Browsing by Author "Gopal, K. Rama"

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Analysis of Diurnal and Seasonal Behavior of Surface Ozone and Its Precursors (NOx) at a Semi-Arid Rural Site in Southern India
(2012-12-01)
Reddy, B. Suresh Kumar
;
Kumar, K. Raghavendra
;
Balakrishnaiah, G.
;
Gopal, K. Rama
;
Reddy, R. R.
Surface measurements of O-3, NO, NO2 and NOx have been made over a semi-arid rural site, Anantapur (14.62 degrees N; 77.65 degrees E; 331 m asl) in southern India, during January-December 2010. The highest monthly mean O-3 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 O-3, NO and NO2 indicate that the level of oxidant concentration ([OX] = NO2 + O-3) at a given location is the sum of NOx-independent "regional contribution" (background level of O-3) and linearly NOx-dependent "local contribution". The O-3 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 [O-3] suggests that every 1 mu g/m(3) increase in black carbon aerosol mass concentration causes a reduction of 4.7 mu g/m(3) 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.
Potential Source Regions Contributing to Seasonal Variations of Black Carbon Aerosols over Anantapur in Southeast India
(2012-06-01)
Reddy, B. Suresh Kumar
;
Kumar, K. Raghavendra
;
Balakrishnaiah, G.
;
Gopal, K. Rama
;
Reddy, R. R.
Continuous measurements of black carbon (BC) mass concentration performed at Anantapur [14.62 degrees N, 77.65 degrees E, 331 m asl], a suburban location in southeast India, using an Aethalometer from January to December, 2010, are analyzed and discussed here. The annual mean BC mass concentration ([BC]) was 3.03 +/- 0.27 mu g/m(3) for the above study period. The sharp morning (fumigation) peak occurs between 07:00 and 08:00 h almost an hour after the local sunrise while a broad evening (nocturnal) peak is at similar to 21:00 h with a minimum in noon hours (14:00-16:00 h). The seasonal mean values of [BC] are 5.05 +/- 0.51 mu g/m(3) in the winter, 3.77 +/- 1.23, 1.55 +/- 0.51, and 2.33 +/- 0.82 mu g/m(3) in the summer, monsoon and postmonsoon seasons, respectively. High BC values tend to occur when the wind is directed from the 180-225 degrees sector, which may be well defined by the geographical location of the observation site. During the winter, the trajectory air mass pathways originated through north or central India with significant advection of continental aerosols arriving before the measurement region, results in an enhanced [BC]. Whereas in the monsoon season, the pristine marine air mass from the oceanic environment led to decrease in the concentration of BC. Comparison of monthly mean variations in AOD at 500 nm and black carbon aerosols is observed to be positive with poor correlation coefficient of 0.42. The ratio of BC/PM2.5 varied from 1.3% to 7.2% with a mean value of 4.6% at Anantapur during the observation period and this ratio decreased with decreasing Angstrom exponent (alpha).