Size segregated mass concentration and size distribution of near surface aerosols over a tropical Indian semi-arid station, Anantapur: impact of long range transport

Regular measurements of size segregated as well as total mass concentration and size distribution of near surface composite aerosols, made using a ten-channel Quartz Crystal Microbalance (QCM) cascade impactor during the period of September 2007-May 2008 are used to study the aerosol characteristics in association with the synoptic meteorology. The total mass concentration varied from 59.70 ± 1.48 to 41.40 ± 1.72 μg m-3, out of which accumulation mode dominated by ~50%. On a synoptic scale, aerosol mass concentration in the accumulation (submicron) mode gradually increased from an average low value of ~26.92 ± 1.53 μg m-3 during the post monsoon season (September-November) to ~34.95 ± 1.32 μg m-3during winter (December-February) and reaching a peak value of ~43.56 ± 1.42 μg m-3 during the summer season (March-May). On the contrary, mass concentration of aerosols in the coarse (supermicron) mode increased from ~9.23 ± 1.25 μgm- 3during post monsoon season to reach a comparatively high value of ~25.89 ± 1.95 μg m-3 during dry winter months and a low value of ~8.07 ± 0.76 μg m-3 during the summer season. Effective radius, a parameter important in determining optical (scattering) properties of aerosol size distribution, varied between 0.104 ± 0.08 μm and 0.167 ± 0.06 μm with a mean value of 0.143 ± 0.01 μm. The fine mode is highly reduced during the post monsoon period and the large and coarse modes continue to remain high (replenished) so that their relative dominance increases. It can be seen that among the two parameters measured, correlation of total mass concentration with air temperature is positive (R2=0.82) compared with relative humidity (RH) (R2=0.75)

Temporal and spectral characteristics of aerosol optical depths in a semi-arid region of southern India

The spectral and temporal variations of aerosol optical depths (AOD) observed over Anantapur (a semi-arid region) located in the Southern part of India are investigated by analyzing the data obtained from a Multiwavelength Solar Radiometer (MWR) during January 2005-December 2006 (a total of 404 clear-sky observations) using the Langley technique. In this paper, we highlighted the studies on monthly, seasonal and spectral variations of aerosol optical depth and their implications. The results showed seasonal variation with higher values during pre-monsoon (March-May) and lower in the monsoon (June-November) season at all wavelengths. The pre-monsoon increase is found to be due to the high wind speed producing larger amounts of wind-driven dust particles. The post-monsoon (December-February) AOD values decrease more at higher wavelengths, indicating a general reduction in the number of bigger particles. Also during the post-monsoon, direction of winds in association with high or low pressure weather systems and the air brings more aerosol content to the region which is surrounded by a number of cement plants, lime kilns, slab polishing and brick making units. The quantity of AOD values in pre-monsoon is higher (low during post-monsoon) for wavelength, such as shortwave infrared (SWIR) or near infrared (NIR), which shows that coarse particles contribute more compare with the sub-micron particles. The composite aerosols near the surface follow suit with the share of the accumulation mode to the total mass concentration decreasing from ~70% to 30% from post-monsoon to pre-monsoon. Coarse mode particle loading observed to be high during pre-monsoon and accumulation mode particles observed to be high during post-monsoon. The backward trajectories at three representative altitudes with source point at the observing site indicate a possible transport from the outflow regions into Bay of Bengal, southern peninsular India and Arabian Sea. The temporal variations of AOD, Angstrom wavelength exponent and precipitable water content over Anantapur have also been compared with those reported from selected locations in India

A study on the variations of optical and physical properties of aerosols over a tropical semi-arid station during grassland fire

The present paper records the results of a case study on the impact of an extensive grassland fire on the physical and optical properties of aerosols at a semi-arid station in southern India for the first time from ground based measurements using a MICROTOPS-II sunphotometer, an aethalometer and a quartz crystal microbalance impactor (QCM). Observations revealed a substantial increase in aerosol optical depth (AOD) at all wavelengths during burning days compared to normal days. High AOD values observed at shorter wavelengths suggest the dominance of accumulation mode particle loading over the study area. Daily mean aerosol size spectra shows, most of the time, power-law distribution. To characterize AOD, the Angstrom parameters (i.e., α and β) were used. Wavelength exponent (1.38) and turbidity coefficient (0.21) are high during burning days compared to normal days, thereby suggesting an increase in accumulation mode particle loading. Aerosol size distribution suggested dominance of accumulation mode particle loading during burning days compared to normal days. A significant positive correlation was observed between AOD at 500 nm and water vapour and negative correlation between AOD at 500 nm and wind speed for burning and non-burning days. Diurnal variations of black carbon (BC) aerosol mass concentrations increased by a factor of ~2 in the morning and afternoon hours during burning period compared to normal days

Characterization of aerosol black carbon over a tropical semi-arid region of Anantapur, India

Black carbon (BC) aerosol mass concentrations measured using an aethalometer at Anantapur, a semi-arid tropical station in the southern part of peninsular India, from August 2006 to July 2007 are analyzed. Seasonal and diurnal variations of BC in relation to changes in the regional meteorological conditions have been studied along with the mass fraction of BC to the total aerosol mass concentration (M-t) and fine particle mass (FPM) concentration in different months. The data collected during the study period shows that the annual average BC mass concentration at Anantapur is 1.97 +/- 0.12 mu g m(-3). Seasonal variations of BC aerosol mass concentration showed high during the dry (winter and summer) seasons and low during the post-monsoon followed by the monsoon seasons. Diurnal variations of BC aerosols attain a gradual build up in BC concentration from morning and a sharp peak occurs between 07:00 and 09:00 h almost an hour after local sunrise and a broad nocturnal peak from 19:00 to 21:00 h with a minimum in noon hours. The ratio of BC to the fine particle mass concentration was high during the dry season and low during the monsoon season. The regression analysis between BC mass concentration and wind speed indicates that, with increase in wind speeds the BC mass concentrations would decrease and vice-versa. Aerosol BC mass concentration shows a significant positive correlation with total mass concentration (M-t) and aerosol optical depth (ACID, tau(p)) at 500 nm. (C) 2010 Elsevier B.V. All rights reserved

Simultaneous Measurements of Surface Ozone at Two Sites over the Southern Asia: A Comparative Study

This article presents variations of simultaneous measurements of near surface ozone (O(3)) at two sites namely Anantapur [14.62 degrees N, 77.65 degrees E], a semi arid rural location in India and Xi&#39;An [34.20 degrees N, 108.98 degrees E], a semi arid urban location in China during January-July 2009. The results showed a clear diurnal cycle of O(3) with a minimum at sunrise and a maximum at noon for both the sites. The monthly average diurnal variation shows that the maximum/minimum ozone was observed in March/July whereas in Xi&#39;An maximum/minimum ozone was observed in July/February because of different climatic zones and rainfall activity. The average diurnal variation of O(3) for different seasons (summer and winter) shows higher ozone concentration at Anantapur than at Xi&#39;An. This may be due to slower titration of NO in the evening hours at Anantapur. But in Xi&#39;An, the highest ozone levels recorded in noon hours for some days in June and July months. This is mainly due to strong emissions of NO(x), VOC and high solar radiation and this implies significant negative effects on vegetation and regional air quality around Xi&#39;An. The rate of increase of ozone is almost the same at two sites but the rate of decrease of ozone is more at Xi&#39;An than at Anantapur which is due to the higher NO(x) concentration from vehicular emission and also due to the fast titration of O(3). The maximum 54% of frequency distribution of ozone lies between 20-45 ppbv at Anantapur whereas in Xi&#39;An 34% lies in the range of 0-5 ppbv, 32% of Ozone lie between 5-20 ppbv and 24% of all O(3) lie in the range of 20-45 ppbv.</p

Observational studies on the variations in surface ozone concentration at Anantapur in southern India

Continuous measurements of surface ozone (O3) at a semi-arid rural site (14.62&#176;N, 77.65&#176;E) in Anantapur, India during the period from December 2008 to July 2009 are presented. The diurnal variation in O3 shows high concentrations (in the range of 25-77 ppbv) during daytime and low concentrations during late evening and early morning hours, due to slower titration of ozone by oxides of nitrogen (NOx). The monthly average high (low) O3 is 56.09 &#177; 10.1 ppbv (27.45 &#177; 2.3 ppbv) at noon in March (July), due to a possible increase in precursor gas concentration by anthropogenic activity and also due to the influence of local meteorological conditions. Furthermore, O3 concentration has been observed as a function of season, which shows that the highest O3 concentration is 52.05 &#177; 10.2 ppbv in the summer and the lowest 30.96 &#177; 5.7 ppbv in the monsoon season. The rate of the increase of surface ozone is high (2.11 ppbv/h) in March and low (0.32 ppbv/h) in July. Among the meteorological parameters, daily average ozone shows a significantly positive correlation with temperature (R = 0.76) and negative correlation with relative humidity (R = - 0.62). Throughout the study period, high ozone concentrations were mainly associated with the winds from 150.5&#176; to 260.1&#176;. The weekend ozone effect indicates that higher O3 concentration on weekend compared to weekday suggests that the photochemical production of O3 is non-linear over this site. The results also show that high aerosol concentration has very strong impact on photochemical activities and ozone formation. The correlation between ozone and aerosol concentrations appears in a non-linear feature. Backward trajectory analysis shows that the increase of ozone concentration and the relatively constant high ozone concentrations during the summer might originate from the transport of ozone rich airmass above the boundary layer especially in Northern India and East Asian regions. On the other hand, the airmasses coming from the south over the Indian Ocean contributes low amount of ozone during the monsoon

Characterization of aerosol black carbon over a tropical semi-arid region of Anantapur, India

Black carbon (BC) aerosol mass concentrations measured using an aethalometer at Anantapur, a semi-arid tropical station in the southern part of peninsular India, from August 2006 to July 2007 are analyzed. Seasonal and diurnal variations of BC in relation to changes in the regional meteorological conditions have been studied along with the mass fraction of BC to the total aerosol mass concentration (Mt) and fine particle mass (FPM) concentration in different months. The data collected during the study period shows that the annual average BC mass concentration at Anantapur is 1.97 ± 0.12 μg m−3. Seasonal variations of BC aerosol mass concentration showed high during the dry (winter and summer) seasons and low during the post-monsoon followed by the monsoon seasons. Diurnal variations of BC aerosols attain a gradual build up in BC concentration from morning and a sharp peak occurs between 07:00 and 09:00 h almost an hour after local sunrise and a broad nocturnal peak from 19:00 to 21:00 h with a minimum in noon hours. The ratio of BC to the fine particle mass concentration was high during the dry season and low during the monsoon season. The regression analysis between BC mass concentration and wind speed indicates that, with increase in wind speeds the BC mass concentrations would decrease and vice-versa. Aerosol BC mass concentration shows a significant positive correlation with total mass concentration (Mt) and aerosol optical depth (AOD, τp) at 500 nm

Characterization of PM, PM₁₀ and PM_2.5 mass concentrations at a tropical semi-arid station in Anantapur, India

95-104The particulate matter (PM), PM10 and PM2.5 concentrations are estimated from regular measurements of size segregated as well as total mass concentration of near surface composite aerosols, using a ten-channel Quartz Crystal Microbalance (QCM) Cascade Impactor in a tropical semi-arid station, Anantapur, India for the period May 2006 – April 2007. The monthly variations of PM, PM10 and PM2.5 and season-wise shares of PM10 and PM2.5 to PM have been computed. The highest contribution of PM10 to PM has been noticed during local summer season, while the maximum share of PM2.5 to PM has been noticed during the winter season. The average values of PM, PM10 and PM2.5 mass concentrations have been found to be 21.21±1.21, 18.7±1.06 and 17.02±1.28 g m-3, respectively. Seasonally, the concentration has been highest in winter (24.62±3.53, 22.07±2.56, 21.29±2.31) and lowest in monsoon (18.12±1.62, 16.46±1.82, 14.47±1.57) for PM, PM10 and PM2.5, respectively. The back trajectory cluster analysis revealed that the aerosol loading has been significantly higher in fine mode during periods of continental air mass (winter) but when the winds shift to marine (monsoon), the loading became higher due to major contribution of sea salt aerosols, particularly in the coarse mode. PM10 and PM2.5 concentrations has been highly correlated with PM and inversely correlated with local wind speed. The results of this analysis underlined the importance of local emission sources, mostly from anthropogenic, which are responsible for the high PM10 and PM2.5 concentration levels observed during this one year - sampling period

Potential source regions contributing to seasonal variations of black carbon aerosols over Anantapur in Southeast India

Continuous measurements of black carbon (BC) mass concentration performed at Anantapur [14.62°N, 77.65°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 µg/m³ 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 ~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 μg/m³ in the winter, 3.77 ± 1.23, 1.55 ± 0.51, and 2.33 ± 0.82 µg/m³ in the summer, monsoon and postmonsoon seasons, respectively. High BC values tend to occur when the wind is directed from the 180–225° 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 Ångström exponent (alpha)