f f ic ie n t . For the Gila so il column. Table 4

shows an average N o f 40 and an average HETP, height equivalent to a

theore tica l p la te , o f 5.4 cm. This column is not e f f ic ie n t and would

not be useful to separate c lose ly re lated or s im ila r ly retained com­

pounds.

This technique can fa c i l i ta te re ten tion studies o f many

compounds by s o ils . The adsorption o f atmospheric pa rticu la tes may be

determined. One can determine the so il in te ractions w ith other ;

compounds such as pestic ides. High pressure liq u id chromatography

may be used to study so il in te ractions w ith liq u id s such as o i ls .

The technique would not work to study so il in te ractions w ith v o la t i le

Compounds tha t react e ith e r too slowly or ir re v e rs ib ly . The study of

clay so ils would require high pressure lines and regulators designed

fo r safe and accurate high pressure de live ry o f the c a rr ie r gas.

In je c tion ports could not be used, but sampling valves could be

substitu ted . ,

The resu lts o f th is study provide ins igh t in to the various

mechanisms o f physical in te rac tion between so il and hydrocarbons which

d if fe r s ig n if ic a n tly when comparing the re la tiv e re ten tion o f hydro­

carbons on the so il columns. The homologous series o f normal alkanes,

s ta rtin g w ith methane and ending w ith octane, shows a marked

27

d ifference in Vg versus 1/T slopes or AH , Calculated values o f Vg

were extrapolated to 15°CS a typ ica l so il temperature in Arizona at

one meter depth; 1G0°C was in the temperature range over which the

adsorption was studied and is a useful standard in comparing experi­

mental e rro r and consistency. Slope and Vg values show an increase as

the chain length and bo iling point increase. Van der Waals forces

increase w ith size o f chain length so bo iling po in t increases. Since

van der Waals forces increase w ith s ize , large molecules would have

more a ttra c tin g forces, explaining th e ir longer re te n tio n . Figure 2

shows th is trend by p lo tt in g log Vg a t both 15 and 100°C versus carbon

number. The re la tionsh ip is more accurate at 100°C because there is

less e rro r in Vg values; more o f Vg values a t 100°C are experimental

and not calculated. Figure 3 p lo ts log Vg a t 15°C versus bo iling

po in t. This p a rtit io n in g e ffe c t may be due to the tendency o f com­

pounds to vaporize from a surface a fte r condensation, and is less fo r

compounds w ith a high b o ilin g po in t or more van der Waals forces.

Compounds w ith a high bo iling point would have a low vapor pressure

at 15°C and would tend to stay adsorbed on the so lid so il surface.

The branched hydrocarbons interacted less w ith the so il when

compared to s tra ig h t chains of the same carbon number. This may be

seen by comparing octane and iso-octane. Iso-octane has a lower

b o ilin g point than octane.

The p lo t of log Vg versus 1/T fo r methane was not possible on

the so il column because the change o f Vg w ith temperature was not mea­

surable. However, when compared w ith a ir , methane is found to be

28 ^

s lig h t ly retained. A longer column or temperatures below 28°C are

necessary to characterize the re ten tion o f methane on G ila s o il.

The order of re tention o f six-carbon hydrocarbons was

cyclohexane<n-hexane<benzene (Figure 3). This trend does not fo llow

a p a rtit io n in g e ffe c t due to bo iling p o in t, but is a function o f

s tru c tu ra l cha rac te ris tics . Cyclohexane is retained less than

n-hexane due to i t s ring structure and lower bo iling po in t. Benzene,

which is also c y c lic , is retained more than cyelohexane due to i ts

unsaturation. Saturated bonds have only sigma electrons tha t are less

d iffu se than the pi electrons tha t are also involved in unsaturated

bonds. Pi electrons are more d iffu se and read ily involved in other

bonds. Toluene, an unsaturated ring s tructu re , is retained longer

than heptane, a saturated s tra ig h t chain.

The re ten tion o f the two-carbon molecules was ethane<ethylene<

acetylene. These compounds d if fe r in the degree o f saturation o f the

carbon-carbon bond: ethane contains a s ing le bond which has one sigma

o rb ita l, ethylene a double bond which has one sigma o rb ita l and one

pi o rb ita l, and acetylene a t r ip le bond which has one sigma o rb ita l

and two pi o rb ita ls . Their bo iling poin ts.are w ith in 20°C o f each

other and they are a l l gases a t room temperature, but re tention

increases w ith number o f pi e lectrons. Iso-Butylene is branched and

has a Tower bo iling point than butane, but because o f the double

bond i t is retained longer than butane. . Although the bo iling po in t

o f a compound is important, the e ffe c t o f an unsaturated bond is

overrid ing .

29

Polar and/or oxygenated compounds such as methanol, acetone

and ethyl ether were also studied. Their re tention volumes were very

high ( log Vg>l0) and beyond the l im i t o f accurate measurement by th is

experimental set-up. Very high temperatures would be needed to

increase the k in e tic a c t iv ity of the molecule and permit i t to break

the re ta in ing bond. The strong a ttra c tio n o f s o il fo r polar compounds

may be a ttr ib u te d to the a b i l i t y of these compounds to form hydrogen

and other weak bonds w ith the s o il surface as a re s u lt o f d ipo le-

dipole a ttra c tio n s .

Table 2 shows the re tention o f hexane on several d iffe re n t

s o il columns. Although the co rre la tion was not s ta t is t ic a l ly s ig n i f i ­

cant, fin e r-te x tu re d s o ils retained the hexane longer. Clay p a rtic le s

have a net negative charge, often p o s itiv e ly charged s ite s , and are

responsible fo r the re ten tion o f many other species such as cations

and p lant n u trien ts . Since the other species capable o f appreciable

re ten tion , organic m atter, was present in low amounts, i t is l ik e ly

tha t the in te rac tion is w ith the clay surfaces.

Six peaks are separated from the JP-4 vapor w ith in the 28 to

150°C temperature range. Comparison to data fo r known hydrocarbons

shows tha t peak F is cyclohexane and other peaks are not any of the

compounds tested. Mass spectra were obtained fo r each peak separated

and detected on the gas chromatograph-mass spectrometer. Because the

mass spectrometer detects a l l compounds separated and not ju s t hydro­

carbons, as the gas chromatograph-f1ame ion iza tion detector does,

co rre la ting the mass spectrometer peaks d ire c tly w ith the A through F

30

peaks o f the gas chromatograph is not v a lid . The suspected id e n tity

o f each peak is noted on i ts spectrum in Appendix B (Figures B-2 to

B-9). Mass spectrometer id e n tif ic a t io n is not f in a l and is normally

supplemented by other id e n tif ic a tio n data such as nuclear magnetic

resonance and in fra red spectra.

The major part o f JP-4, je t fu e l, vapors could be scrubbed in

s o il , which has a good capacity to re ta in hydrocarbons. I f JP-4

vapors were pumped in to the so il to be scrubbed, peaks E and F are

not l ik e ly to escape due to th e ir f a i r ly high re ten tion . Since peak

F is cyclohexane, one could measure cyclohexane to monitor those

vapors th a t escape. Peaks A-D are more l ik e ly to escape and cause

p o llu tio n problems. These compounds are 1igh te r than cyclohexane w ith

log Vg less than cyclohexane1s , but they are very minor constituents

o f JP-4. Major components o f JP-4 include some o f the heavier hydro­

carbons such as heptane, iso-octane, toluene, benzene, and methyl

cyclohexane.

Leakage o f the gases from the so il f i l t e r may occur a t f i r s t

because the m icrobial population is not extensive enough to assim ilate

a ll o f the hydrocarbons. Once a healthy and extensive microbial

population becomes established a t the s ite o f scrubbing, i t w il l use

the retained hydrocarbons as a carbon source, making the s ites a v a il­

able to re ta in additiona l hydrocarbons. In th is way the capacity o f

the so il to re ta in the vapors is constantly renewed.

31

Conclusion

Gas chromatography is a quick, easy, and accurate technique

to study the re tention o f hydrocarbons on dry s o ils . Although the- i ,

so il is not in i t s natural s ta te , i t is possible to study the physi­

cal adsorption mechanisms separately from the b io log ica l absorption

or s o lu b il i ty in water. Measurements of re tention volume over a range

o f temperatures y ie ld a re la tiv e parameter, AG1, th a t characterizes

the adsorption reaction. Extrapolation to so il temperatures gives a

re ten tion value fo r the so il in i t s natural temperature condition.

Soil chromatographic columns are not very e f f ic ie n t fo r more usual

chromatographic work and would not be useful fo r separation of

s im ila r ly retained compounds. A reason fo r low e ffic ie n cy is due to

the large range of p a rtic le sizes in natural s o ils .

Van der Waals forces increase with size of the hydrocarbon

resu lting in a higher bo iling po in t and increased re te n tio n . Branched

isomers tested had lower bo iling points and re tention than the

s tra ig h t chains of the same number o f carbon atoms.

Unsaturated bonds have pi e lectrons; pi electrons may be more

read ily involved in other bonds. Unsaturation and number of pi

electrons increase the re tention o f the hydrocarbon. The e ffe c t of

unsaturation is more important than bo iling point in determining the

re tention o f a hydrocarbon. Oxygenated hydrocarbons are polar and

have the a b i l i t y to form hydrogen or other weak bonds. Though these

compounds may have a low bo iling po in t and are saturated, they are very

strongly reta ined. The a b i l i t y of a so il to re ta in a hydrocarbon

increases w ith f in e r textu re .

CHAPTER 2

SOIL ABSORPTION OF ATMOSPHERIC NITROUS OXIDE

In troduction

Nitrous oxide is believed to e f fe c t atmospheric ozone content

due to i t s formation o f n i t r i c oxide in the stratosphere by reacting

w ith excited oxygen atoms:

N20 + 0( 'D) = 2N0 (2.1)

N i t r ic oxides c a ta ly t ic a l ly destroy ozone (Crutzen 1976) by:

NO + 03 = N02 + 02 (2.2)

N02 + 0 = NO + 02 (2.3)

Equation (2.3) regenerates the n i t r i c oxide, so a small amount of NO

can destroy large amounts o f ozone. As s tra tospheric ozone concen­

t ra t io n s decrease, more u l t r a v io le t ra d ia t io n can reach the earth 's

surface and harmful e ffec ts to l i v in g organisms and c lim ate are

l i k e ly to occur.

Because of i t s p a r t ic ip a t io n in ozone des truc t io n , the various

sources and sinks o f n itrous oxide and i t s geochemical cyc ling are

under curren t in ve s t ig a t io n . Soil s c ie n t is ts became concerned when

i t was found th a t increased nitrogen f ix a t io n through the use of

n itrogen f e r t i l i z e r s was increasing N2 O losses from the so il

33

34

(Council on A g r icu ltu ra l Science and Technology (CAST) 1976; Rice and

Sze 1976; Sze and Rice 1976; L iu , Cicerone, Donahue, and Chameides

1976; Crutzen and Ehhalt 1977). Nitrogen f ix a t io n , the conversion o f

atmospheric to organic and inorganic nitrogen compounds, leads

in d i r e c t ly to increased n itrous oxide release to the atmosphere (CAST

1976). N itrous oxide is given o f f by the so i l in what is thought to

be the major source during the processes o f n i t r i f i c a t i o n and

d e n i t r i f i c a t io n (Cady and Bartholomew 1963; Nelson and Bremner 1970).

Yoshida and Alexander (1970) found th a t f^O was released from so il

under aerobic conditions during the n i t r i f i c a t i o n process, the micro­

b io log ica l conversion o f ammonium to n i t r i t e and n i t r a te . In

d e n i t r i f i c a t io n , fa c u l ta t iv e anaerobic bacteria use n i t r a te as an

e lectron acceptor when no oxygen is a va ila b le , reducing the n i t ra te

to Ng and N£0 . Many fac to rs in fluence the ra te o f d e n i t r i f i c a t io n

and the f^/N^O r a t io (Burford and Bremner 1975). S l ig h t ly aerobic

cond it ions, high i n i t i a l n i t r a te concentration, and lower pH favor

the production o f a la rg e r percentage o f n itrous oxide, but the ra te

o f d e n i t r i f i c a t io n is r e la t iv e ly low under these cond it ions. Although

l im ite d data are ava ilab le on the f lu x o f I^O from s o i ls (Focht 1974),

several estimates o f global evo lu tion from so il have been made (CAST

1976; Hahn, 1974; Hahn and Junge 1977). These estimates are question­

able because they are extrapolated from data of very sp e c if ic

conditions and are based on questionable assumptions, such as the

N2 /N 2 O ra t io in d e n i t r i f i c a t io n being 16. The fa c t th a t NgO released

in to a closed atmosphere during d e n i t r i f i c a t io n is reduced to Ng,

35

has been ignored because the studies were designed to demonstrate

N̂ O release during d e n i t r i f i c a t io n . The NgO losses from so il may be

less than o r ig in a l ly thought (Bremner in press).

Soil is only one source o f N̂ O in the environment. Smaller

amounts are created in combustion processes (Weiss and Craig 1976)

and by l ig h tn in g (Z ip f and Dubin 1976). The ro le o f oceans in I^O's

cyc ling is unresolved.. Hahn's group (Hahn 1974; Hahn and Junge 1977)

found oceans to be a major source o f N^O; McElroy, E lk ins , Wofsy,

and Ying (1976) believe oceans to be a sink fo r ^ 0 .

The only sink fo r N̂ O known a t th is time is photo lys is reac­

t ions in the stratosphere such as:

hvN20 = N2 + 0 (2.4)

N20 + O(D') = N2 + 02 (2.5)

and by equation (2 .1 ) . The nature and effectiveness o f global sources

and sinks is uncertain (Hahn and Junge 1977).

Not only is there a need to fu r th e r characterize losses of

N20 from s o i l , but the p o s s ib i l i t y o f so i l acting as a sink fo r

atmospheric NgO needs in ve s t ig a t io n . Several so i l microorganisms

have the capacity to reduce NgO to N2 (Delwiche 1959; Payne 1973).

Blackmer and Bremner (1976) showed th a t so i l has a s ig n i f ic a n t

capacity to m ic ro b ia l ly reduce N20 to N2. The capacity o f several

Iowa surface s o i ls to absorb N20 was greater than th e i r capacity to

36

release i t ; s o i ls continue to remove ^ 0 below ambient leve ls . The

s o i ls were moist, under anaerobic cond it ions, and th e i r capacity to

reduce ^ 0 increased as the organic matter content increased.

Increased n i t r a te leve ls decreased the s o i l ' s f^O reducing c a p a b i l i ty

(Blackmer and Bremner 1976). Delwiche ( in press) measured subambient

N̂ O leve ls in gas samples taken a t 18 cm so il depth.

Gas chromatography lends i t s e l f well to ^ 0 measurements.

Isotope d isc r im ina tion studies have demonstrated tha t mass spectrom­

e try may not be accurate fo r ^ 0 (Blackmer and Bremner 1977a), especi­

a l l y a t ambient concentration, approximately 330 ppb. Although the

thermal conduc t iv ity detector has been used in the past (LaHue,

Pate, and Lodge 1970), the e lectron capture detector w ith a Ni f o i l

(Wentworth and Freeman 1973) a t elevated temperatures (Schmeltekopf

et a l . 1977) can measure ambient N̂ O concentrations and recently the

u ltrason ic detector has demonstrated an exce llen t c a p a b i l i ty fo r

ambient NgO detection (Blackmer and Bremner 1977b). The ^ 0 sensi-63

t i v i t y o f the e lectron capture detector w ith a Ni f o i l increases

with temperature up to 350°C, which is i t s temperature l im i t w ith the

equipment ava ila b le . T r it ium f o i l can also be used in the electron

capture de tec to r, but i t vaporizes above 200°C and the detector must

be operated below th is temperature, decreasing i t s s e n s i t iv i t y .

In te r la b standardization has shown th a t the various gas chromato­

graphic set-ups gave consistent re su lts (Rasmussen and P ie ro t t i 1978).

37

Materia ls and Methods

The reaction chambers were 2.5 l i t e r glass reagent b o tt le s ,

12 cm in diameter, f i t t e d w ith a rubber septum in the 34 mm neck a t

the top fo r sample w ithdrawal. One chamber was l e f t empty to monitor

leakage from the vessels. A second chamber contained 200 ml o f d is ­

t i l l e d water to te s t the absorbing capacity o f water alone. Other

vessels contained 200 grams o f Gila sandy loam so il moistened with

d i f fe re n t amounts o f d i s t i l l e d water. The sp e c if ic treatments are

l is te d in Table 5. A fte r several days a t th is cond it ion open to the

a i r , the vessels were sealed and approximately 30 ppm N̂ O was in jected

in to the a i r above the s o i l .

In experiment 1, the vessels were sealed several days a f te r

wett ing . This permitted a small amount of the water to evaporate. In

experiment 2, the so i l was allowed to stand fo r two weeks in a sealed

vessel a f te r the water was added. They were then opened and allowed

to exchange w ith the a i r before the NgO was added.

Nitrous oxide leve ls were measured p e r io d ic a l ly by gas

chromatography. Two ml samples were withdrawn from the vessels w ith

a 2 ml gas syringe and in jected in to a Mikro-Tek gas chromatograph

equipped w ith a Hewlett-Packard 7650A electrometer and a Tracor

e lectron capture detector w ith a t r i t iu m f o i l . The electrometer was

capable o f providing 5, 15, 50, and 150 microsecond pulse in te rva ls

to the de tecto r. Five microseconds was used because i t was found

most sens it ive to N2 O. New syringes were used when the old ones

began to wear and were no longer gas t i g h t . The a i r components were

38

Table 5. Experimental Treatments of G ila Sandy Loam Soil and Other Reaction Chambers in a Study o f Nitrous Oxide Absorption

Soil Water % HgO % HoOExperiment (Grams) (ML) (w/w) ( v/v;

— 200 100 100

200 — — — — — — — — —

200 20 10 15

200 40 20 30

200 14 7 10

200 27 14 20

200 40 20 30

200 54 27 40

39

separated from N̂ O in a 3.15 meter by 3 mm s ta in less steel column

packed w ith 5.53 grams o f 100-120 mesh Porapak Q, g iv ing a packing

density o f 1.76 gr/cm. A 10 cm precolumn was packed w ith Mallcosorb

to remove CO2 because high CO2 concentrations in te r fe re w ith ^ 0

peaks.

Column oven temperature was 35°C and detector temperature was

maintained a t 170°C. Although the temperature l im i t o f the t r i t iu m

f o i l is 200°CS th is detector could not be heated above 170°C because

then the heat switch turned o f f and on and caused temperature v a r ia ­

t io n and corresponding f lu c tu a t io n s in the baseline. Column c a r r ie r

flow was 40 ml/min and scavenger gas flow in to the detector was

250 ml/min. These were found optimal fo r ^ 0 detection on th is in s t ru ­

ment by measuring the detector response to 50 ppm rLO over a wide

range o f operational cond itions. Column flow and oven temperatures

were those th a t provided the most e f f ic ie n t separation o f ^ 0 from

a i r . Scavenger flow was varied from 20 to 300 ml/min to f in d the

maximum detector response to N^O. The highest temperature th a t the

detector could maintain provided the maximum s e n s i t iv i t y and a steady

baseline. C arr ie r gas was e le c tron ic grade u lt ra -h ig h p u r i ty n i t r o ­

gen. The high grade was necessary because the COg and HgO contam­

inants in other grades appear as noise on the chromatogram.

The response of the e lectron capture detector to ^ 0 was not

constant. The detector f luc tu a te s due to i t s extreme s e n s i t iv i t y to

gas flow rates (espec ia lly scavenger f lo w ) , c a r r ie r gas p u r i ty ,

temperature, and humidity. Scavenger f low was shut o f f a f te r each

40

set o f samples was run in order to conserve gas. I t had to be read­

justed to the proper flow ra te before each set o f determinations.

The bubble flow meter could not contro l the scavenger f low to

exactly 250 ml/min. This was probably the major source o f f lu c tu a t io n

in the detector response to N^O. A standard curve had to be developed

w ith each set o f samples run. This was done by measuring the response

to 10, 15, 20, 30, and 50 ppm ^ 0 . F i f t y ppm c e r t i f ie d standard N̂ O

in Ng was purchased from Scott Specia lty Gases. D ilu t io n s o f th is

gas were made by drawing the proper proportions of ^ 0 and a i r in to

the syringe and in se rt in g the sample onto the column. The c a l ib ra t io n

curves were l in e a r , and concentrations o f the experimental samples

were determined from the graph o f the standard curve.

Results and Discussion

Figure 6 shows the re su lts o f experiment 1 by p lo t t in g the

n itrous oxide concentration in the atmosphere o f the reaction chamber

versus time. Raw data can be found in Table A-4 in Appendix A.

F luctuations in N̂ O concentrations fo r the Gila s o i l a t 15% (v /v)

and saturated water contents are evident in the f i r s t 200 hours. When

previously dry s o i ls are wetted, there is a burst in m icrobia l a c t iv ­

i t y . Growth of d e n i t r i f y in g bacteria was apparently stimulated and

appeared as an increase in N̂ O concentration.

A fte r 200 hours, the saturated so i l showed a remarkable

capacity to absorb N^O. The ^ 0 concentration decreased from 60 to2

10 ppm at a ra te o f approximately 2 ppm/day or 14 ppm/day-m . Con­

s idering th a t the i n i t i a l concentration was 45 ppm, extrapo la ting th is

41

QCLU

>-

N ITROUS 0X4 D̂ E PPM

Figure 6. Experiment 1 - - Changes in Nitrous Oxide w ith Time

100

200

300

400

500

600

700

900

TIM

E H

OU

RS

42

2ra te to ambient concentration gives 90 ppb/day-m , which is almost one-

quarter o f the ambient concentration. A fte r 600 hours, the s o i l ' s

ra te o f ^ 0 uptake decreased, which may be due to depletion of energy

sources or e lectron donors by the microorganisms.

A f te r 250 hours the so i l a t 15% (v /v ) water content also

absorbed N^O. The ^ 0 concentration decreased from 47 to 29 ppm at a2

ra te o f approximately 1.4 ppm/day or 10 ppm/day-m . Taking in to

account the o r ig in a l N̂ O concentration, the ra te o f uptake a t ambient2

concentration is extrapolated to 70 ppb/day-m . A fte r 550 hours, the

ra te leveled o f f and l i t t l e change in the h^O level was evident.

The N̂ O concentration did not change s ig n i f ic a n t ly in the a i r

above dry s o i l , d i s t i l l e d water, and in the empty con tro l chamber.

The s o lu b i l i t y o f N̂ O in water was smaller than could be measured.

Dry so i l had l i t t l e m icrobia l a c t i v i t y re la ted to uptake or relase o f

N2 O, and any physical in te rac t io ns o f ^ 0 and so il were not measurable.

Leakage from the chambers was below the l im i t o f de tection .

Figure 7 shows the re su lts of experiment 2 in which the so il

was allowed to stand fo r several weeks before N̂ O was in jected in to

the chambers. Raw data can be found in Table A-5 o f Appendix A.

F luctuations in N̂ O did not occur. The N̂ O decreased immediately

and s te a d i ly in the chambers containing so i l a t 30% and 40% (v /v)2

water content a t a ra te o f approximately 0.8 ppm/day or 5.7 ppm/day-m ,

from 36 to under 10 ppm. The N̂ O above the so il a t 10% and 20% (v /v )

water content f luc tua ted s l ig h t ly in the f i r s t 300 hours then

decreased s l ig h t ly , as did the con tro l chamber. The decrease may have

43

LU

LUj

CM

NITROUS OXIDE PPM

Figure 7. Experiment 2 - - Changes in Nitrous Oxide w ith Time

HO

UR

S

44

been due to leakage. A l l decreases ceased a f te r 750 hours and N̂ O

concentrations s ta b i l iz e d .

Wet s o i ls reduced atmospheric N^O. The so i l a t 40% (v /v )

water content had a th in layer o f water on the surface and only a

small amount o f a i r present as trapped a i r bubbles. In anaerobic

s o i ls , such as the saturated and 40% (v /v ) water content, microorga­

nisms reduce the N̂ O to using the N̂ O in place o f 0^ as an electron

acceptor (Bremner in press). In s o i ls w ith anaerobic s i te s , such as

the so i l at 30% (v /v ) water content, ^ 0 reduction also occurs. The

aeration o f the so i l is important in determining the extent o f N̂ O

uptake by the s o i l . Dry so i l and s o i ls w ith small amounts o f water

have aerobic conditions and l i t t l e capacity to reduce N̂ O concentra­

t io n s .

I n i t i a l N̂ O concentrations were not equal in a l l chambers

because i t was not possible to in je c t exactly the same amount o f N̂ O

in to each chamber. The chambers did not have the same amount o f a i r

space in them, and the contro l chambers had more a i r space since

there was no l iq u id or so lid present.

Oxygen concentrations were not measured, but an O2 peak was

eluted p r io r to the ^ 0 peak. A s l ig h t decrease in oxygen was noticed

on saturated and 15% (v /v ) water content from experiment 1 and 30% and

40% (v /v ) water content from experiment 2. Probably 0^ was being con­

sumed by microorganisms. Oxygen was s t i l l present in the atmosphere,

but NpO reduction occurs only a t anaerobic s i te s .

45

Blackmer and Bremner (1976) showed tha t high n i t r a te concen­

t ra t io n s in s o i ls in h ib i t reduction o f N̂ O to Ng. The so i l used in

th is study was not treated w ith n i t ra te s and had a low n i t r a te le v e l.

Natural, non-agricu ltu ra l s o i ls and p a r t ic u la r ly desert s o i ls have

re la t iv e ly low n i t r a te leve ls .

Nitrous oxide was released by s o i ls a t saturated and 15% (v /v )

water contents in experiment 1, but w ith time the NgO decreased below

the o r ig in a l concentration. So ils in experiment 2 released l i t t l e or

no NgO. Allowing newly wetted so il to stand fo r several weeks before

exposing them to a i r and then in je c t in g N̂ O elim inates the release

o f N2 O during the experiment and the use o f much o f the oxygen in the

chamber by the microorganisms.

The amount o f N̂ O in jec ted in to the so i l atmosphere (30 ppm)

was about 100 times ambient concentrations. The saturated so il in9

experiment 1 reduced NgO by 50 ppm at a ra te o f up to 14 ppm/day-m .

I f the concentration o f NgO in the atmosphere is high enough, a

square meter o f so i l can reduce atmospheric N2 O concentrations up to

40 times the ambient concentration in a day.

I t is becoming more evident th a t s o i ls have the capacity to

act as both a source and sink fo r NgO. The moisture status of the

so il con tr ibu tes to determining the extent o f release or uptake of

N2 O. Anaerobic s ite s are necessary and high water contents are

optimum fo r anaerobic conditions.

Conclusion

Soils w ith anaerobic s ite s are capable o f reducing atmo­

spheric NgO le v e ls ; saturated s o i ls are capable of reducing N^O.

Dry s o i ls showed no con tr ibu t ion in the ^ 0 cyc l ing , but newly wetted

s o i ls are capable o f re leasing N^O. With time, some s o i ls tha t pre­

v ious ly released f^O are capable o f absorbing ^ 0 . I t is l i k e ly

tha t many fa c to rs , such as water s ta tus, organic matter, and n i t ra te

leve ls determine i f a so il w i l l release or take up ^ 0 . So ils e x is t

in a wide range of cond it ions , and the conditions determine what ro le

the s o i l plays in N^O's geochemical cyc l ing .

APPENDIX A

RAW DATA TABLES

47

,48

Table A -l. Specific Retention Volume of Various Hydrocarbons atDi fferent Column.Temperatures

Compound T°C log Vg Compound T°C log '

methane a l l .072 acetylene 28 1.0536 .89

ethane 28 .28 43 .7537 .23 53 .6145 .19 64 .5053 .15 75 .38

propane ' 28 .82 iso-octane 143 1 . 1 237 .65 156 .9345 .57 165 .7653 .47 175 .5364 .37 185 .3774 .27

cyclohexane 111 1.08butane 46 1.04 125 . 8 6

62 .79 135 .6775 .70 143 .5986 .53 " 156 .3795 .45

111 .37 iso-butylene 111 1.03125 .81

hexane 125 1.15 135 .62135 .93 143 .53143 .76 156 .32156 .60165 .45 pentene 125 1.19

135 1.08heptane 155 1.05 143 . 8 6

165 .83 156 .59175 .69 165 .45185 .56

1.11194 .51 toluene 175185 .62

octane 170 1.09 194 .49176 .97186 .81 benzene 185 1.23

194 1.09ethylene 28 .47

36 .4043 .31

. 53 .2664 .17

49

Table A-2. Specific Retention Volume o f Hexane on Various Soils a tD iffe ren t Column Temperatures

Soils. T°C log Vg

Kalkaska 40 1.2745 1.1550 1.07

„ 75 .55. 90 .37

Fanno. 105 2.16120 1.91135 . 1.57150 1.33

Gila Fine Sandy Loam 99 1.96110 1.57125 1.26139 1.01

Gila Sandy Loam , 7 7 1.758 8 1.55

102 1.321 1 2 . 1.08 125 ' .81

Mohall 135 1.64139 1.55151 1.36163 1.23173 1.05

50

Table A-3. Specific Retention Volume o f JP-4 Components a tD iffe ren t Column Temperature

Peak T0C log Vg Peak T°C log Vg

A 40 .62 D 69 1.1746 .53 81 1.0450 ,47 91 .9352 .46 1 0 0 .8060 .37 109 .6969 .34 1 2 0 .5681 .26 121 .4991. .19 . 127 .46

1 0 0 . 1 1 145 .17

B 46 1.06 E 91 1.1850 . .91 1 0 0 1.0352 .89 109 .8960 .72 1 2 0 .72

' 69 . 6 6 121 . 6 881 .49 127 .6291 .41 145 .37

1 0 0 .34109 .27 : F 109 1 . 2 0

1 2 0 1 . 0 1C 50 1 . 2 0 121 .94

52 1.19 127 .8560 .99 - 145 .6269 .8981 .6991 .58

1 0 0 .49109 .41121 .29

51

Table A-4. Experiment 1 - - Nitrous Oxide Concentrations in ReactionChambers

NgO Concentration in Chambers (ppm)~ " Soil a t Soil a t

15% v/v SaturatedTime Empty Water Dry Water Water(hours) Control . Only So il Content Content

24 1.8 27 17 42 45

45 18 28 18 58 44

117 16 26 18 36 39

184 17 26 17 44 56

254 18 26 18 47 46

398 . 17 25 17 38 36

544 17 24 17 29 21

621 17 26 17 29 19

880 17 26 16 31 14

52

Table A-5. Experiment 2 - - Nitrous Oxide Concentrations in ReactionChambers

NgO Concentration in Reaction Chambers

, Soil a t Water ContentT ime Empty . : . .(hours) Control 10% v/v 20% v/v 30% v/v 40% v/v

24 22 31 34 35 36

72 23 33 39 34 35

140 23 31 37 26 30

188 22 32 39 25 27

254 23 33 37 23 14

398 2 2 31 37 . 19 19

466 21 30 35 16 16

657 19 27 31 11 11

758 18 26 32 10 8

971 19 26 34 11 9

• APPENDIX B

CHROMATOGRAMS AND MASS SPECTRA FIGURES

53

1 cc JP-4 Vapor

In je c t io n

Column Temp. 90 C

Column Flow Rate 60 ml /min

Chart Speed 13 mm /min

Figure B - l . Chromatogram of JP-4 Vapor on Gila Sandy Loam Soil Column

55

SPECTRUM 7

SPECTRUM 37

n _

^-SPEC TR UM 11 6

•-S P E C TR U M

■SPECTRUM 196

RESPONSE

Figure B-2. Reconstructed Chromatogram of JP-4 Vapor from MassSpectrometer-Gas Chromatograph

Perc

ent

of H

ighe

st

Peak

44

56

_|Uuiylll50

Figure B-

Propane

Atomic Mass Units 100

3. Mass Spectrum 7

Perc

ent

of H

iqhe

st

Peak

43

57

2, Methyl Propane

58

10050 Atomic Mass Units

Figure B-4. Mass Spectrum 23

Perc

ent

of H

ighe

st

Peak

58

Butane

58

Atomic Mass Units 100

Figure B-5. Mass Spectrum 37

Perc

ent

of H

ighe

st

Peak

43

59

2, Methyl Butane

58

llLm.72

h in L ■Hi I lull | illGO Atomic Mass Units 10D

Figure B-6. Mass Spectrum 84

43

Pentane

72

57

illljL30

ll,ll L41 till U,. l l l i . ll.ilr 1 1 Iv » r rAtomic Mass Units 100

Figure B-7. Mass Spectrum 114

Perc

ent

of H

ighe

st

Peak

Hexene

84

100Atomic Mass Units

Figure B-8. Mass Spectrum 145

Perc

ent

of M

iohe

st

Peak

41

62

Methyl Cyclohexane

83

55 70

lUlijl

98

I I I L k U i

so Atomic Mass Units 10 D

Figure B-9. Mass Spectrum 196

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