Peroxynitrite: A Re-examination of the Chemical Properties of Non-thermal Discharges Burning in Air...

ORI GIN AL PA PER

Peroxynitrite: A Re-examination of the ChemicalProperties of Non-thermal Discharges Burning in AirOver Aqueous Solutions

Jean-Louis Brisset • Eugen Hnatiuc

Received: 21 December 2011 / Accepted: 27 April 2012 / Published online: 20 May 2012� Springer Science+Business Media, LLC 2012

Abstract The main compounds of non-thermal plasmas generated by a discharge in

humid air at atmospheric pressure are re-examined to explain the twin chemical properties

of discharges over aqueous waste solutions, i.e. the acid and oxidizing effects. The acid

effects are attributed to transient nitrous and peroxynitrous acids and to stable nitric acid.

The matching oxidizing power of the discharge species onto solutes is due to water soluble

H2O2 provided by the dimer formation of �OH and also to peroxynitrous acid ONOOH and

its salt which are involved in the oxidation process of nitrous to nitric acid.

Keywords Cold plasma � Reactive nitrogen species � Acid effects �Transient nitrite � Peroxynitrite

Introduction

The question of the acid effects induced by discharges burning in air over aqueous solu-

tions at atmospheric pressure remains a key problem, since it implies the still unelucidated

water plasma interactions although the effects in a target solution are easily evidenced and

measured. These effects result from an increase in the acidity level of the medium exposed

to the discharge. Such a feature is now largely admitted but not well understood yet. The so

called ‘‘acid effects’’ or ‘‘acid plasma’’ are essential in most environmental processes

which involve oxidation phenomena in the degradation of organic wastes, the bleaching of

dye solutions and the control the matching kinetics thus require a new examination.

The oxidizing degradation of organic compounds is usually governed by thermody-

namic laws, and in particular Nernst’s: in other words an electrochemical reaction such as

Oxidantþ qHþ þ ne�\¼[ Reducer

J.-L. Brisset (&)Faculty of Sciences, University of Rouen, 76821 Mont Saint-Aiganan, Francee-mail: [email protected]

E. HnatiucUniversitate Apollonia din Iasi, Iasi, Romania

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Plasma Chem Plasma Process (2012) 32:655–674DOI 10.1007/s11090-012-9384-x

is controlled by the proton activity aH? or the pH function (pH = -log aH? & -log

CH?) which may be approximated by the co-logarithm of the proton concentration in

dilute solutions. Consequently, the overall reaction resulting from the interacting two

Oxidizer/Reducer systems {1} and {2}, i.e.,

n2Ox1 þ n1Red2 þ ðn2q1 � n1q2Þ Hþ\¼[ n2Red1 þ n1Ox2

involves the proton concentration. Then, the above reaction which is thermodynamically

determined by the difference in the Gibbs free energy of the systems and the relevant DG

value

DG ¼ n2FE2 � n1FE1

is also affected by the local acidity, i.e., by the rate control term (n2q1 - n1q2) CH?.

We have thus to examine the question of the proton generation in an aqueous solution

under discharge conditions, and we shall focus on three types of non-thermal plasmas, i.e.,

corona, dielectric barrier discharge DBD or quenched gliding arc discharges for illustration

purposes. It must firstly be pointed out that a gliding arc discharge (or ‘‘glidarc’’) is not a

thermal plasma despite it is generated by an arc. It is actually a quenched plasma at

atmospheric pressure and nearly ambient temperature and thus belongs to this family of

discharges in spite of its particular characteristics.

The glidarc proposed by Czernichowski et al. [1] some thirty years ago works as

follows: two diverging electrodes are connected to a suitable HV source (by few kV) so

that an arc forms at the narrowest gap (here occurs a thermal plasma). The feet of the arc

are gently blown along the electrodes to their tips by a gas flow of water saturated air

directed along the axis of the reactor. The arc length increases as its temperature falls until

it breaks when it is short-circuited by a new arc and the resulting plasma plume (or

‘‘cloud’’) is a quenched non-thermal plasma with the components of a thermal plasma and

the properties of a cold plasma. Temperature measurements of liquids exposed to the

discharge confirmed the very limited thermal effect of this process which thus enables us to

perform liquid treatments.

From the electrical point of view all the concerned discharges are operated in a range of

the current intensity vs. applied voltage curve as illustrated in [2] between the corona

discharges and the arcs. It is clear that an arc is a thermal plasma, with the relevant

properties.

The particular feature of the glidarc (Fig. 1) results from the working conditions and the

design of the reactor. For example, using a HV transformer, e.g., an Aupem-Sefli 9000 HV

Transformer delivering 9 kV- 0.1A or 600 V- 160 mA in open and working conditions

respectively, induces very moderate temperature changes of a liquid pool disposed in front

of the electrodes and thus in contact with the plasma plume.

The temperature of aqueous targets exposed to the discharge at various distances was

measured (Table 1 and Fig. 2) [3, 4] and confirms the quenched character of the plume.

The thermal effect cannot reasonably be held as the cause of lethal effects for bacteria,

provided the distance between the electrode tips and the liquid surface is longer than

150 mm. The temperature of the liquid target rapidly rises and tends to a plateau for

t* C 15 min [3]. A typical plot is showed in Fig. 2.

Such working properties allow using the glidarc plasma device as a tool for the treat-

ment of liquids in the same way as corona or DBD devices, e.g., for pollutant abatement of

harmful organic solutes in wastewaters in batch or circulating conditions, or inactivation of

bacteria in their various development states [4]. The liquid target is disposed under the

656 Plasma Chem Plasma Process (2012) 32:655–674

123

discharge at the distance d from the electrodes tips and perpendicularly to the axis of the

reactor as sketched in Fig. 1. The thermal effect is limited as discussed above, which is

essential for microbiology studies, so that a temperature rise by few tens of degrees is

expected without using a cooling jacket around the jar. The cooling system is used for

security reasons, to avoid reaching flashpoints in the treatment of volatile industrial waste

solvents. Air is directly provided by a compressor and passes through a flowmeter and a

bubbling flask filled with water to get water saturated air before entering the reactor.

We have now to examine the main species formed in the discharges generated in humid

air and underline their major chemical properties, with the aim of completing previous

studies [4–7].

Parent species (humid air)O2, N2, H2O

Main Primary species:H°; °OH; O2*; H2O*; O; N; IonsSecondary species: O2+, O+; N2+; N+;OH-; NO2

-; NO3-; ONO2

-; H, OH, H2O2 ;(HO2; O3); NO; NO2 ; ONO2HMain primary and secondaryimpinging species: NO2

-; NO3-; ONOO-

;H+; H2O2 ;(HO2); NO; ONO2H

Gliding DischargeHigh voltage source

Diverging electrodes

Gliding arc:Thermal plasma

Quenched plasma

Water surface

Waste solute

Fig. 1 Sketch of a gliding arc reactor with the assumed distribution of the main gaseous species

Table 1 Thermal effect of thedischarge on aqueous solutions(24 mL) [3]

Gas flow rate 500 Lh-1

Distance D electrode tip/water (mm) 14 220

Exposure time t* (min) 5 30

DT = (T - T0) (�C) 30 9

Paraffin wax test (Fusion Temperature: 52 �C) [52 \52

0 10 20 30 40 50 60 700

5

10

15

20

25

t*, min

T, °

C

Fig. 2 Typical plot ofTemperature increase of a(24 mL) aqueous target with theexposure time t* (min). After asteep increase for shorttreatments t* \ 5 min, thetemperature tends to a plateau.Gas flow:550 Lh-1; distanceelectrode-liquid: 220 mm [3]

Plasma Chem Plasma Process (2012) 32:655–674 657

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Formal Distribution of the Main Active Species

The distributions of the active species are similar for all the discharges at atmospheric

pressure, especially for corona and gliding discharges (Figs. 1 and 3). We shall focus on

the last ones because of the amount of energy delivered to the arc in the case of glidarc is

higher than for corona discharges, so that the resulting quantity of formed activated species

is increased and the chemical effects are much more easy to be evidenced and quantified.

For the sake of simplicity, we split the plasma reactor into several zones, with special

components, e.g., the Parent molecules at the gas inlet, the Primary species around the

ionization zone where the major part of the energy transfer takes place, the Secondaryspecies in the plasma cloud in contact with the target.

Energy consideration shows that the energy amount displayed in cold plasmas remains

in the approximate range 1–3 eV (100–300 kJ mol-1), i.e., in a largely lower range than

thermal plasmas, so that direct ionization or/and direct homolytic bond breakings (which

require around 900 kJ mol-1) by electron impact are more unusual processes than for

arcs (Table 2). In the plasma plume of a glidarc, which is a quenched plasma as men-

tioned, the occurrence of ions and of more energetic moieties than in coronas is thus

being expected.

Also we shall focus on discharges in natural or humid air, because of the large use of

this gas mixture, due to its low price. Incidentally, the gas surrounding discharges burning

in air over an aqueous film readily changes to water saturated air by evaporation of the

target, so that the properties of the ambient medium are modified. Lot of papers consider

the influence of water on the gas composition around the discharge, and their authors agree

to account for a positive effect especially in case of pollutant abatement or microbial

inactivation.

Ambient gas O2;N2;H2OHV+ HV-

Corona (Point-plane)

Primary speciesH; OH; O2*; O; N; ions, e-

Cations Anions; e-

Earthed grid

Secondary neutral speciesOH, H2O2, NO; ONO2H

Target H+, NO2

-,NO3-

Fig. 3 Sketch of the distribution of species in a d.c. Corona discharge fitted with an ion trapping grid


123

The Parent Species in Case of a Discharge in Humid Air

The parent molecules present in humid air are mainly O2, N2 and H2O molecules which

constitute a gaseous mixture sensibly different from dry air, and much more different from

pure N2 or pure O2 gases. Most of these species are initially in their natural ground state.

The Primary Species

The energy transfer from the electric field lines to the ambient gas induces several affects,

according to the quantity of transferred energy (and the power delivered by the electric

source), in particular excitation and ionization for high energy transfers.

In the arc (or at the immediate neighbourhood of the HV electrode of a corona dis-

charge), the energy transfer to the gas is maximum and activation of the gas molecules

results: O2 and N2 molecules are raised to excited states, as are the water molecules for

moderate energy transfers. The species thus formed in the thermal zone are excited

Oxygen, Nitrogen, water molecules and radicals such as �H, �OH and �O resulting of

homolytic breaking of the H–OH and O = O bonds respectively. Dissociation of Nitrogen

molecules is more energetic than for Oxygen molecules and requires 9.8 eV (945 kJ

mol-1), so that dissociation and excitation will preferentially concern Oxygen in low

energy discharges. The formation of hydroxyl radicals which is observed and quantified by

emission spectroscopy in case of glidarc [8, 9] is attributed to electron impact at activated

water molecules:

e�þ H2O X1A1

� �! e�þ H� þ �OH

Table 2 An energy overview of the most numerous species encounted in cold or quenched discharges(1 eV mol-1 = 96.5 kJ mol-1)

Species Excitation energy(kJ mol-1)

Dissociationenthalpy (kJ mol-1)

Ionization(kJ mol-1)

Lifetimegas (s)

O2 0 (3Rg-)

94.3(1Dg)156.9(3Rg

-)

500 1,167 –45 min (gas)7–12

N2 0598 (A3Ru

?)695 (B3Pg)1,080 (C3Pu)

945 1,515 –21.7 9 10-6

3.2 9 10-8

H2O 0 (X1A1)714 (A1B1)859 (3A2)878 (1A2)

494 1,216 –

O – 1,314

N – 1,402

OH 0 (X2P) 463 1,161 Few hundreds ns

H 984 (22S�) 1,312 1

NO 0 (X2P)530 (A2R?)

305

Data from ‘‘Book of Data’’ R. Harrison, Ed.; Lowe & Brydone Ltd (1975), Thetford, Norfolk


123

which accounts for the reaction file:

e�þ H2O X1A1

� �! e�þ H2O 3A2

� �! e�þ H�ð2S)þ �OH

! e�þ H2O A1B1

� �! e�þ H�ð2S)þ �OH X2P

� �

! e�þ H2O A3B1


� �

! e�þ H2O A3B2


� �

! e�þ H2O B1B1

� �! e�þ O�ð1D)þ H2 X1Rþ

� �

Other reactions also occur and involve ionic species, such as N2? in the glidarc [9] but

its concentration remains low. Activated species involving Oxygen or Nitrogen are usually

referred to as Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS)

respectively.

The Secondary Species: Reactive Oxygen Species (ROS)

The primary species react with other primary species or with parent species and give rise to

new species called secondary species. Some of them are of special interest.

The Hydroxyl Radical �OH

The hydroxyl radical �OH is probably the most important species spectroscopically

identified [8, 9] in the discharges because of its oxidizing properties. �OH is mainly formed

by electron impact on excited water molecules as mentioned, but other sources probably

exist, apart photon impact on hydrogen peroxide, e.g.,

H2O2 þ hm! 2 �OH

e�þ H2O! H� þ �OH ðenergy threshold : 5:7 eV or 550 kJmol�1ÞHO�2 þ O3 ! �OHþ 2O2

HO�2 þ �NO! �OHþ NO2

Several other reactions may be involved in the plasma processess and form �OH rad-

icals, but they cannot be considered as the main sources of reactive �OH, although they are

not discarded from the overall mechanism, e.g.,

HO�2 þ H2O2 ! �OHþ O2 þ H2O

HO�2 þ H2O! H2O2 þ �OH

NO2 þ H� ! �NOþ �OH

The lifetime of the �OH radicals (i.e., few hundreds of ns) formed in the arc zone of a

gliding discharge is too short to allow the species to move in the gas without being

disactivated and to reach the liquid surface. In quasi-standard conditions (gas flow

Q = 600 Lh-1; nozzle area: 1 mm2), the distance covered by �OH in an assumed cylinder

of 1 mm2 section is 0.017 cm for 1 ls. Thus the formation of derivatives must be con-

sidered in the gas phase and tentatively attributed to the formation of clusters or dimers for

example.

An assumption which requires further experimental results may be tentatively proposed,

on the base of studies of atmospheric chemistry and concerns the formation of clusters in

the gas phase [10].

�OHþ n H2O! �OH H2Oð Þnwith n ¼ 1�5


123

These hydroxyl radical-water molecules adducts (or complexes), i.e., �OH(H2O)n,

formed in the gas phase should be highly soluble in water and present similar oxidizing

properties as the starting �OH, with slightly stabilized oxidation potentials which would yet

remain largely higher than that of most organic systems. This feature would explain the

degrading power of the plasma treatments and in particular the post-discharges effects

which will be discussed below.

Hydrogen Peroxide H2O2

Two hydroxyl radicals react together and yield the dimer hydrogen peroxide H2O2

HO� þ �OH! HO-OH

with a kinetic constant around k = 5.5 9 109 Lmol-1s-1, i.e., a value close to those

reported in acidic irradiated water [11].

The formation of the dimer HO–OH, may take place in the gas phase. Hydrogen

peroxide is very soluble in water: it may easily dissolve in the liquid and then react with

solutes.

The occurrence H2O2 in the plasma treated aqueous target is evidenced by the formation

of metal complexes (e.g., with TiIV or VV) in the solution. However, such tests remain

qualitative, because of post discharge phenomena which may favour or lower the con-

centration of H2O2.

Other side reactions may favour the formation of hydrogen peroxide, e.g.,

HO�2 þ HO�2 ! H2O2 þ O2 ð2k ¼ 3:7� 105dm3mol�1s�1Þ ½12�

(k = {2.2 9 10-13 exp(600/T) ? 1.9 9 10-33 [N2]exp (980/T)} 9 [1 ? 1.4 9 10-21

exp (2,200/T)[H2O]) in the temperature range 200 \ T, K \ 500 [13]

or

O2 þ H� ! HO�2ðk ¼ 21� 1010dm3mol�1s�1Þ 15½ �2HO�2 þ 2O3 ! H2O2 þ 4O2ðk\104dm3mol�1s�1Þ 14½ �

Peroxyl Radical �O2H

The peroxyl radical form by the fixation of H� radicals on O2 according to known reactions

in pulse radiolysis studies, e.g.,:

H� þ O2 þM! HO�2 þM

or

�OHþ H2O2 ! HO�2 þ H2O ðk ¼ 12� 107M�1s�1at 0:4\pH\3Þ

�OH also reacts with ozone and forms HO2�:

�OHþ O3 ! HO�2 þ O2 k ¼ 1:1� 108dm3mol�1s�1� �

14½ �

which disproportionates in water:

HO�2 þ HO�2 ! H2O2 þ O2 ð2k ¼ 3:7� 106dm3mol�1s�1Þ ½14�


123

HO�2 þ NO2 ! HO2NO2 ðk ¼ 107 � 1:8� 109dm3mol�1s�1Þ ½16�

HO�2 þ NO� ! ONOOH ðk ¼ 32� 109dm3mol�1s�1Þ ½16�

The Secondary Species: Reactive Nitrogen Species (RNS)

The most important RNS in our case are nitric oxide NO, nitrous acid HONO (and the

matching base nitrite), peroxynitrous acid ONOOH [and its salt peroxynitrite, also called

oxoperoxonitrate (-1) according to IUPAC nomenclature] and its isomeric nitric acid. The

present study is limited to these few N-containing species as a first approach for the sake of

simplicity because they appear to be essential to a better understanding of the environ-

mental action of the electric discharges.

Nitric Oxide NO and Nitrogen Dioxide NO2

N2 combines with O2 and yields nitric oxide NO� which is identified in the arc zone and

quantified by emission spectroscopy [8, 9]. The formation of NO� is largely endothermic

(DH�298 = 90.3 kJmol-1) as is the dissociation (DH� # 630 kJmol-1) [17] and takes place

in combustion processes [20]. NO� was identified in the arc zone of a gliding discharge and

also found in the plasma plume. The widely accepted Zeldovich model for its formation is

a chain reaction which involves the oxidation of N2 by O atoms according to a more

complex mechanism than the mere balance N2 ? O2 ? 2NO�.

N2 þ O� ! NO� þ N�

N� þ O2 ! NO� þ O�

N� þ O� ! NO�

NO� has limited stability (lifetime of a few seconds); it is soluble in water (74 mL/L at

STP), toxic and able to diffuse through membranes, which explains its lethal action on

bacteria including DNA damage and its biological action. For example NO� easily binds

with metalloproteins, and in particular its affinity with Hemoglobin is 1,500 times that of

carbon monoxide CO [17].

It seems pertinent to report some basic information on NO� and its oxidation product,

Nitrogen dioxide, which are carefully examined by Biologists. NO� is a reacting species

well known for its occurrence in many physiological and pathological processes and in

atmospheric chemistry. It is widely accepted that Nitric oxide is unstable in air and reacts

with the surrounding O2 and yields NO2 by a complex mechanism which involves several

nitrogen oxides.

At low temperature, NO� reacts with N atoms according to an exoergic reac-

tion 3.25 eV [18]:

NO� þ N� ! N2 þ O�

The reaction of NO� with �OH develops according to a termolecular process:

NO� þ �OH þMð Þ ! HONO þMð Þ

fk�ðT)[N2� ¼ 7:4� 10�31ðT=300Þ�2:4½N2� cm3molecule�1s�1g 21½ �


123

which was extensively studied in atmospheric chemistry since NO is concerned in the

cycle of ozone O3:

NO� þ O3 ! NO2 þ O2 þ hm

The disappearance reaction of NO�

NO� þ HO�2 ! �OHþ NO2

is characterized by an increasing rate constant with decreasing temperature [18]. Addi-

tionally NO� gives an adduct with hydroperoxyl radical, which is of major importance for

biological studies of bacterial stress and consequently for our purpose of decontamination

of organic wastes and bacterial inactivation [19]:

NO� þ HO2 ! ONOOH ðk ¼ 3:2� 109Lmole�1s�1Þ 16½ �

NO2 disappears by impact of energetic photons (k\ 430 nm) which break one N–O bond:

NO2 þ hm! O(3P)þ NO�

and leads to further ozone formation. However ozone reacts with NO2 and remains as

traces in solution.

NO2 þ O3 ! NO�3 þ O2

Also:

NO2 þ HO�2 ! O2NOOH ðk ¼ 107 � 18� 109L mole�1s�1Þ 16½ �O2NOOH! HO�2 þ NO2ðk ¼ 86� 10�3s�1Þ 16½ �O2NOOH! HNO2 þ O2 ðk ¼ 70� 10�4s�1Þ 16½ �O2NOOHþ HNO2 ! 2Hþ þ 2NO�3 k ¼ 12ð Þ 16½ �

Nitrous Acid and Nitrite

In aqueous solution, nitric oxide reacts with dissolved oxygen and yields nitrite ions

according to the overall reaction

4 NO� þ O2 þ 2 H2O! 4 NO�2 þ 4 Hþ 16½ �

which accounts for the proposed steps [16]:

NO� þ O2 ¼ ONOO

ONOOþ NO� ! ONOONO

ONOONO! 2 NO2

NO2 þ NO� ! N2O3

N2O3 þ H2O! 2 NO�2 þ 2Hþ

The transient character of nitrite ions is evidenced from treatments of water by both

corona (Fig. 4a,b) and gliding discharges (Fig. 5), since the relevant concentration first

increases then decreases with increasing exposure time [22, 23].

Additionally, slightly different results relevant to the nitrite and nitrate concentrations

are provided by experiments performed without pulsed discharges [23], with an ‘‘open’’ or

a ‘‘closed ‘‘ reactor at a fixed gas flowrate 900 Lh-1. With an ‘‘open’’ reactor, the nitrate


123

concentration rapidly reaches a plateau while it continuously increases with a ‘‘closed

reactor’’. The nitrite concentration presents a maximum for short exposure times t* for both

open and closed reactors, a feature which accounts for the occurrence of two opposite

overall reactions. Also, the shapes of the CNO2- vs. t* plots are affected by the gas flowrate:

the occurrence of a maximum is more clear for high flow rates (e.g., 900 Lh-1) than for

low flowrates (such as 500 Lh-1) with a maximumin the same time range. A tentative

explanation lies in the residence time of the gas in the arc which favours the formation of

ONO and ONOOH with respect of that of ONOH.

It is clear that aqueous solutions exposed to the discharge enrich in transient nitrite ions,

as the proton concentration increases. The NO2- concentration tends to a plateau for

increasing exposure times. This feature implies that disappearance of NO2- also takes

place, as the nitrate concentration increases. Such an evolution may be explained by the

0 50 100 150 200 2500

0.5

1

1.5

2

2.5

3

3.5C(NO2)90µA

C(NO2)50µA

C(NO2)15µA

Exposure time t* (min)

C(N

O2-

),m

gL

-1

a b

Fig. 4 a Effects of the current intensity on the Nitrite concentration in a dc negative corona in air (electrodegap 11 mm; point to target 20 mm); b Formation of Nitrate in a dc negative corona in air (electrode gap11 mm; point to target 20 mm; I = 90 lA) [22]

Fig. 5 Effects of the air flow rate on the formation of nitrite in a gliding discharge in humid air (emptysquares: 500 Lh-1; diamonds: 700 Lh-1; black triangles: 900 Lh-1) [23]


123

concomitant pH decrease and the lack of stability of nitrous acid in acid medium as

developed below.

The Nitrogen atom in Nitrous acid HNO2 [pKa = 3.3] and the matching base nitrite

NO2- has the oxidation number (?III). These compounds may be reduced to NO and

oxidized to stable NO3- depending on the local acidity. The scheme (Fig. 6) of the

variations of the formal potential with acidity (pH), namely the E’� vs. pH plots, were built

on the values of standard oxidation potentials of NO3-/HNO2; NO3

-/NO2-; NO2

-/NO and

NO3-/NO systems reported in Table 5, shows that nitrous acid is unstable in solution and

that stable nitrite ions can be present only for pH [ 6.

Peroxynitrous Acid ONOOH; Peroxynitrite ONOO-

Peroxynitrite, also called oxoperoxonitrate(-1) and its matching acid are among the

‘‘recently’’ discovered species since the first relevant reports on the species were published

by Halfpenny and Robinson [24] towards the mid-20th Century. The literature is poor in

relevant reports up to the Nineties [25]. Biologists and physicians resumed studying these

compounds and evidenced their occurrence in major neurodegenerative diseases, such as

Parkinson’s or Alzheimer’s diseases or even gut inflammation [17, 26–30]. They also

underlined their action in bacterial oxidizing stress processes, so that ONOO- is involved

in both necrotic and apoptotic cell death.

Peroxynitrite results from the mixing sodium nitrite (0.2 molL-1) with hydrogen per-

oxide (1 molL-1) in cold concentrated potassium hydroxide solutions (1.5 mol L-1); the

concentration of the product is determined spectrophotometrically at 302 nm [31].

H2O2 þ NO�2 ! ONOO� þ H2O

Other reactions occurring in radiolysis of water produce ONOOH or its salt, e.g.,

NO� þ O�2 ! ONOO� ðk ¼ 4:3� 109�6:7� 109Lmol�1s�1Þ ½31� 34�NO� þ HO2 ! ONOOH ðk ¼ 3:2� 109Lmol�1s�1Þ 16½ �NO2 þ�OH! ONOOH ðk ¼ 1:3� 109�1:2� 1010Lmol�1s�1Þ 16½ �

Fig. 6 Formal potential E’� vs pH plot showing the thermodynamic unstability of nitrous acid bydisproportionation at low pH. The graph is built with the values of standard potentials vs SHE: E� (NO3

-/NO) = 0.96 V; E�(NO3

-/NO2H) = 0.94 V and E�(NO2H/NO) = 1.00 V (see Table 4) and pKa(HNO2/NO2

-) = 3.3


123

Katsumura [16] also reports kinetic rate constants for the formation and the dissociation

of peroxynitrous acid

ONOOH$ Hþ þ ONO�2 ðkforward ¼ 1:6� 104s�1; kbackward ¼ 5� 1010s�1�

and the isomerization rate constant to nitric acid:

ONOOH! Hþ þ NO�3 k ¼ 1:1s�1� �

This set of reactions accounts for the formations of transient nitrous and peroxynitrous

acids which ultimately enrich the plasma treated solution with nitric acid.

The Puzzling Oxidation of Nitrite to Nitrate

The thermodynamic considerations above developed account for equilibria, but not for

kinetics between species and thus must be completed with geometric arguments to account

for a complex mechanism. It must be noticed first that the structure of NO is obviously

linear, as is that of nitronium ion [ONO?] but nitrite is bent (115�) and nitrate is trigonal.

The oxidation of nitrite to nitrate is thus not simple and requires guessing the occurrence of

an intermediate, such as peroxynitrous acid. In the peroxynitrous form, the oxidation

number of Nitrogen is that of its highest state, i.e., [V], just as in nitrate ions. Thus it may

be considered as an isomer of nitrate (or nitric acid), and more precisely a precursor, since

HNOOH reacts in the presence of water and releases nitric acid (H? ? NO3-):

ONOOHþ H2O! Hþ þ NO�3 þ H2O ðk ¼ 1:1 s�1Þ 16½ �

It thus becomes highly attractive to examine possible reactions files beween identified NO

and nitrate involving peroxynitrite. A general reaction scheme was recently reported [17]

and mentioned the occurrence of an activated intermediate [ONOO]. Figure 7 illustrates

the place of peroxynitrite as a reacting intermediate.

Chemical Properties of ROS and RNS

Both ROS and RNS present acid–base and oxidation–reduction properties, which explains

their collective reactivity and the environmental efficacy of the plasma treatments for

removing organic wastes and bacterial inactivation.

Fig. 7 Sketch of the interactions between selected ROS and RNS with emphasize on the situation ofONOOH as an intermediate. The relevant reactions are mentioned in the text with their kinetic constants inmost cases


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Acid Base Properties

The acid base properties limited to proton exchange of the most common ROS and RNS

are gathered in Table 3, as equilibria involving the proton donor acid AH and the matching

proton acceptor, i.e., the base A-:

AH ¼ A� þ Hþ

The associated equilibrium constants Ka (or pKa = -log Ka) are also reported. It may

be reminded that the usual acidity scale in water is the pH scale: pH = -log aH? &-logCH? in dilute aqueous solutions, where aH? and CH? respectively refer to the

activity and the concentration of protons. Also, it is easily showed that for pH \ pKa - 1,

the concentration of the acid form is by 10 times that of the base and by 100 times for

pH \ pKa - 2. The base over acid concentration ratio is 10 for pH [ pKa ?1 and 100 for

pH [ pKa ?2.

pH-metry

Exposing aqueous solutions to a corona or a gliding discharge in humid air for time t*

induces a steep pH lowering of the liquid target with the formation of increasing con-

centrations of nitrate ions which continuously increases and nitrite ions which presents a

maximum. The acid effect of such plasma treatment is thus evidenced and mainly

attributed to the formation of nitric acid. The nitrous ions slowly disappear and turn to

nitrates as will be considered below.

In case of a concentrated NaOH solution is exposed to the gliding discharge the

recording of pH vs. t* plots (Fig. 8) is quite similar to the titration plot of a strong base by a

strong acid. The particular exposure time value t*eq corresponding to exact neutralization

(i.e., pH = 7) accounts for the number of protons generated by the discharge and incor-

porated in the solution: t*eq is thus a suitable parameter for checking the efficacy of the

reactor used. It is affected by various working parameters (e.g., the gas flow rate Q, the

electrode gap, the distance between the electrode tips and the liquid surface) and the

experimental conditions (e.g., the concentration and volume of treated solution, in other

words, the number of incorporated OH- ions) in case of a gliding arc device [35]. It is also

governed by the input energy: increasing energy to a given set of working parameters

induces a decay of t*eq which trends to a plateau before increasing. Such a behaviour

suggests that the energy range associated with the ‘‘plateau conditions’’ are the most

efficient conditions to generate protons. Increased energy may give rise to a different set of

reactions which prevents or limits the formation of nitric acid.

Table 3 Main acid base systemsinvolved in air plasma treatmentsof water

Reaction: AH = A- ? H? pKa ¼ �log½CA� �CHþ=CAH�

HNO3 ? NO3- ? H? \0 (strong acid completely

dissociated in water)

HONO = ONO- ? H? 3.3

HOONO = ONOO- ? H? 6.8

HO2 = O2- ? H? 4.7

H2O2 = HO2- ? H? 11.75

OH = O- ? H? 11.9


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A matching pH fall is observed when pure water (pH0 & 6.5–7) is exposed to the

discharge. Analysis of the recorded pH vs t* plot shows that the pH decrease is similar to

adding a strong acid to an aqueous medium.

Since most reactions involved in cleaning or removing organic pollutants are acidity

dependent, the presence of buffers was found useful and a series of Phosphate, Carbonates

or Borate containing buffers was proposed [30], the pH of which varied by less than 0.5

unit for 1 h treatment. They involve components that were unaffected by the oxidizing

properties of the plasma. Some examples are gathered in Table 4. Other buffers may be

prepared with different acid: base molar ratios, e.g., 0.2/0.1 or 0.1/0.2 and successfully

used for acidity control [36, 37]. It should be noted that the buffer solutions are always

concentrate. Additionally concentrate solutions of strong acids or bases also allow to fix

acidity for long exposure times [36], as do incorporation of solid basic salts, e.g., CaCO3

contained in powdered oyster shells [37].

The observed acid effects are attributed to the formation in the treated solution of nitric

acid, i.e., a strong acid completely dissociated, which is identified in the solution both by

absorbance analysis and specific tests. Nitrite is also detected as a transient species,

according to a feature in agreement with thermodynamics.

Fig. 8 Typical plots of pH vs. t* for various NaOH (5 10-3 mol L-1) solutions for three diameters D of theair injection nozzle (Volume 125 mL; Humid air flow 545 Lmin-1; Distance electrode- solution 77 mm) [35]

Table 4 Selected buffers foracidity control in air plasmatreatment

Solution volume: 50 mL

Buffers composition (molL-1) Initial pH(t* = 0)

pH after t* = 1 hexposure

H3PO4 (0.1)/NaH2PO4(0.1) 2.16 2.0

NaH2PO4 (0.1)/Na2HPO4(0.1) 6.85 6.56

HBO2 (0.1)/NaBO2 (0.1) 9.09 8.80

NaHCO3 (0.1)/Na2CO3 (0.1) 9.86 9.62

Na2HPO4 (0.1)/Na3PO4 (0.1) 11.7 11.4


123

Effet of the Feed Gas on pH Titration Plots

The influence of the input gas was considered by many authors who investigated the

influence of water on acidifying aqueous solutions. They agree in concluding with a

positive effect of humid gases: the pH fall of NaOH solution is usually shorter with water

containing inlet gases. However, in case of gliding and corona discharges burning over

aqueous targets, evaporation of the liquid is favoured by the impinging gas (i.e., the

‘‘electric wind’’ in case of coronas or the feeding gas for gliding discharges) and prevents

from using really dry gases. Additionally some glidarc reactors are operated ‘‘in open air’’,

i.e., managing the liquid surface directly in contact with the ambient atmosphere. This

feature means that the inlet gas flow is also in contact with ambient atmosphere and drives

along the components to the liquid surface.

Conductometry Measurements [7, 38, 39]

Many authors interested in performing conductometry measurements on water exposed to

an electrical discharge. The preliminary experiments concern a dc point -to- ring corona

discharge burning in nitrobenzene saturated air over a nitrobenzene (C6H5–NO2) target

[38]. The particular fitting of the earthed ring electrode allowed to trap the charged species

and separate the neutral ones that could reach the liquid surface. The selected liquid is a

polar, low permittivity constant solvent (er = 35.7 Fm-1) which is poorly miscible with

water (S = 15.43 mmol L-1), usually considered as a better solvent for molecules than for

ions. Exposure to the discharge induced a drastic increase in the conductivity of the liquid

with the exposure time. This surprising result demonstrates that the liquid enriches with

ions, and in that case suitable candidates such as NO? or nitrocarboxylates can be guessed,

because water cannot be considered as a determining reagent.

Other conductometry measurements of aqueous solutions exposed to a glidarc discharge

and involving pulsed or not discharges were published [7, 39]. The formation of nitrate is

considered for both treatments and strongly depends on the injection system of the liquid

target and linearly increases with the number of passes (which means that the post-dis-

charge times are partly included in the time base). It is also striking to note that (1) the

occurrence of nitrite is not evidenced, (2) the formation of nitrate is not observed when

Helium or Oxygen are the feed gases, (3) CNO3– is a linear increasing function of the

number of passes (or the exposure time to the discharge).

On treating their conductometry data in connection with pH measurements, the authors

claim that the stoichiometry ratio of nitrate to protons is approximatively 1:1 in case of

oxygen and helium while it is closer to 5 when using air or nitrogen. This discrepancy

suggests that other nitrogen derivatives form in the discharge, such as peroxynitrous acid

(which is claimed to be a weak acid, pKa = 6.9) and behave as transient species.

Oxidizing Properties

The oxidizing properties of most of the plasma species of interest mentioned above are

well known, and widely used for environmental applications, such as pollutant abatement.

Table 5 gathers the standard oxidation potentials E�(Ox/Red) at pH = 0 and room tem-

perature and illustrate the highly oxidizing character of these species: for example their

standard potential is largely higher that 1.23 V/SHE, i.e., the standard potential of the O2/

H2O system.


123

Most of the oxidation/reduction reactions involving organic compounds depend on the

local acidity. Relevant typical equilibria are given by:

Oxþ qHþ þ ne� ¼ Red

which are governed by the Nersnt ‘s law, as already mentioned:

E0 Ox=Redð Þ ¼ E� Ox=Redð Þ þ 2:303 RT=nFð Þ log aOx � aHþq=aRedð Þ

where ai refers to the activity of species i, which is close to the concentration Ci for diluted

solution. For equal concentrations in Ox and Red, the formal oxidation potential E’(Ox/

Red) is usually pH dependent:

E0 Ox=Rdð Þ ¼ E� Ox=Redð Þ � 2:303 RT=nFð Þ q pH:

E’(Ox/Rd) identifies with the standard potential E�(Ox/Red) for pH = 0.

Table 5 Values of standard potentials E�, V/SHE of selected oxidizer/reducer systems

Oxidizer ? qH? ? ne- = Reducer E�(Ox/Red),V/SHE

Oxidizer ? qH? ? ne- = Reducer E�(Ox/Red),V/SHE

OH ? H? ? e- = H2O 2.85 H2O2 ? 2H? ? 2e- = 2H2O 1.76

Ogas ? 2H? ? 2e- = H2O 2.43 ONO2- ? 2H? ? e- = NO2 ? H2O 2.44

O3 ? 2H? ? 2e- = O2 ? H2O 2.07 ONO2H ? H? ? e- = NO2 ? H2O 2.05

O3 ? 6 H? ? 6e- = 3 H2O 1.51 NO? ? e- = NO 1.21

O2 ? 4H? ? 4e- = 2 H2O 1.23 NO2 ? H? ? e- = HNO2 1.09

O2 ? 2H? ? 2e- = H2O2 0.69 NO2 ? 2H? ? 2e- = NO ? H2O 1.05

HO2 ? H? ? e- = H2O2 1.44 NO3- ?3H? ?2e- = HNO2 ? H2O 0.96

HO2 ? 3H? ? 3 e- = 2 H2O 1.63 NO3- ? 4H? ?3e- = NO ? 2H2O 0.94

Fig. 9 Variation of the formal oxidation potential E’� (V/SHE) vs pH relevant to the systems ofinterest:�OH/H2O (dashed grey line); H2O2/H2O (dotted line); ONOOH/NO2 and ONOO-/NO2 (forpH \ 6.9 and pH [ 6.9 respectively) in black lines


123

For example Fig. 9 illustrates the variations of the formal standard potentials of the

systems peroxynitous acid (and peroxynitrite)/NO2 and H2O2/H2O additionally to the

�OH/H2O couple. The E’� values are much higher than 0.5 V/SHE which is the mean

value for the oxidation potential of most organic systems. Examination of these plots

show that �OH, ONOOH/ONOO- and H2O2 easily degrade organic molecules, such as

organic wastes, components of bacterial membranes or living matter. For example, the E�value for the Cytochrome c acid CyFeIIIH?/HCyFeII (pKa of the oxidized forms

CyFeIIIH?/CyFeIII: 9.4) and dehydroascorbate/ascorbate systems (pKas of ascorbic acid:

4.17 and 11.57) are respectively 0.37 and 0.387 V/SHE and the corresponding values E’�at pH = 7, i.e., 0.37 and 0.08 V show that over the whole range of acidity, the reduced

forms of the organic solutes are oxidized by the plasma species. For example, the two

OH substituents at the ethylenic bond of ascorbic acid are oxidized into a-diketone via a

2H?/2e- process. The scheme (Fig. 9) clearly shows that peroxynitrous acid and its

matching base thermodynamically behave as strong oxidizers in a way similar to the

hydroperoxide system. The oxidizing power of peroxynitrous acid and peroxynitrite is

clearly illustrated by the plots of the formal potentials vs pH (Fig. 9) which shows that

the system ONOOH/NO2 is by about 1 V only lower than �OH/H2O ans is a stronger

oxidizer than H2O2/H2O.

The chemical properties of peroxynitrite and the matching acid strongly suggest that

they should act as the major agents implied in the chemical actions of the discharges in air,

in particular for the abatement of organic pollutants. Figure 9 also shows that hydrogen

peroxide is also a potential partner of ONOOH; however H2O2 usually reacts rather slowly,

a feature that leads to kinetic considerations. The remaining questions to be considered are

thus: (1) an extra aspect of the reactivity, namely radical reactions, which are more tightly

concerned with bacterial inactivation and (2) the kinetic aspect of the reactivity of these

species. A matching paper is concerned with these questions.

We have now to cast a look at the specific methods intended to evidence and quantify

the Reactive Nitrogen Species.

Analytical Characterization of Peroxynitrous Acid and its Salt

This section is devoted to the analytical characterization of peroxynitrous acid or

peroxynitrite.

The absorbance spectra of HONOO- and HONOOH presents absorption bands at

302 nm (e = 1,670 L mol-1cm-1) and 270 nm respectively. However absorbance spec-

trophotometry examination of plasma treated solutions for the quantitative determination

of ONOOH and ONOO- is a not fully reliable method because the signals of the transient

species may interfere with peaks at 304 nm (e = 7.1 L mol-1cm-1) and 360 nm (e = 22.5

L mol-1cm-1) relevant to nitrate and nitrite respectively. However, a qualitative test of the

presence of ONOOH is given by the colour change to yellowish by adding a strong base to

the solution.

The specific determination of peroxynitrite and the acid also fails when using poten-

tiometry measurements because potentiometry provides no reliable measurements because

of the position of the the solvent wall at a potential lower than the RNS system. Other usual

techniques require coloured indicators which are not specific to peroxynitrite due to

interference with other strong oxidizers. Koppenol et al. [40, 41] report on both the acidity

constant pKa = 6.8 for ONOOH/ONOO- and an estimate value for the formal potential at

pH:7, i.e., E’� = 1.4 V. The relevant standard potentials are thus calculated as 2.05 and


123

2.44 V/SHE for the systems ONOO-/NO2 and ONOOH/NO2. An immediate consequence

is that both compounds are able to oxidize and degrade the most selective coloured

indicators known, such as indigo derivatives (e.g., indigotrisulfonate) commended for

ozone analysis.

Very recently other analytical techniques were suggested [42, 43], on the basis of the

chemical action of peroxynitrite with suitable compounds, e.g., hemoglobine or carbonate,

and fluorescence methods were used on that occasion.

Conclusions

The main active species formed in non-thermal plasmas are listed with emphasize on the

acid/base and oxidation/reduction properties which govern the plasma-chemical treatments

of organic solutes in aqueous solutions, especially in case of waste treatments. The oxi-

dizing action of the plasma species is attributed to H2O2 and to Reactive Nitrogen Species.

The rapid formation of nitrite which is later followed by its conversion into nitrate

(resulting from the formation of strong nitric acid) is proposed and involves peroxynitrite

as an intermediate.

It is then reasonable to wonder about the actual occurrence of the ONOOH/ONOO-

compounds. Apart spectral identification discussed above, three strong additional argu-

ments support their occurrence namely (1) a discrepancy in the balance of conductimetry

measurements when considering HNO3 as the main source of ions in treated pure water, (2)

the kinetic evolution of the NO2- concentration in aqueous targets and (3) the action of the

plasma species on living matter, with the lethal effect on living micro-organisms (e.g.,

inactivating planktonic, spores and yeasts as well as moistures). The kinetic evolution of

the systems—and especially in view of bacterial inactivation is a crucial question devel-

oped in a matching paper.

References

1. Czernichowski A (1994) Gliding arc: applications to engineering and environmental control. Pure ApplChem 66:1301–1310

2. von Engel A (1965) Ionized gases, 2nd edn. Clarendon Press, Oxford, p 2233. Kamgang-Noubissi JO (2005) Modification des proprietes physicochimiques des surfaces de materiaux

par plasma d’arc glissant d’air humide (in French); PhD Dissertation, Universities of Rouen (France)and Yaounde I (Cameroon)

4. Brisset J-L, Moussa D, Doubla A, Hnatiuc E, Hnatiuc B, Kamgang YG, Herry J-M, Naıtali N, Bellon-Fontaine M-N (2008) Chemical reactivity of discharges and temporal post-discharges in plasmatreatment of aqueous media: examples of gliding discharges treated solutions. Ind Eng Chem Res47:5761–5781

5. Malik MA (2010) Water purification by plasmas: which reactors are most energy efficient ? PlasmaChem Plasma Process 30:21–31

6. Bruggeman P, Leys C (2009) Non-thermal plasmas in and in contact with liquids. J Phys D Appl Phys42:053001

7. Burlica R, Locke BR (2008) Pulsed plasma gliding arc discharges with water spray. IEEE Trans IndAppl 44:482

8. Benstaali B, Boubert P, Cheron B, Addou A, Brisset J-L (2002) Density and rotational temperaturemeasurements of the NO and OH radicals produced by a gliding arc in humid air and their interactionwith aqueous solutions. Plasma Chem Plasma Process 22:553–571

9. Delair L, Brisset J-L, Cheron B (2001) Spectral, electrical and dynamic analysis of a 50 Hz air glidingarc. J High Temp Mater Process 5:381–402


123

10. Allosi M, Dunn M, Livada J, Kirschner K, Shields G (2006) Do hydroxyl radical-water clusters,OH(H2O)n, exist in the atmopshere? J Phys Chem A 110:13286–13289

11. Rabani J, Matheson M (1964) Pulse radiolytic determination of pK for hydroxyl ionic dissociation in theradiation chemistry of water. J Am Chem Soc 86:3175

12. Sehested K, Holeman J, Hart E (1983) J Phys Chem 87: 1951 (cited in Getoff N. - Peroxyl Radicals inthe treatment of waste solutions. In: Alfassi Z (ed) Peroxyl radicals (1997) J. Wiley & Sons, Chichester,UK. Chap. 16)

13. Wallington T, Nielsen O, Schested J (1997) Reactions of organic peroxyl radicals in the gas phase. In:Alfassi Z (ed) Peroxyl radicals, Chap 7. Wiley, Chichester

14. Sehested K, Holeman J, Bjergbakke E, Hart E (1984) J Phys Chem 88: 4144 (cited in N. Getoff -Peroxyl Radicals in the treatment of waste solutions. In: Alfassi Z (ed) Peroxyl radicals (1997) J. Wiley& Sons, Chichester, UK. Chap. 16)

15. Buxton G, Greenstock C, Helman W, Ross A (1988) J Phys Chem Ref Data 17:51316. Katsumura Y (1998) NO2 and NO3 radicals in radiolysis of nitric acid solutions. In: Alfassi Z (ed) N

centered radicals, Chap 12. Wiley, Chichester, pp 393–41217. Elsayed N (1998) Toxicity of nitrogen oxides. In: Alfassi Z (ed) N centered radicals, Chap 6. Wiley,

Chichester, pp 181–20618. Dorthe G (1998) Reactions of NO in the gas phase. In Alfassi Z (ed) N centered radicals, Chap. 1.

Wiley, Chichester, pp 1–3819. Warman P (1998) Nitrogen dioxide in biology: correlating chemical kinetics and biological effects. In:

Alfassi Z (ed) N centered radicals, Chap. 5. Wiley, Chichester, pp 155–18020. Kannan K, Udayakumar M (2009) Modeling of NO formation in single cylinder direct injection Diesel

engine using Diesel-Water emulsion. Am J Appl Sci 6:1313–132021. Atkinson R, Baulch D, Cox R, Hampson R, Kerr J, Troe J (1992) Evaluated kinetic and photochemical

data for atmospheric chemistry; supplement IV. J Phys Chem Ref Data 21:112522. Brisset J-L, Dubreuil N, Lelievre J (1995) Electrolysis reactions in a d.c. Corona discharge in humid air.

Pol J Appl Chem XXXIX z4:557–57123. Abdelmalek F (2003) Plasmachimie des solutions aqueuses. Application a la degradation de composes

toxiques (in French); Plasmachemistry of aqueous solutions; Application to the removal of harmfulcompounds. PhD. Dissertation, Mostaganem University, Algeria

24. Halfpenny E, Robinson PL (1952) Pernitrous acid. The reaction between hydrogen peroxide and nitrousacid, and the properties of an intermediate product. J Chem Soc 928–938

25. Edwards JO, Plumb RC (1994) The chemistry of peroxonitrites. In: Progress in inorganic chemistry, vol41. Wiley, Chichester, pp 599–635

26. Pannala A, Singh S, Rice-Evans C (1999) Interaction of carotenoids and tocopherols with peroxynitrite.In Packer L (ed) Methods in enzymology, vol. 301-C, Chap. 34. Academic Press, London, pp 319–332

27. Ceballos-Picot I, Blum D, Ramassamy C, Przedborski S (2005) Le stress oxydant dans les processusneurodegeneratifs et la mort neuronale: cause ou consequence? In: Delattre J, Beaudeux JL, Bonnefont-Rousselot D (eds) Radicaux libres et stress oxydant, Chap. 15. Tec&Doc Lavoisier, Paris, pp 429–474

28. Seago N, Clark D, Miller M (1995) Role of inducible nitric oxide synthase (iNOS) and peroxynitrite ingut inflammation. Inflamm Res 44(Supp 2):S153–S154

29. Heinecke J (2002) Oxidized amino acids: culprits in human atheroscleriosis and indicators of oxidativestress. Free Rad Biol Med 32:1090–1101

30. Pannala AS, Rice-Evans C, Halliwell B, Singh S (1997) Inhibition of peroxynitrite mediated tyrosinenitration by catechin polyphenols. Biochem Biophys Res Comun 232:164–168

31. Pryor W, Squadrito G (1995) The chemistry of peroxynitrite: a product from the reaction of nitric oxidewith superoxide. Am J Physiol 268:L699–L722

32. Goldstein S, Czapski G (1995) The reaction of NO� with O2�-: a pulse radiolysis study. Free Rad BiolMed 19:505–510

33. Huie R, Padmaja S (1993) Reaction of �NO with O2�-. Free Rad Res Commun 18:195–19934. Ischiropoulos H, Zhu L, Beckman J (1992) Peroxynitrite formation from macrophage derived nitric

oxide. Arch Biochem Biophys 298:446–45135. Benstaali B, Moussa D, Addou A, Brisset J-L (1998) Plasma treatment of aqueous solutes: some

chemical properties of a gliding arc in humid air. Euro Phys J Appl Phys 4:171–17936. Moussa D, Abdelmalek F, Benstaali B, Addou A, Hnatiuc E, Brisset JL (2005) Acidity control of the

oxidation reactions induced by non-thermal plasma treatment of aqueous effluents in pollutant abate-ment processes. Euro Phys J Appl Phys 29:189–199

37. Brisset J-L, Benstaali B, Moussa D, Fanmoe J, Njoyim-Tamungang E (2011) Acidity control of plasma-chemical oxidation: application to dye removal, urban wastes abatement and microbial inactivation.Plasma Sources Sci Technol 20:034021


123

38. Brisset J-L, Dubreuil N, Lelievre J (1995) Electrolysis reactions in a DC corona discharge in humid air.Polish J Appl Chem XXXIX z.4:557–571

39. Porter D, Poplin M, Holzer F, Finney W, Locke BR (2009) Formation of hydrogen peroxide, hydrogenand oxygen in gliding arc electrical discharge reactors with water spray. IEEE Trans Ind Appl45:623–629

40. Koppenol W, Moreno J, Pryor W, Ischiropoulos H, Beckman H (1992) Peroxynitrite, a cloaked oxidantformed by nitric oxide and superoxide. Chem Res Toxicol 2:834–842

41. Koppenol W (1998) The basic chemistry of nitrogen monoxide and peroxynitrite. Free Rad Biol Med25:385–391

42. Liu C, Lin J-M, Huie C, Yamada M (2004) Chimiluminescence study of carbonate and peroxynitrousacid and its application to the direct determination of nitrite based on solid surface enhancement.Analytica Chim Acta 510:29–34

43. Liang J, Liu Z-H, Cai RX (2005) A novel method for determination of peroxynitrite based on hemo-globine catalyzed reaction. Analytica Chim Acta 530:317–324


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Peroxynitrite: A Re-examination of the Chemical Properties of Non-thermal Discharges Burning in Air...

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