Spatial Heterogeneity in Tropospheric Column Ozone over the Indian Subcontinent: Long-Term Climatology and Possible Association with Natural and Anthropogenic Activities

Gayatry Kalita,Pradip Kumar Bhuyan

doi:10.1155/2011/924516

Abstract

Monthly averaged tropospheric ozone residual (TOR) data from TOMS and OMI during the period 1979–2009 are used to study the spatial distribution of tropospheric column ozone within the landmass of the Indian subcontinent, the Tibetan plateau in the north and the Bay of Bengal in the south. The climatological mean shows seasonal maxima in spring and minima in winter in all the regions. The oceanic regions exhibit broad summer maximum and the maximum to minimum ratio is the lowest for these regions. The concentration of tropospheric column ozone is found to be highest in North Eastern India (NE) and the Indo Gangetic plains (IGP). NE ozone concentration exceeds that of IGP during spring whereas in post monsoon and winter reverse is the case. In the monsoon season, O3levels in the two regions are equal. The spring time highest level of tropospheric column ozone over NE region is found to be associated with highest incidence of lightning and biomass burning activity. The Stratosphere-Troposphere exchange is also found to contribute to the enhanced level of ozone in spring in NE India. A net decrease in tropospheric ozone concentration over NE during the period 1979 to 2009 has been observed.

Highlights

Tropospheric ozone is a secondary pollutant which is not emitted directly into the atmosphere but is formed in situ from complex mixture of precursor pollutants such as carbon monoxides, volatile organic compounds, and nitrogen oxides (CO, VOC, and NOx)
Trop O3 is lowest in Tibetan Himalayas from October to March, while it is lowest in Southern India (SI) and South Bay of Bengal (SBoB) from April to September
This is possibly due to the fact that SI and SBoB are around the equator, and production and loss mechanism are likely to be influenced by the ocean, where precursors are less for ozone production

Summary

Introduction

Tropospheric ozone is a secondary pollutant which is not emitted directly into the atmosphere but is formed in situ from complex mixture of precursor pollutants such as carbon monoxides, volatile organic compounds, and nitrogen oxides (CO, VOC, and NOx). The ground-based measurements of tropospheric ozone give limited data in time and space, whereas airborne or satellite observations of tropospheric ozone from space offer the opportunity to measure the distribution over large areas, and to study large-scale temporal and spatial behaviour [1, 2] This is of great importance since ozone formed over source regions, where large amounts of ozone precursors are emitted, can be transported over great distances and affect areas far from the source. In the Indian tropical region, with increasing emissions of O3 precursors such as oxides of nitrogen (NOx), volatile organic compounds (VOCs) [19], carbon monoxide (CO) [20], and nonmethane hydrocarbons (NMHCs) [21] from traffic, industry and large-scale biomass burning, the potential of tropospheric O3 production is enhanced [22,23,24,25,26]. The long-term trend in tropospheric column ozone over NE India has been studied

The Study Area

Results

Conclusions