Vertical distribution of ozone in the lower troposphere over the Bay of Bengal and the Arabian Sea during ICARB-2006: Effects of continental outflow

Abstract

[1] Measurements of vertical distributions of ozone and meteorological parameters were made over the Bay of Bengal (BOB) and Arabian Sea (AS) from ocean research vessel Sagar Kanya during the period of 18 March to 10 May 2006 as a part of the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB). The observations showed a highly polluted layer (average ozone ∼68.0 ± 10.1 ppbv) over the northern BOB as compared to the northern AS (51.5 ± 7.6 ppbv), southern BOB (42.7 ± 12.8 ppbv), and southern AS (40.9 ± 9.5 ppbv) in the altitude range of 1-3 km. In this altitude range, specific humidity was lower by about 2-6 g/kg, and temperature was higher by 1°C-3°C over the northern BOB and northern AS as compared to their southern counterparts. This comparison and the total potential source contribution function analysis indicate that the observations over the northern BOB and the northern AS were influenced by the transport of continental air masses. The outflow from the polluted atmosphere over northern India, particularly over the Indo-Gangetic Plain, resulted in higher mixing ratios of ozone over the northern BOB. The air masses from the northern Indian region contributed an enhancement of about 13 ± 6 ppbv to the mixing ratio of ozone over the BOB in the altitude range of 0.75-3.0 km. The mixing ratios of ozone in the unperturbed marine air masses were found to be 11 ± 6 and 5 ± 2 ppbv lower than the average ozone over the BOB and AS, respectively. These results clearly show the outflow of continental air containing high ozone and possibly other pollutants over the northern BOB, which can have significant implications in the chemistry and climate of relatively cleaner regions.

Tropospheric ozone maxima observed over the Arabian Sea during the pre-monsoon

“…5). This theory was also proved by Srivastava et al (2011) from the TPSCF (total potential source contribution function) results. One explanation for the larger TOC over the AS in comparison to surrounded regions is the lower humidity which provides less favourable condition for ozone depletion by hydroxyl radicals (OH).…”

“…It is established in the previous studies that LRT plays an important role in the AS pre-monsoon ozone pool (Lal and Lawrence, 2001;Chand et al, 2003;Srivastava et al, 2011Srivastava et al, , 2012Lal et al, 2013Lal et al, , 2014. Trajectory models are used to investigate the LRT pathways of the air parcels.…”

“…In previous studies using the ozonesonde measurements above the west coast of India and the data from two campaigns 1999 INDian Ocean EXperiment (INDOEX) campaigns and the Integrated Campaign for Aerosols, Gases and Radiation Budget (ICARB) campaign, which was conducted during March-May 2006), the higher AS TOC during pre-monsoon season was confirmed to be significantly influenced by LRT of the continental anthropogenically influenced outflows from the Middle East, western India, Africa, North America and Europe (Lal and Lawrence, 2001;Chand et al, 2003;Srivastava et al, 2011Srivastava et al, , 2012Lal et al, 2013Lal et al, , 2014. In addition, by comparing the INDOEX ozone measurements from both sides (northern and southern) of the ITCZ (Intertropical Convergence Zone), the influence of the ITCZ functioning as a sink for ozone was determined by the observed 4 times higher TOC values on the northern side of AS compared to the southern side (Chand et al, 2003).…”

Transport effects on the vertical distribution of tropospheric ozone over the tropical marine regions surrounding India

“…This valuable data set provided an excellent opportunity to investigate the effects of transport, convective processes, and other physical and chemical effects on the vertical distribution of ozone over these marine regions. The ozone distributions in the lower part of the troposphere up to 4 km height over both the marine regions have been analyzed in detail and published in Srivastava et al [2011]. The present work is the extension of this work covering the entire troposphere including the 0-4 km height for the sake of completeness.…”

Variations in O<sub>3</sub>, CO, and CH<sub>4</sub> over the Bay of Bengal during the summer monsoon season: shipborne measurements and model simulations

“…Considering the aforementioned special characteristics of the BoB, as well as the considerable heterogeneity of trace gas and aerosol distribution, in situ measurements covering large areas are essential for investigating the distribution of pollutants and the controlling processes. Extensive in situ measurements of various trace gases over the BoB have been conducted in the following field campaigns: IN-DOEX during the winter months of 1998 and 1999 (Lelieveld et al, 2001;Mühle et al, 2002); the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB) during the March-May (pre-monsoon season) of 2006 Srivastava et al, 2011Srivastava et al, , 2012; the winter-ICARB (W-ICARB) during December-January 2009 Nair, 2010, 2014;; the Bay of Bengal Experiment (BOBEX)-I during February-March 2001 ; the Bay of Bengal Process Studies (BOBPS) during September-October 2002 ; BOBEX-II during February 2003 (Lal et al, 2007); and the other campaign conducted during October-November 2010 (Mallik et al, 2013).…”