Abstract
Surface measurements of O3, NO, NO2 and NOx have been made over a semi-arid rural site, Anantapur (14.62°N; 77.65°E; 331 m asl) in southern India, during January-December 2010. The highest monthly mean O3 concentration was observed in April (56.1 ± 9.9 ppbv) and the lowest in August (28.5 ± 7.4), with an annual mean of 40.7 ± 8.7 ppbv for the observation period. Seasonal variations in O3 concentrations were the highest during the summer (70.2 ± 6.9 ppbv), and lowest during the monsoon season (20.0 ± 4.7 ppbv), with an annual mean of 40.7 ± 8.7 ppbv. In contrast, higher NOx values appeared in the winter (12.8 ± 0.8 ppbv) followed by the summer season (10.9 ± 0.7 ppbv), while lower values appeared in the monsoon season (3.7 ± 0.5 ppbv). The results for O3, NO and NO2 indicate that the level of oxidant concentration ([OX] = NO2 + O3) at a given location is the sum of NOx-independent “regional contribution” (background level of O3) and linearly NOx-dependent “local contribution”. The O3 concentration shows a significant positive correlation with temperature, and a negative correlation with both wind speed and relative humidity. In contrast, NOx have a significant positive correlation with humidity and wind speed, and negative correlation with temperature. The slope between [BC] and [O3] suggests that every 1 μg/m3 increase in black carbon aerosol mass concentration causes a reduction of 4.7 μg/m3 in the surface ozone concentration. A comparative study using satellite data shows that annual mean values of tropospheric ozone contributes 12% of total ozone, while near surface ozone contributes 82% of tropospheric ozone. The monthly mean variation of tropospheric ozone is similar to that tropospheric NO2, with a correlation coefficient of +0.80.
Highlights
Industrialization, urbanization, rapid traffic growth and increasing levels of anthropogenic emissions have resulted in a substantial deterioration of air quality over Asia (Levy et al, 1999; Streets and Waldhoff 1999; Yienger et al, 2000)
The concentrations of Nitrogen monoxide (NO) and O3 were higher during day time while opposite trends exist for NO2 and nitrogen oxide (NOx)
This is mainly attributed to the photochemical reactions of NOx and O3 and the balance between the emissions and mixing processes of both horizontal and vertical convections
Summary
Industrialization, urbanization, rapid traffic growth and increasing levels of anthropogenic emissions have resulted in a substantial deterioration of air quality over Asia (Levy et al, 1999; Streets and Waldhoff 1999; Yienger et al, 2000). Tropospheric ozone is one of the important greenhouse gases and contributes to global warming and climate change (IPCC, 2007; Kulkarni et al, 2011). Tropospheric ozone is an important air pollutant threatening human health and vegetation growth (Lippmann, 2009). It is one of the key species affecting the chemical properties of the atmosphere (Sitch et al, 2007). Variations in ozone concentration are controlled by a number of processes
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