JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES, VOL. 118, 1513–1524, doi:10.1002/jgrd.50180, 2013
Transport effects on the vertical distribution of tropospheric ozone
over the tropical marine regions surrounding India
S. Lal,1 S. Venkataramani,1 S. Srivastava,1,4 S. Gupta,1,5 C. Mallik,1 M. Naja,2 T. Sarangi,2
Y. B. Acharya,1 and X. Liu3
Received 15 May 2012; revised 4 January 2013; accepted 10 January 2013; published 12 February 2013.
[1] The measurements of vertical distribution of ozone have been made over the Bay of
Bengal and the Arabian Sea in spring 2006 during a cruise campaign, namely, the Integrated
Campaign for Aerosol, Gases and Radiation Budget. The average tropospheric columnar
ozone (TCO) values are found to be 36.1 6.9 Dobson unit (DU) and 41.7 5.0 DU over the
Bay of Bengal and the Arabian Sea, respectively. In contrast to TCO, ozone mixing ratios are
higher by about 10 ppbv in the lower 3 km over the Bay of Bengal due to Indo Gangetic
outflow above the marine atmospheric boundary layer. Major contribution in the higher TCO
value over the Arabian Sea is, possibly, by stratospheric intrusion when ozone in the upper
troposphere is higher by about 20 ppbv. The lowest columnar ozone content of 22.4 DU was
observed on 30 March in the central Bay of Bengal due to convective activity resulting into
lower ozone throughout the troposphere, except between 6 and 10 km altitude. These near
simultaneous ozone observations over the Bay of Bengal and the Arabian Sea in spring season
have revealed the role of regional and long-range transport and local dynamics on the vertical
distribution of ozone over these tropical marine regions.
Citation: Lal, S., S. Venkataramani, S. Srivastava, S. Gupta, C. Mallik, M. Naja, T. Sarangi, Y. B. Acharya and X. Liu
(2013), Transport effects on the vertical distribution of tropospheric ozone over the tropical marine regions surrounding
India, J. Geophys. Res. Atmos., 118, 1513–1524, doi:10.1002/jgrd.50180.
1. Introduction
[2] Tropospheric ozone is a precursor of hydroxyl radicals
(OH), which determine the oxidation capacity of the troposphere [Jacob, 1999]. It is a potential greenhouse gas [e.g.
Gauss et al., 2003] and has deleterious effects on the human
health and plants at the elevated mixing ratios in the atmospheric boundary layer [e.g. Adams et al., 1989]. Study of
vertical distribution of ozone provides information on the
chemistry as well as on the dynamical factors affecting its
distribution. Tropospheric ozone has two main sources. In
the upper troposphere (from above about 10 km to the tropopause), it is mostly transported from the ozone rich stratosphere. While in the middle (approximately 3–10 km) and
lower troposphere (below about 3 km), it is formed by the
photo-oxidation of pollutants like CO, CH4, and nonmethane volatile organic compounds in the presence of
NOx and sunlight [Crutzen, 1995 and references there in].
Ozone in the troposphere has highly variable lifetime from
a few days in the moist tropical marine atmospheric
1
Physical Research Laboratory, Ahmedabad, India.
Aryabhatta Research Institute of Observational Sciences, Nainital, India.
3
Harvard-Smithsonian CFA, Cambridge, Massachusetts, USA.
4
Indian Institute of Remote Sensing, Dehradun, India.
5
KBS Certification Services Pvt. Ltd., Faridabad, India.
2
Corresponding author: S. Lal, Physical Research Laboratory, Navrangpura,
Ahmedabad-380009, India. (shyam@prl.res.in)
©2013. American Geophysical Union. All Rights Reserved.
2169-897X/13/10.1002/jgrd.50180
boundary layer (MABL) (from the ocean surface to about
2 km height) to months in the free troposphere (from the
top of the MABL up to the tropopause) [Fishman et al.,
1991]. Hence, it is used as a tracer for transport in the free
troposphere. The photochemical processes are rapid in the
tropical Asian region due to higher levels of OH radicals,
availability of intense solar radiation, and higher emissions
of anthropogenic pollutants. Higher levels of OH radicals
in the tropical region are due to higher levels of water vapor
and actinic flux. The marine regions in the lower troposphere
surrounding India get polluted from the transport of pollutants
including ozone as well as its precursors from the Indian
subcontinent [Lelieveld et al., 2001]. However, long-range
transport can affect ozone distribution in the free troposphere
[Cooper et al., 2010].
[3] The changes in ozone mixing ratios have important
implications toward radiative forcing and climate change
when they occur in the middle and upper troposphere
[Gauss et al., 2003]. The free tropospheric ozone distribution
is often affected by convective processes and stratospheretroposphere exchange. The intrusion of ozone-rich midlatitude
stratospheric air due to isentropic transport across the tropopause is an important phenomenon for the ozone enhancement
in the tropical upper troposphere [Stohl et al., 2003]. Another
important phenomenon that influences the tropospheric ozone
distribution is deep convection [Folkins et al., 2002; Kley
et al., 2007]. The tropical regions are characterized by strong
upwelling during most of the year. This transports boundary
layer pollutants into the free troposphere, from where horizontal winds can carry them to distant regions.
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