Browsing by Author "Sivakumar, V."

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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.
Ground-based in situ measurements of near-surface aerosol mass concentration over Anantapur: Heterogeneity in source impacts
(2013-01-01)
Reddy, B. S. K.
;
Kumar, K. R.
;
Balakrishnaiah, G.
;
Gopal, K. R.
;
Reddy, R. R.
Surface measurements of aerosol physical properties were made at Anantapur (14.62A degrees N, 77.65A degrees E, 331 m a.s.l), a semiarid rural site in India, during August 2008-July 2009. Measurements included the segregated sizes of aerosolsas as well as total mass concentration and size distributions of aerosols measured at low relative humidity (RH < 75%) using a Quartz Crystal Microbalance (QCM) in the 25-0.05 mu m aerodynamic diameter range. The hourly average total surface aerosol mass concentration in a day varied from 15 to 70 mu g m(-3), with a mean value of 34.02 +/- 9.05 mu g m(-3) for the entire study period. A clear diurnal pattern appeared in coarse, accumulation and nucleation-mode particle concentrations, with two local maxima occurring in early morning and late evening hours. The concentration of coarse-mode particles was high during the summer season, with a maximum concentration of 11.81 +/- 0.98 mu g m(-3) in the month of April, whereas accumulationmode concentration was observed to be high in the winter period contributed > 68% to the total aerosol mass concentration. Accumulation aerosol mass fraction, A (f) (= M (a)/M (t)) was highest during winter (mean value of A (f) 0.80) and lowest (A (f) 0.64) during the monsoon season. The regression analysis shows that both R (eff) and R (m) are dependent on coarse-mode aerosols. The relationship between the simultaneous measurements of daily mean aerosol optical depth at 500 nm (AOD(500)) and PM2.5 mass concentration ([PM2.5]) shows that surface-level aerosol mass concentration increases with the increase in columnar aerosol optical depth over the observation period.