Ground-level ozone is harmful to human health and the environment, especially on sunny days when its concentration can reach high levels. It is a precursor of photochemical smog, which has its fatal effects. Real-time O3 monitoring helps in calculating air quality index to deliver health advisories as well as formulating an action plan to meet standards. This article covers information on ozone, its sources, permissible levels in the ambient air, health and environmental impact, possible corrective measures, need for ozone monitors as well as different methods of ozone monitoring. What is Ozone? Ozone is a highly reactive gas with three oxygen atoms. It is a pale blue gas with a distinctively pungent, irritating smell resembling chlorine bleach, and can be detectable at 0.1 ppm concentrations in the air. Being a powerful oxidizing agent, it is highly combustible at 10 wt% or higher concentrations. Also, it is highly unstable and hence gets converted to O2 at high concentrations. Source: :http://www.chem.ucla.edu/~harding/IGOC/O/ozone.html Ozone in the Atmosphere Ozone occurs naturally through the reaction of solar ultraviolet (UV) radiation with molecular oxygen in the upper atmosphere (about 6 – 30 miles above the earth’s surface – Stratosphere). This “ozone layer” is called good ozone as it protects and shields the earth’s surface from harmful effects of the sun’s UV radiation. However, when it is formed just above the earth’s surface, even its low levels highly impacts human health and welfare making it “bad ozone”. Ground-level ozone is a secondary air pollutant formed primarily from the photochemical reactions of other air pollutants, specifically nitrogen oxides (NOx) and volatile organic compounds (VOCs). It is formed by the reaction of sunlight with air containing NOx and hydrocarbons directly at sources or at areas downwind of major sources of NOx and VOC where O3 or its precursors are carried by the winds.

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Ozone
All you need to know about...

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All you need to know about OzoneWHAT IS O3?
It is a highly reactive, pale blue gas with a
distinctively pungent, irritating smell resembling
chlorine bleach, and can be detectable at 0.1 ppm
concentrations in the air.
Being a powerful oxidizing agent, it is highly
combustible at 10 wt% or higher concentrations. It is
highly unstable and hence gets converted to O2 at
high concentrations.
Ground-level Ozone (O3) is a trace gas of the troposphere and a critical air pollutant with
three oxygen atoms.
Ground-level ozone has a atmospheric lifetime of about 22 days. It is removed from
the atmosphere either by deposition to the ground or on plants or in the formation of
smog.

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All you need to know about OzoneO3 in Atmosphere
Ozone is naturally present in the Stratosphere,
called “good ozone” as it protects and shields the
earth’s surface from harmful effects of the sun's
UV radiation.
However, when it is formed just above the earth’s
surface, it highly impacts human health and
welfare making it “bad ozone”.
Ground-level ozone is a secondary air pollutant
formed primarily from the photochemical
reactions of other air pollutants, specifically
nitrogen oxides (NOx) and volatile organic
compounds (VOCs).

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All you need to know about OzoneSOURCES
Significant sources of precursors of ozone include
Natural Sources: Forest fires and vegetation
Anthropogenic / Industrial Sources:
● On-road sources : cars, trucks, and buses, etc
● Off-road sources : aircraft, locomotives, etc.
● Non-road sources :construction, agricultural equipment, etc.
● Point sources : cement and power plants, other industrial
emissions
● Area sources : bakeries, paint shops, dry cleaners, etc.
● All other sources of NOx and VOC emissions

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All you need to know about Ozone
The breakpoints concentrations describing the quality of air based on the O3 concentrations
(μg/m3) for different countries are:
India (8-hr) US (8-hr) China (8-hr) EU (8-hr)
AQI Category
Break point
concentration
AQI Category
Break point
concentration
AQI Category
Break point
concentration
AQI Category
Break point
concentration
Good 50 Good 100 Excellent 116 Very low 60
Satisfactory 100 Moderate 160 Good 147 Low 120
Moderately
polluted
200
Unhealthy for
sensitive
215
Lightly
Polluted
186 Medium 180
Poor 265 Unhealthy 265
Moderately
Polluted
225 High 240
Very Poor 748 Very Unhealthy 800
Heavily
Polluted
733 Very high 240+
Severe 748+ Hazardous -
Severely
Polluted
-
Source: National Ambient Air Quality Index, CPCB (Oct 2014)
PERMISSIBLE LIMITS

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All you need to know about OzoneADVERSE IMPACTS
● Due to its high oxidizing potential, ozone reacts with a
wide range of cellular components causing damage to
mucous and respiratory tissues in humans, animals as
well as plants at levels.
● Ozone can irritate the eyes, nose, throat and the
respiratory system, causing coughing, and
uncomfortable sensation in the chest. It can aggravate
respiratory diseases such asthma and bronchitis.
● High level of ozone inhalation can cause heart diseases,
reduce lung capacity and continue to harm the lungs
even after symptoms disappear.
HEALTH IMPACTS OF O3

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All you need to know about OzoneADVERSE IMPACTS
ENVIRONMENTAL IMPACTS OF
O3
● Accumulation of ozone leads to formation
of smog which is a powerful eye irritant.
● Ozone affects the photosynthesis of trees and
plants and impairs their growth.

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All you need to know about OzoneCORRECTIVE MEASURES
The primary step is O3 monitoring to identify the areas with high O3 levels or areas where air
quality does not meet the O3 national standards. In addition to this following corrective
measures can be taken:
● Have a walk, use bicycles, public transport or carpool whenever possible.
● Refuel your vehicle after dusk and avoid overflowing your tank.
● Avoid keeping your vehicle idle for long.
● Promote the use of alternative fuels and improve quality fuels with high emission rates.
● Periodically maintain/service your vehicles to improve their performance and reduce
emissions.
● Avoid unnecessary use of paints or other products that release the solvent.
● Avoid any physical activity outside when pollution levels are high, especially on hot
days. Stay indoors until it cools down outside and the air is fresh.

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All you need to know about OzoneMONITORING METHODS
U.V. Photometry
The air sample taken by the ozone monitor is divided
into two parts and O3 is removed using a scrubber
from one part.
When O3 in the ambient air is exposed to ultraviolet
(UV) light at 254 nm wavelength, it absorbs the UV light
in proportion to its concentration present in the air.
This absorption is measured using a UV detector and
the ozone concentration is calculated as opposed to
the sample without ozone.

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All you need to know about OzoneMONITORING METHODS
Gas-Phase Chemiluminescence
When ambient air is mixed with ethylene, the ozone
present in the air reacts with ethylene, emitting light
proportional to the O3 concentration present in the air
sample. It is detected by a photomultiplier tube and
converted to O3 concentration values.
Semiconductor
When sensor is exposed to air sample, the O3 molecules
react on the metal oxide surface of the sensor and
dissociate into charged ions which alter the resistance of
the film which is measured and converted to the O3
concentration.

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All you need to know about OzoneMONITORING METHODS
Electrochemical
O3 monitors working on the
electrochemical principle are operated
based on diffusion of ozone into the sensor
which results in the production of an
electrical signal proportional to the O3
concentration.
It allows accurate measurement of even low
concentrations, which is essential in ozone
monitoring in the ambient conditions.

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All you need to know about OzoneOIZOM’S PRINCIPLE
Oizom’s POLLUDRONE measures more than 30
parameters including gaseous pollutants like CO,
SO2, O3, NO, NO2; dust particulates like PM2.5, PM10,
noise and weather parameters like rainfall, wind
speed and wind direction.
Most of the sensors measuring gases including
ozone work on the principle of electrochemical
sensing.
Real-time monitoring of O3 levels helps in
calculating air quality index to deliver health
advisories as well as formulating an action plan to
meet standards.