CHAPTER –I

INTRODUCTION TO OZONE

1.1 Introduction

In the recent past climate change and environmental problems are the major

global issues. The green house gases loading, aerosol loading, ozone depletion,

increasing surface ozone, acid rains are the major environmental problems to the

scientific society. Ozone acts as a beneficial one or harmful depends on the

concentration where it is located. Recently, researchers showed that stratospheric

ozone level has been decreasing in significant level, at the same time due to industrial

and transport activities surface ozone has been increasing. Increasing ozone level

changes the climate through both direct and indirect routes. Since ozone is involved

in climate changes, it is necessary to study the ozone and its measurement in the

present time. Ozone is a secondary photochemical pollutant [1, 2]. Elevated levels

cause health problems, premature deaths, reduced agricultural crop yields, changes in

ecosystem species composition and damage to physical infrastructure and cultural

heritage.

1.2 Ozone and its structure

Ozone is a minor constituent of the atmosphere. It is a form of oxygen. It is an

odorless, colorless gas. At the molecular level, ozone is made up of three oxygen

atoms (O3) with one double bond and one single bond. Normal oxygen, which we

breathe, has two oxygen atoms and is colorless and odorless. Ozone, or triatomic

oxygen, is much more unstable than diatomic oxygen found in air and is therefore a

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strong oxidizing agent. Ozone was discovered by C.F.Schönbein in the middle of the

last century; he also was first to detect ozone in air [3, 4]. Ozone is much less

common than normal oxygen. Out of each 10 million air molecules, about 2 million

are normal oxygen, but only 3 are ozone. Ozone exits in the atmosphere at two

heights. They are starostocpheric ozone and tropospheric ozone. Fig 1.1 shows

structure of ozone.

Fig 1.1- Ozone Structure

1.3 Ozone in Atmosphere

Ozone is important in two layers of the atmosphere. Most ozone (about 90%)

resides in a layer between approximately 10 and 50 km above the Earth’s surface, in

the region of the atmosphere called the stratosphere. Roughly 10% of the Earth's

ozone is found in the lower region of the atmosphere, in the region of the atmosphere

called, troposphere. Most ozone is produced naturally in the upper atmosphere or

stratosphere. While ozone can be found through the entire atmosphere, the greatest

concentration occurs at an altitude of about 25 km [5]. This band of ozone-rich air is

known as the "ozone layer". The stratosphere ranges from an altitude of 10km to

50km and it lies above the troposphere (or lower atmosphere). Even though both

types of ozone are exactly the same molecule, their presence in different parts of the

atmosphere has very different consequences. Stratospheric ozone blocks harmful

solar radiation - all life on Earth has adapted to this filtered solar radiation.

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Stratospheric ozone shields us from the harmful effects of the Sun's ultra-violet

radiation. Fig 1.2 shows ozone in atmosphere.

Fig 1.2 - Ozone in atmosphere

1.4 Why is the ozone layer important?

Ozone's unique physical properties allow the ozone layer to act as our planet's

sunscreen, providing an invisible filter to help protect all life forms from the Sun's

damaging ultraviolet (UV) rays. Most incoming UV radiation is absorbed by ozone

and prevented from reaching the Earth's surface. Without the protective effect of

ozone, life on Earth would not have evolved in the way it has.

1.5 Ozone measurement units

Various units are used to measure surface ozone. The most common surface

ozone measurement is ppm, and is used to measure ozone in air and ozone dissolved

into water.

(i) ppm = parts per million is a measurement of concentration. If we state there is 1

ppm ozone that means for every 1 million parts of gas, 1 of these is ozone.

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(ii) ppb = parts per billion. For example 0.1 ppm = 100 ppb.

(iii) mg/l = milligrams of ozone per liter. This indicates how many milligrams of

ozone there are in one liter of total volume. Mg/l can be used to indicate the

concentration of ozone in gas or liquid. 1 mg/l of ozone = 1 ppm of ozone in

water. Due to the density of air this is no longer true and 1 ppm of ozone = 2140

mg/l. This is a common term used to measure the amount of ozone dissolved into

water.

(iv) µg/ml = microgram per milliliter. This indicates how many micrograms of ozone

there are in one milliliter of total volume. µg/ml can be used to indicate the

concentration of ozone in gas or liquid. 1 µg/ml = 1 mg/l = 1g/m3 = 1 gamma.

(v) G/m3 = Grams of ozone per Cubic Meter is a measurement of concentration.

This indicates how many grams of ozone there are in one cubic meter of total

volume. This can indicate volume of a gas or liquid. g/m3

is most commonly

used to measure the concentration of ozone in a gas stream. 1 g/m3

= 1 mg/l = 1

ppm of ozone in water 1 g/m3

= 467 ppm of ozone in air.

(vi) %by weight (Percent by weight) is a measurement of concentration. This

indicates the percentage (%) of ozone within a given gas stream. This is a very

common method to illustrate the concentration of ozone from an Ozone

Generator. This is more complicated than g/m3

as the weight of gas changes if it

is air, or oxygen gas that the ozone gas is mixed with 1% Ozone = 12.8

g/m3

Ozone in air 1% Ozone = 14.3 g/m3

Ozone in oxygen.

(vii) G/hr (gm/hr) = grams of ozone per hour is a measurement of ozone production.

This is the most common method of measuring the output of an Ozone

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Generator. We can measure the concentration of ozone in g/m3, then when we

calculate for flow rate with a measurement such as LPM (liters per minute), we

can determine how many grams of ozone are produced in one hour of time.

(viii) Mg/hr = milligrams of ozone per hour. This indicates the same thing as g/hr

only on a smaller scale. Smaller Ozone Generators may be rated in mg/hr.1 g/hr

of ozone = 1,000 mg/hr of ozone production.

(ix) Lb/day = Pounds per Day is a measurement of ozone production. This is a

common measurement of ozone production for large Ozone Generators, and is

commonly used in some industries within the ozone world Lb/day of ozone =

18.89 g/hr ozone production.

1.6 The abundance and measurement of ozone levels

The abundance of ozone in the atmosphere is measured by a variety of

techniques as shown in figure 1.3. The techniques make use of ozone’s unique optical

and chemical properties. There are two principal categories of measurement

techniques: local and remote. Ozone measurements by these techniques have been

essential in monitoring changes in the ozone layer and in developing our

understanding of the processes that control ozone abundances.

1.6.1 Local measurements

Local measurements of atmospheric ozone abundance are those that require

air to be drawn directly into an instrument. Once inside an instrument, ozone can be

measured by its absorption of ultraviolet (UV) light or by the electrical current

produced in an ozone chemical reaction. The latter approach is used in the

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construction of “ozonesondes,” which are light weight. Ozone measuring modules are

suitable for launching on small balloons. The balloons ascend far enough in the

atmosphere to measure ozone in the stratospheric ozone layer. Local ozone-

measuring instruments using optical or chemical detection schemes are also used

routinely on board research aircraft to measure the distribution of ozone in the

troposphere and lower stratosphere.

1.6.2. Remote measurements

Remote measurements of ozone abundance are obtained by detecting the

presence of ozone at large distances away from the instrument. Most remote

measurements of ozone rely on its unique absorption of UV radiation. Sources of UV

radiation that can be used are the Sun and lasers. For example, satellites use the

absorption of UV sunlight by the atmosphere or the absorption of sunlight scattered

from the surface of Earth to measure ozone over nearly the entire globe on a daily

basis. A network of ground-based detectors measures ozone by the amount of the

Sun’s UV light that reaches Earth’s surface. Other instruments measure ozone using

its absorption of infrared or visible radiation or its emission of microwave or infrared

radiation. Total ozone amounts and the altitude distribution of ozone can be obtained

with remote measurement techniques. Lasers are routinely deployed at ground sites or

on board aircraft to detect ozone over a distance of many kilometers along the laser

light path.

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Fig 1.3-Ozone measured by various instruments techniques

1.7 The Formation of Stratospheric Ozone

Ozone is created in the stratosphere when highly energetic solar radiation

strikes molecules of oxygen (O2) and cause the two oxygen atoms to split apart. If a

freed atom bumps into another O2, it joins up, forming ozone (O3). This process is

known as photolysis. Fig1.4 refers ozone formation in stratosphere. Ozone is also

naturally broken down in the stratosphere by sunlight and by a chemical reaction with

various compounds containing nitrogen, hydrogen and chlorine. These chemicals all

occur naturally in the atmosphere in very small amounts. In an unpolluted atmosphere

there is a balance between the amount of ozone being produced and the amount of

ozone being destroyed. As a result, the total concentration of ozone in the

stratosphere remains relatively constant. At different temperatures and pressures (i.e.

varying altitudes within the stratosphere), there are different formation and

destruction reaction rates. Thus, the amount of ozone within the stratosphere varies

according to altitude. Ozone concentrations are highest between 19 and 23 km.

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Fig 1.4–Stratospheric ozone production

1.8 Effect of climate change on stratospheric ozone

Climate change affects stratospheric ozone in two principal ways. The first is

through in-situ hanges within the stratosphere, from radiative-chemical mechanisms,

associated with the changes in anthropogenic greenhouse gases (for the stratosphere,

this is mainly from the changes in carbon dioxide).The second is through changes in

stratospheric wave forcing and hence in the Brewer-Dobson circulation which result

from changes in tropospheric climate. That the latter has the potential to be a

significant contributor is evident from the contrast between the two hemispheres in

the current climate, which results from differences in wave forcing. Whilst in the real

atmosphere these two processes occur together and cannot be isolated, in a model

they can be. In doubled-CO2 experiments with chemistry-climate models, [6]

separated the two processes by doubling CO2 separately in the troposphere and the

stratosphere, while [7] and [8] instead did so by separately doubling CO2 and making

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the corresponding changes to sea surface temperatures and the associated sea ice

distributions.

Climate change may cause an increase in temperature in the troposphere and a

decrease in temperature in the stratosphere. This decrease may delay the recovery of

the ozone layer at the Arctic and Antarctic by several years, due to an increase in

clouds in the stratosphere. The greenhouse gases methane and nitrous oxide may also

affect stratospheric ozone by chemical interactions. This may have a positive or

negative effect [9]. The magnitude of this interaction is uncertain and depends on the

emissions of methane and nitrous oxide and the chlorine concentration. Aircraft emit

nitrogen oxides (NOx) directly in the upper troposphere and lower stratosphere. This

is the only anthropogenic source of NOx in these regions. The impact of the current

fleet of aircraft on the observed ozone depletion is unknown but probably small. The

effect of a possible future fleet of supersonic aircraft flying in the stratosphere on the

ozone layer could be slightly negative, but with a considerable uncertainty range

[10, 11].Increases in UV-B due to depletion of ozone in higher level may affect the

growth, photosynthesis and reproduction of phytoplankton. Reductions in

phytoplankton may result in a reduced uptake of CO2 in the oceans [12].

1.9 Radiative force- use of climate change prediction

Radiative forcing is a measure of how the energy balance of the Earth-

atmosphere system is influenced when factors that affect climate are altered. The

word radiative arises because these factors change the balance between incoming

solar radiation and outgoing infrared radiation within the Earth’s atmosphere. This

radiative balance controls the Earth’s surface temperature. The term forcing is used to

indicate that Earth’s radiative balance is being pushed away from its normal state.

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Radiative forcing is usually quantified as the ‘rate of energy change per unit area of

the globe as measured at the top of the atmosphere’, and is expressed in units of

‘Watts per square metre’. Ramaswamy[13] defines it as ‘the change in net (down

minus up) irradiance (solar plus long wave; in Wm-2

) at the tropopause after allowing

for stratospheric temperatures to readjust to radiative equilibrium, but with surface

and tropospheric temperatures and state held fixed at the unperturbed values’. When

radiative forcing from a factor or group of factors is evaluated as positive, the energy

of the Earth-atmosphere system will ultimately increase, leading to a warming of the

system. In contrast, for a negative radiative forcing, the energy will ultimately

decrease, leading to a cooling of the system.

Radiative forcing can be related through a linear relationship to the global

mean equilibrium temperature change at the surface (ΔTs):

ΔTs = λRF ( 1.1)

Where λ is the climate sensitivity parameter.

(1.2)

This equation, developed from these early climate studies, represents a linear view of

global mean climate change between two equilibrium climate states. Radiative

forcing is a simple measure for both quantifying and ranking the many different

influences on climate change; it provides a limited measure of climate change as it

does not attempt to represent the overall climate response.

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1.9.1 Radiative forcing for important green house gases

The important green house gases radiative forcing are shown in table 1.1

Table 1.1 Radiative forcing for green house

Trace gas Simplified Expression Radiative forcing,

ΔF(Wm-2

)

Constants

CO2

ΔF = α*+,-.-)/

ΔF= α*+,-.-)/0 1, /

ΔF = α,2,-/32,-)//

4567682,-/9*+,(0(: -0):))#- 0(:";()

3$-!/

α =5.35

α=4.841,

19):)')$

α=3.35

-<" ΔF= α, /3,=,>8?@A/ 3 =,>A ?@A// α =0.036

@ B ΔF= α, /3,=,>A ?@/ 3 =,>A ?@A// α =0.12

-C-3((!

ΔF = α(X-Xo) α =0.25

-C-3( ΔF = α (X-Xo) α =0.32

F(M,N)=0.47 ln[1+2.01X10-5

(MN)0.75

+5.31X10-15

M(MN)1.52

] (1.3)

Where C is CO2 in ppm, M is CH4 in ppb, N is N2O in ppb,X is CFC in ppb

The constant in the simplified expression for CO2 for the first row is based on

radiative transfer calculations with three-dimensional climatological meteorological

input data [14]. For the second and third rows, constants are derived with radiative

transfer calculations using one-dimensional global average meteorological input data

from [15,16] respectively. The subscript 0 denotes the unperturbed concentration. The

same expression is used for all CFCs and CFC replacements.

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Fig 1.5- Global mean radiative force values

For tropospheric ozone,

(ΔT2X)O = GO(ΔF2X) .. . . . (1.4)

Where GO = T/ (1-αp) So is the gain of the climate system with zero feedback

[16,17,18]. Taking the global-mean temperature T= 288K, planetary albedo αp= 0.3,

and solar irradiance So = 1367 Wm-2

yields GO = 0.3oC /Wm

-2.For ΔF2X =3.71 Wm

-2,

ΔT2X =1.12oC.

Total radiative forcing at time” t” [19], then

(1.5)

equation (1.5) assumes that the development of total radiative forcing is proportional

to radiative forcing due to carbon dioxide. Scaling parameter ω is a measure for the

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relative contribution of CO2 (1/ω is the share of CO2). Fig 1.5 shows global mean

radiative force values.

1.9.2 Direct and Indirect Radiative Forcing Agents:

Direct radiative forcing agents are emitted into the atmosphere and force the

climate system directly. Indirect radiative forcing agents act on the global

distributions of methane and tropospheric ozone and force the climate system

indirectly. Tropospheric ozone precursors such as VOCs, CO, H2, NOx are indirect

radiative forcing agents. Methane also acts as an indirect radiative forcing agent

although it is also a direct radiative forcing agent.

OH + VOC = RO2 (1.6)

RO2 + NO = NO2 + products (1.7)

NO2+ sunlight =NO +O3 (1.8)

NO+HO2=NO2+OH (1.9)

OH+CH4=products (1.10)

1.9.3 Gases: Hydroxyl Radical (OH): The detergent of the

atmosphere

OH is a major tropospheric oxidant. It removes CO/VOCs, is involved in

tropospheric ozone (O3) production, and in aerosol formation. It is the major sink of

CH4 in the atmosphere: OH determines CH4 lifetime. Multi-model OH highest in low

latitudes, especially over polluted regions. Changes in the future mostly negative, due

to large methane increases (sink) in this drastic scenario.

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1.9.4 Aerosols: major components

Sulphate (SO4) (anthropogenic and natural; natural comes mainly from

oceans and volcanoes). Black carbon (BC) (mostly anthropogenic; also from natural

fires). Organic carbon (anthropogenic and natural; natural comes from secondary

aerosol formation above forests). Mineral dust (mainly natural). Sea-salt (natural)

Nitrate (both anthropogenic and natural). Sulphate particles are produced from gases

(through OH oxidation) in the atmosphere. Their main precursors are:

a) anthropogenic or volcanic sulphur dioxide (SO2), b) dimethyl sulfide (DMS) from

biogenic sources, especially marine plankton. Sulphate is mostly scattering (cooling).

Black carbon is emitted in aerosol form (no gas precursors). It mainly comes from

fossil fuel combustion and biomass burning. BC is mostly absorbing (warming).

1.9.5 Drawback of Global radiative force in the case of aerosol and

surface ozone

Global radiative force forcing is not always useful, as: Temperature response

depends on a variety of uncertain feedbacks, and is highly region-dependent. Many

forcing agents, such as aerosols and tropospheric ozone (short-lived) are very

inhomogeneous, leading to complex patterns of forcing and response. A global view

of composition and radiation from satellites and from composition-climate models

(both recent developments!) can facilitate the study of such problems.

1.10 Stratospheric ozone and Temperature

Stratospheric ozone is not an anthropogenic forcing agent; rather it is (like

water vapour) an internal property of the atmosphere. For example, cooling of the

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upper stratosphere increases ozone abundance, by slowing ozone destruction rates,

and the increased ozone abundance offsets some of the cooling [20,21]. This ozone-

temperature feedback has, therefore, mitigated the upper stratospheric cooling that

would otherwise have occurred from the CO2 changes alone. The primary

anthropogenic forcing agents for past stratospheric ozone and temperature changes

are ozone-depleting substances (ODSs) and CO2 [22]. Because of the ozone-

temperature feedback, the upper stratospheric ozone depletion due to ODSs has been

partially masked by CO2-induced ozone increases. It follows that using the observed

ozone decreases to attribute global mean temperature changes must under estimate

the cooling due to ODSs (via ozone depletion), and overestimate the cooling due to

CO2 increases.

1.11 Stratospheric ozone and rainfall mechanism

Rainfall is an important parameter of our environment. O3 concentration is

maximum at a height of about 25 km above sea level. UV rays contain high-energy

photons which decompose ozone into oxygen. Ozone of the stratosphere absorbs

maximum of the incoming UV photons resulting a warm ozonosphere. But, it resists

the photons to fall directly on the clouds of the troposphere whose maximum height is

about 18 km above from the sea level. Hence it resists the unwanted warming of

cloud by UV rays and the high concentration of ozone in the stratosphere helps heavy

rainfall. The net reaction for the formation of ozone in the stratosphere is given

below:

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O2 + O2 → O3 + O (1.11)

O + O2 + M → O3 + M (1.12)

────────────────

3 O2 → 2 O3 (1.13)

It is shown by Midya [23] that if we consider that the reaction is endothermic,

this helps us to explain the dramatic decrease of ozone concentration over Antarctica

during spring time. So the higher temperature of the stratosphere will favor the higher

equilibrium concentration of ozone. Thus when the temperature of the stratosphere

increases by absorbing solar radiation, this will try to attain higher ozone

concentration of stratosphere. This also helps to attain low temperature of troposphere

and heavy rainfall. When stratospheric ozone is depleted, solar UV ray falls directly

on troposphere. As a result temperature of stratosphere decreases and that of

troposphere increases. This helps to attain an unfavorable condition of rainfall.

Although this is the main mechanism of rain fall, less intense rain (showers) can

occur even when the cloud does not contain ice crystals at all. But, the presence of

CCN is essential for heavy rainfall. One study says that, stratospheric ozone

concentration must be at a certain concentration level in order to obtain sufficient

rainfall. One study says that ozone concentration decreases, monsoon rainfall

increases with time, and monsoon rainfall occurs only when ozone concentration

reaches to a certain concentration level along with other parameters of precipitation.

This level slightly differs from station to station and it confirms latitudinal variations

of ozone concentrations for which rainfall takes place [24]. Monsoon rainfall is a very

complex process. It not only depends on ozone concentration but also on CCN,

humidity, temperature, El-Nino, etc. Monsoon rainfall starts when ozone

concentration reaches to a certain concentration level and monsoon rainfall decreases

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with the increase of ozone concentration. Midya [25] showed that N2O plays

important role in the depletion of stratospheric O3. Decrease of O3 concentrations

over India may be due to the increase of N2O over India.

1.12 Stratospheric ozone and UV radiation

Sunlight consists of solar rays of differing wavelengths. Visible light ranges

from 400nm (violet) to 700nm (red). Infrared radiation, or heat, has longer

wavelengths than visible light; ultraviolet radiation has shorter wavelengths than

visible light. UVR is further divided into UVA (315–400nm), UVB (280–315nm) and

UV-C (<280nm). Almost all incoming solar UVC and 90% of UVB are absorbed by

stratospheric ozone, while most UVA passes through the atmosphere unchanged.

Although UVA penetrates human skin more deeply than UVB, the action spectra

from biological responses indicate that it is radiation in the UVB range that is

absorbed by DNA—subsequent damage to DNA appears to be a key factor in the

initiation of the carcinogenic process in skin. The amount of ambient UVB

experienced by an individual outdoors with skin exposed directly to the sky is

dependent on the following:(i) stratospheric ozone levels(ii) solar elevation(iii)

regional pollution(iv) altitude of the individual(v) cloud cover(vi) presence of

reflective environmental surfaces such as water, sand or snow. Since ozone is not the

only influence on surface UV, and may not be the only parameter to change in the

future, or to have done so in recent years. Clouds can cause large and rapid changes

(increases as well as decreases) in surface UV radiation and in total radiation (i.e.,

radiation integrated over the entire spectrum from about 300 nm to 3000 nm). On

average, clouds have an attenuating effect of 15–32% in the UV wave band [26, 27],

but for any given situation the cloud effect will depend on the cloud type, depth, and

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distribution across the sky. Thus, cloud transmission of UV irradiance is difficult to

quantify in sufficient detail to provide an exact determination of its effect at a given

time and place [28].

Solar uv rays contain high energy photons which decompose water molecules

into atomic oxygen and OH radical. Thus we can expect that it stratospheric ozone is

depleted, the high energy solar uv photon fall directly on troposphere and as a result,

tropospheric water molecules are decomposed resulting the fall of relative humidity

and increase of tropospheric ozone which acts as greenhouse gas and plays important

role in global warming [29].

1.13 Stratospheric ozone and EL NINO

In terms of disturbance, the area is subject to hurricanes and tropical storms

and the increased precipitation and winds from these events. Disturbances most often

arise from (i) cyclonic systems, (ii) noncyclonic inter tropical systems, (iii) extra

tropical frontal systems, and (iv) large- scale, coupled ocean-atmospheric events (e.g.,

North Atlantic Oscillation, El Niño-Southern Oscillation)[30]. Intratropical

atmospheric systems start and stay in the tropics. For large-scale ocean-atmospheric

systems such as the NAO and ENSO, the NAO has the stronger relationship with

PR’s annual climate than ENSO. A high winter NAO is correlated with lower

precipitation in PR. ENSO events are correlated with temperature in the Luquillo

Mountains and associated with wetter conditions from April to July. El Nino is

associated with drier conditions from September to October throughout the

Caribbean. All of these relationships are generally fairly weak, however, and have a

poor link to hurricanes and other large-scale disturbances.

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1.14 Stratospheric ozone and Quasi Biennial oscillation

Stratospheric ozone is produced by ultraviolet photo dissociation of molecular

oxygen and destroyed by catalytic reactions of the oxides of hydrogen, nitrogen,

chlorine, and bromine. The distribution of ozone with latitude, longitude, and altitude

is determined by large and small-scale transport between regions of net production

and regions of net loss. Stratospheric ozone is sensitive to variability in both

photochemical and dynamical processes and thus varies on seasonal and longer time

scales. After accounting for variability due to the seasonal and solar cycle in

ultraviolet flux, variability due to volcanic aerosols, and variability due to dynamic

influence such as the quasi-biennial oscillation(QBO), analysis of observations

indicate a downward trend in stratospheric ozone over the time period from1979 to

the late 1990s [31,32,33]. The growth of reactive chlorine and bromine in the

stratosphere due to decomposition of industrially produced chlorofluorocarbons

(CFCs), halons, and methyl bromide has, over the last two decades, led to a decrease

in the amount of ozone overhead. The statistical analysis accounts for random and

coherent dynamical variability other than the QBO only in the noise term that helps to

evaluate uncertainties.

1.15 The Formation of Tropospheric Ozone

Tropospheric ozone, which is the most important oxidant in the atmosphere, is

formed through in-situ photochemical reactions involving nitrogen oxides and

volatile organic compounds [34-37]. Enhanced levels of tropospheric ozone are a

serious concern because of effects on human health, [38-42] crops, ecosystems,

building materials [43-45] and, hence, the economy [46-51]. Additionally,

tropospheric ozone is the third most important greenhouse gas after carbon dioxide

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and methane [52-53], hence, the increasing trend in tropospheric ozone is influencing

both the chemical composition of the atmosphere and global climate. The main

sources of ozone in the troposphere are: Incursion from the stratosphere. Reactions

involving precursors that come from biogenic volatile organic compounds (VOC);

and, Photochemical reactions with the precursors, nitrogen oxides (NOx = NO +

NO2), carbon monoxide (CO), methane (CH4) and other organic compounds resulting

from anthropogenic activities. It was thought that tropospheric ozone largely resulted

from the processes of stratosphere-troposphere exchange and organic materials

deposition at the Earth’s surface.

As far as the photochemistry is concerned, the formation mechanism is

influenced by the mixing ratio between all the relevant chemical compounds (for

example, precursors and oxidants). Otherwise, an important factor related to ozone

formation is solar radiation with a wavelength range of around 320nm to 410nm [54].

A general process of ozone formation at the boundary layer can be written as follows

[55]:

NOx + NMHCs + hν+ M (N2, O2) → O3 + other photochemical oxidants (1.14)

(NMHCs = non methane hydrocarbons, hν= ultraviolet solar radiation,

320nm~ 410nm, and other terms have been defined above).

A conversion reaction of NOx should be noted, involving a catalytic cycle of

ozone formation and consumption. The cyclic reactions are as follow:

NO2 + hν→ O + NO (1.15)

O + O2 + M → O3 + M (M = N2, O2) (1.16)

O3 + NO → O2 + NO2 (1.17)

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The major physical mechanisms affecting tropospheric ozone formation include local

meteorological conditions (such as humidity, temperature, wind speed and direction)

[56, 57]. For instance, low humidity, low wind speeds, calm weather and cloud-free

conditions favour the photochemical reactions. Therefore, the precursors and ozone

from the vicinity could bring more serious effects on the air quality. The lifetime of

ozone in the troposphere is typically a few weeks [58].

1.15.1 National Ambient Air Quality Standards for ozone

Ambient standards and guidelines for ground-level ozone or surface ozone are

aimed at protecting human health, sensitivity ecosystems, and agricultural plants from

the harmful effects of ground-level Ozone. Final rules signed June 2010. National

Ambient Air quality standard had attained by using three year average of the daily

maximum one hour average value and each value must not exceed 75 ppb

(0.075ppm).Table 1.2 gives the prescribed values of surface level ozone as per

National Ambient Air Quality Standards.

Table 1.2. National Ambient Air Quality Standards (NAAQS)

Pollutant Level Averaging Time

Ozone

0.075 ppm

(2008 std) 8-hour

0.08 ppm

(1997 std) 8-hour

0.12 ppm 1-hour

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1.16 Tropospheric ozone and Clouds

Clouds are condensed atmospheric moisture in the form of minute water

droplets or ice crystals. Formation and destruction of ozone in the troposphere

comprises a series of complex cycles in which atomic oxygen, molecular oxygen,

carbon monoxide, oxides of nitrogen, water vapour, volatile organic compounds, etc.

are involved. Ozone in the troposphere is produced by the addition of ground state

oxygen atoms O (3p) to molecular oxygen assisted by any third body M to ensure

simultaneous momentum and energy conservation [59].

O3p_+O2 +M → O3 +M. (1.18)

The primitive terrestrial atmosphere was oxygenic in nature and ozone was produced

by photo dissociation of water vapour as follows [60].

H2O+hν → OH + H (1.19)

OH + hν → O+H (1.20)

O+O+M → O2+M (1.21)

O+O2 +M → O3 +M (1.22)

1.17 Tropospheric ozone and temperature, Humidity

Temperature, atmospheric humidity and sunshine levels influence background

O3 levels through the controls they exert on the photochemistry of net O3 production.

Temperature is often used as a predictor for high O3 [61, 62]because of its direct

influence on chemical kinetic rates and the mechanism pathway for the generation of

O3 [e.g., H-abstraction versus OH addition [63] and strong correlation with stagnant,

sunny atmospheric conditions .Higher temperatures accelerate O3 production

(depending on the NOX regime), and especially in summer, are also likely to increase

biogenic VOC emissions and hence lead to higher surface O3 concentrations in high

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NOX regions. Temperatures are expected to increase more over the continents than

the oceans. The chemistry of O3 production, initiated by reactions of OH with CH4,

CO and VOC. OH is produced following photolysis of O3 in the presence of water

vapour, therefore absolute humidity is a strong determinant of background O3 levels,

and the expected changes in atmospheric humidity associated with global warming

are likely to have complex effects on surface O3.

1.18 Tropospheric Ozone and ENSO

The dramatic variation of seasonal distributions of high ozone days seems to

be related to short-term variation of climate that might result from the effect of El

Niño Southern Oscillation (ENSO). McPhaden [64] indicated that the year 1997-1998

was the strongest El Niño phenomenon on record and followed by an extended La

Niña period that began in mid-1998 to the winter of 2000 and slowly decayed from

the spring of 2001. The interplay between the Asian winter monsoon and ENSO plays

an influential role in East Asian climate. The linkage between the climate of East

Asia and ENSO has been found, for example, a weaker East Asian winter monsoon

along the East Asian coast occurs during the mature phase of ENSO and the

relationship between the rainfall patterns and ENSO. Nevertheless, the effects of La

Niña on climate show a reverse situation, especially in equatorial region [65].

1.19 Tropospheric ozone and Lightning

Roughly 10% of the ozone in the troposphere plays a key role in providing

oxidizing radicals, OH that cleanses the lower atmosphere of pollutants, such as

carbon monoxide (CO), and sulfur dioxide (SO2). Global NOx (NO+NO2) has various

sources, including fossil fuel combustion, biomass burning, aircraft emission,

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microbial processes in the soil, and lightning .Nitric oxide is produced in the hot

lightning channel by way of the Zel’dovich mechanism, which considers the breakup

of N2 and O2 molecules [66]. This mechanism takes place due to the high

temperatures and pressures initiated by the lightning stroke. Lightning, which is

calculated internally in the model, contributes about 16% to the NOx global budget;

while fossil fuel is burning and biomass burning contributes close to 70% of the NOx

budget. Measured concentrations of NOx have substantial spatial and temporal

variability. This is due to the fact that the local chemical lifetime of NOx is less than

1 day in the polluted boundary layer and 5 to 10 days in the upper troposphere. The

effect of lightning on the NOx budget is important to NOx in the upper troposphere,

where the lifetime is longer. Many studies have looked at lightning produced NOx

[67].

1.20 Tropospheric Ozone is toxic to plants and human healths

Recent studies show that ozone is a big problem around the world which

affects vegetation and humans and contribute also to climate change. Tropospheric

ozone is the major ingredient in photochemical smog and, as mentioned earlier,

represents a considerable risk to vegetations and human beings. Effects of ozone may

occur at various levels of organization, i.e. from the cellular level through the level of

individual organs and plants to the level of plant communities and ecosystems [68].

Fig 1.6 shows climate change direct and indirect effects of ozone depletion.

Growth reduction from chronic exposures as well as crop yield losses,

reductions in annual biomass increments for forest trees and shifts in species

composition of semi-natural vegetation are other well-documented effects of ground-

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level ozone or surface ozone [69]. Current levels of ozone reduce yields of major

staple crops such as rice, wheat, corn, potato and soybean.

Fig1.6 Health impacts due to climatic changes and ozone layer depletion

1.21 Tropospheric ozone driver of climate change

Ground-level O3 increases also contribute to climate change through both

direct and indirect routes. Ozone concentrations should therefore be considered

alongside those of rising CO2 concentrations. The IPCC estimates that tropospheric

O3 increases since pre-industrial times have contributed somewhere between 0.25 and

0.65 W m–2 to global radiative forcing [70]. Increases in O3 will also have an indirect

effect on global warming by suppressing plant growth, reducing the land carbon sink

for CO2 and therefore increasing the rate at which CO2 increases in the atmosphere.

Experimental studies have shown that O3 reduces the additional carbon storage

arising from increased CO2 concentrations, but that elevated CO2 concentrations can

reduce the negative impacts of O3 on vegetation. A physiological model linking these

phenomena has recently demonstrated that the indirect radiative effects of O3 via

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reduced carbon sequestration could increase the total radiative forcing due to O3 over

the period 1900–2100 by at least 70% [71]. This suggests that tropospheric O3

increases are an even more important driver of global warming.

This suggest that future changes in climate may not have a major influence on

O3 concentrations globally, but that it is more important at the regional and local

scales. However, many of the climate processes which control O3 at these scales are

not yet captured well within global atmospheric chemistry models. This provides a

brief evaluation of which climatic processes may influence O3 concentrations in the

future. It also highlights the role of tropospheric O3 as a greenhouse gas. The

production of O3 is controlled by temperature, sunlight and humidity, and by the

long-range transport of pollutants all of which are sensitive to changes in climate.

1.22 Ozone effects on other things

There are further environmental effects of ozone, for example: Rubber, textile

dyes, fibers, and certain paints may be weakened or damaged by exposure to ozone.

Some elastic materials can become brittle and crack, while paints and fabric dyes may

fade more quickly. It also damages cotton, acetate, nylon, polyester, and other

textiles. Reactions involving ozone also cause deterioration of electronic devices.

1.23 Tropospheric ozone forcing future trend

1850-2000 forcing is mostly positive, except for the Antarctic. It peaks in the

northern subtropics. 2000-2100 tropospheric ozone forcing is large in the scenario

with large methane changes.

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1.24 Relation between stratospheric ozone and tropospheric ozone

One recent studies says that the nature of long term seasonal and yearly

variations of tropospheric and stratospheric ozone over thumba (8.5oN,77

oE) and

bangalore (13oN,77.5

oE) ,India. Seasonal variations clearly reveal that stratospheric

ozone concentration attained comparatively higher value in the months from july to

September while lower tropospheric ozone concentration at the same time over above

stations during period 1979-2005.Yearly variations shows increasing trend in

tropospheric ozone but decreasing trend in stratospheric ozone from 1979 to 2005.

Undesirable environmental effects due to such tropospheric rise and stratospheric

decline in ozone are also mentioned [72].

1.25 Total Ozone Column (TOC)

The most common ozone measurement unit is the Dobson Unit (DU). The

Dobson Unit is named after atmospheric ozone pioneer G.M.B. Dobson who carried

out the earliest studies on ozone in the atmosphere from the 1920s to the 1970s.

Fig 1.7 shows the TOC measured by Dobson unit. A DU measures the total amount

of ozone in an overhead column of the atmosphere.

Dobson Units are measured by how thick the layer of ozone would be if it

were compressed into one layer at 0 degrees Celsius and with a pressure of one

atmosphere above it. Every 0.01 millimeter thickness of the layer is equal to one

Dobson Unit.

The average amount of ozone in the stratosphere across the globe is about

300DU (or a thickness of only 3mm at 0oC and 1 atmospheric pressure!). Highest

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levels of ozone are usually found in the mid to high latitudes, in Canada and Siberia

(360DU).

Fig 1.7 Total Ozone column measured by Dobson Unit

1.26 Objectives of this study

1) To study and analyze the role of surface level ozone or ground level ozone and

total ozone column activity in the climate changes.

2) To measure the surface ozone at different sites over Tamil Nadu. Based on the

measured data forecasting future ozone value.

3) Before forecast, need to do Rescaled Analysis and Chaotic analysis of ozone

data.

4) Depends upon the ozone analysis we need to develop linear and non-linear

mathematical models for estimation of surface ozone and total column ozone.

5) To correlate total column ozone and rainfall of Kodaikanal using the classical

decomposition method and Auto Regressive Integrated Moving Average

method.

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6) To develop a Artificial Neural Network and Adaptive Neuro Fuzzy Inference

System (ANFIS) model for estimation of surface ozone as output and wind

speed, temperature, relative humidity as input.

1.27 Thesis outline

This Thesis consists of six chapters.

The First Chapter deals with introduction and explains the formation of

ozone, national ambient air quality standards of ozone, various ozone units, and

different levels of ozone measuring technique, effects of ozone on climate change,

effects of ozone on vegetation, effects of ozone on human health and environmental

problems. Future ozone trend, Total ozone column are discussed in this chapter.

The Second Chapter describes briefly the study area and the data used in the

study. Surface ozone along with different meteorological parameters such as

temperature, relative humidity, and wind speed are also measured and taken for the

study. In the study site area Chennai and Kodaikanal were considered. In Chennai site

diurnal and seasonal variations were observed. In Kodaikanal total column ozone

along with rainfall data were gathered and analyzed.

The Third Chapter is analysis of Hurst, Fractal dimension and chaotic nature

of ozone data .Hurst (H) and fractal dimension (D) determines whether the given time

series is completely random or has some long term memory. Chaotic analysis is used

to find the power of predictability. Whether the time series can be predicted for short

term or long term is identified by the chaotic analysis.

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The Fourth Chapter enlightens ozone forecasting. Based on the analysis of

ozone data various forecasting methods used. In this chapter SDPV Forecasting

Method is used. SDPV consists of Classical Decomposition (CD), Auto Regressive

Integrated Moving Average (ARIMA) methods in ozone Forecasting.

The Fifth Chapter elucidates DIMP Forecasting Method. DIMP consists of

Artificial Neural Network (ANN) and Adaptive Neuro Fuzzy Inference System

(ANFIS) Forecasting model. Chennai surface ozone data was analyzed by ANN and

ANFIS model.

The Sixth Chapter summarizes the significant findings of the research work.

Some essential conclusions are drawn in this chapter. The performance of four

forecasting methods is found. The recommendations for further research are given in

this chapter. The relevant references in connection with this work are given at the end

of each chapter. In addition the lists of publications are presented in the appendix

section.

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