Naturally,
Ozone (O3) is a gaseous molecule having a bluish colour with fishy
smell. It is the natural constituent of the atmosphere with the pre-industrial
concentration of 10-15 ppb and present base line values of 30- 40ppb (Sitch et
al., 2007) over globe were recorded. O3 is a secondary air pollutant formed
from precursors such as NOx, NMVOCs, CH4 and CO in the presence of sunlight and
the process is called photochemical reaction. A brief description of the O3
formation in the atmosphere with the initial breakdown of nitrogen dioxide
(NO2) in the presence sunlight resulting  in nitric oxide and nascent oxygen formation.
O3 is formed from reaction between nascent oxygen and molecular oxygen is
summarized below as:

NO2
+ hv – NO + O

O
+ O2 – O3

Nitric
oxide (NO) react with O3 at low O3 concentration resulting in the formation of
NO2 and the process is called NO titration, is generally occur in urban areas (Mittal
et al., 2007). The presence of Volatile organic carbon (VOC) and free radicals,
consumes NO thus more O3 concentration in the atmosphere (especially rural
areas) has been recorded. At the same time, less diurnal variation was observed
in the rural areas because of low NOx concentrations (Mittal et al., 2007).

The
total O3 concentration in the atmosphere is contributed mainly by in-situ photochemical
reaction among O3 precursors (Sahu et al., 2016) and downward movement from
stratosphere (Lefohn et al., 2011). HTAP includes NA, EU, SA and EA in northern
mid-latitude conclude that in these region, the total atmosphere O3 contributes
by aprox. 25% from stratosphere, aprox. 25% originated from natural sources and
rest 50% released from anthropogenic activity. Out of 50% anthropogenic
addition, 20% generated in-situ by photochemical reaction while 25% are
transported through air masses from others polluted places. In the anthropogenic
addition, human activities play significant role in increasing surface O3
(TFHTAP, 2010). Ambient O3 concentrations contributed by anthropogenic
activities are variable, reducing in EU and NA but increasing in EA (Granier et al., 2011). At the same time, changes
reported from high to low latitudes NH (Parrish et al., 2013).   Ground level O3
concentration in East Asia has been increasing due to high precursor emission
contributed by human activities and more developing countries (Cooper et
al., 2014). Combustion of fossil fuel and biomass
burning are the major source of O3 precursor particularly in India ( Sinha et al., 2014).India reported
high O3 concentration in which highest O3 concentration typically high in
densely populated Indo-Gangaetic Plain of northern India. Exceptionally high O3
concentration was recorded in the China in june month with 30-60% high O3 and
3-4 times more CO compared to others sites (Zbinden et al. (2013).Human
plays major role in biomass burning which are roughly equal in both the
hemispheres (Dentener et
al., 2011). Biomass
burning global emission of NOx (main precursor of O3) from the fossil fuel and
biomass burning for the year 2005 was reported (Van der Werf et al., 2006). In
addition to this, transboundry movement of O3 precursors from the developing
countries contributes to increasing in background O3 concentration (Dentener et
al., 2006). . O3 concentration throughout the year is not uniform depending
upon the meteorology and precursors at a particular region, therefore,
troposphere O3 is a regional and global (hemisphere) scale pollution. O3 is a
greenhouse gas with the radiative force of 0.35 Wm-2 absorbing
radiation at 9.4 µm wavelength reflected from earth surface (Solomon et al.,
2007). O3 along with many others factors such as increasing temperature and
elevated CO2 results in climate change (Gilliland et al., 2015).