Effect of Dust and Anthropogenic Aerosols on Columnar Aerosol Optical Properties over Darjeeling (2200 m asl), Eastern Himalayas, India (original) (raw)
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Atmospheric Chemistry and Physics, 2011
We examine the distribution of aerosols and associated optical/radiative properties in the Gangetic-Himalayan region from simultaneous radiometric measurements over the Indo-Gangetic Plains (IGP) and the foothill/southern slopes of the Himalayas during the 2009 pre-monsoon season. Enhanced dust transport extending from the Southwest Asian arid regions into the IGP, results in seasonal mean (April-June) aerosol optical depths of over 0.6-highest over Southern Asia. The influence of dust loading is greater over the Western IGP as suggested by pronounced coarse mode peak in aerosol size distribution and spectral single scattering albedo (SSA). Transported dust in the IGP, driven by prevailing westerly airmass, is found to be more absorbing (SSA 550 nm <0.9) than the near-desert region in Northwestern (NW) India suggesting mixing with carbonaceous aerosols in the IGP. On the contrary, significantly reduced dust transport is observed over eastern IGP and foothill/elevated Himalayan slopes in Nepal where strongly absorbing haze is prevalent, as indicated by lower SSA (0.85-0.9 at 440-1020 nm), suggesting presence of more absorbing aerosols compared to IGP. Additionally, our observations show a distinct diurnal pattern of aerosols with charac
Atmospheric Research, 2014
Optical properties of aerosols over Hanle (4500 m amsl) in the western Himalayas were studied using skyradiometer observations during October 2007 to December 2010. Yearly mean value of aerosol optical depth (AOD) at 500 nm is 0.042 ± 0.002, which demonstrates the pristine environment of the station. Seasonal mean AODs at 500 nm during summer, autumn, winter, and spring are 0.044 ± 0.002, 0.031 ± 0.001, 0.031 ± 0.001, and 0.061 ± 0.002, respectively. The relatively high AOD during spring, associated with an elevated aerosol layer observed from space, supports the hypothesis of middle-upper tropospheric heating during pre-monsoon period. Seasonal mean values of Angstrom exponent (α) estimated from linear regression method varied from minimum 0.65 (spring) to maximum 1.02 (autumn). Dominance of coarse mode aerosols at the site is thus evident during spring. Analysis of AOD profiles obtained from satellite data and airmass back trajectories superimposed with fire-counts data indicated the presence of desertdust at the altitudes of 5 to 7 km amsl during the episodes of high AOD and low α. These trajectories indicated airmasses mostly coming from different desert regions, e.g in northwest Asia and Iran in the Middle east. Further, arrival of airmasses from the densely populated and industrialized Punjab and Haryana regions from the northwest of India apparently explains the relative contribution of transported anthropogenic aerosols over the station.
Meteorology and …, 2011
The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.98N, 77.128E) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500 nm, Å ngström exponent and turbidity coefficient are 0.24 ± 0.08, 1.02 ± 0.34 and 0.13 ± 0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550 nm over Mohal within the expected accuracy (Ds pk = ±0.05 ± 0.15s pk ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surfacereaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72 K day -1 , respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.
Journal of Geophysical Research, 2006
Collocated measurements of the mass concentrations of aerosol black carbon (BC) and composite aerosols near the surface were carried out along with spectral aerosol optical depths (AODs) from a high altitude station, Manora Peak in Central Himalayas, during a comprehensive aerosol field campaign in December 2004. Despite being a pristine location in the Shivalik Ranges of Central Himalayas, and having a monthly mean AOD (at 500 nm) of 0.059 0.033 (typical to this site), total suspended particulate (TSP) concentration was in the range 15 -40 g m -3 (mean value 27.1 8.3 g m -3 ). Interestingly, aerosol BC had a mean concentration of 1.36 0.99 g m -3 , contributed to ~5.0 1.3% to the composite aerosol mass.
Ground based measurement of aerosol optical depth (AOD) and black carbon (BC) aerosols were carried out over Dehradun during January to December 2007. The AOD values during winter (December-February) are low and found to be in the range of (0.08-0.38) than during summer (March-June) periods (0.32-0.62). The aerosol loading was observed to be high during summer period due to the long-range transportation of aerosol particles by air mass from the Thar Desert region to the observing site besides the biomass burning and frequent incidents of forest fire at local levels. The annual average BC concentration observed was found to be 4.3 + 0.62 µgm-3. Diurnal variation of BC shows a gradual build up in the morning hours between 0600 to 0900 local time and in evening from 1900 to 2200 hrs local time while low concentration is observed during day and night time. The analysis of traffic density measured in the city shows that it has direct influence on the BC concentration. BC concentration increases more than three times during morning and evening compared to afternoon and night hours. Seasonal variations of BC shows high concentration during winter dry season associated with the air masses predominantly coming from Indo-Gangetic plain rich in carbonaceous aerosols and minimum during monsoon season due to wash out. The BC concentration is found to have relationship with anthropogenic activities, boundary layer dynamics and biomass burning which has been observed by the MODIS fire data in and around the region. BC concentration were positive correlated with diurnal temperature range and negative correlated with rainfall and humidity. The values of aerosol optical depth and black carbon concentration over Dehradun have been compared with those reported from selected locations in India. INTRODUCTION Aerosols are important components of earth–atmosphere–ocean system. They affect climate through three primary mechanisms-direct radiative forcing (absorption and scattering of sun radiation), indirect radiative forcing (modifying the cloud properties thereby affecting albedo of clouds) and have indirect effect in the atmospheric chemistry by modifying the concentration of climate-influencing constituents (Schwartz et al., 1995) (such as GHG's). Aerosols enhances the back scattering of solar radiation and leading to negative radiative forcing while the absorbing black carbon (BC) aerosols leads to the positive effect. Black carbon aerosol, the optically absorbing part of the carbonaceous aerosols is the major anthropogenic component of atmospheric aerosol system. Black carbon is one of the important constituents of ambient particulate matter, which is emitted into the atmosphere as a by-product of combustion processes such as fossil fuels, vegetation burning, industrial effluents, motor vehicle and aircraft exhausts and are generally in the sub-micron region and considered as tracers of anthropogenic impact on environment. The increase in anthropogenic emission would increase in aerosol loading thereby reducing the incoming solar radiation reaching the ground surface. These effects influence regional aerosol radiative forcing (Haywood and Shine, 1997). It has been reported that one of the
Meteorology and Atmospheric Physics, 2011
The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.9ºN, 77.12ºE) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient are 0.24 ± 0.08, 1.02 ± 0.34 and 0.13 ± 0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550 nm over Mohal within the expected accuracy (Δ τ pλ = ±0.05 ± 0.15 τ pλ ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surface-reaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72 K day-1, respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.
2010
Intense anthropogenic emissions over the Indian sub-continent lead to the formation of layers of particulate pollution that can be transported to the high altitude regions of the Himalaya-Hindu-Kush (HKH). Aerosol particles contain a substantial fraction of strongly absorbing material, including black carbon (BC), organic compounds (OC), and dust all of which can contribute to atmospheric warming, in addition to greenhouse gases. Using a 3-year record of continuous measurements of aerosol optical properties, we present a time series of key climate relevant aerosol properties including the aerosol absorption (σ ap) and scattering (σ sp) coefficients as well as the single-scattering albedo (w 0). Results of this investigation show substantial seasonal variability of these properties, with long range transport during the pre-and post-monsoon seasons and efficient precipitation scavenging of aerosol particles during the monsoon season. The monthly averaged scattering coefficients range from 0.1 Mm −1 (monsoon) to 20 Mm −1 while the average absorption coefficients range from 0.5 Mm −1 to 3.5 Mm −1. Both have their maximum values during the premonsoon period (April) and reach a minimum during Monsoon (July-August). This leads to dry w 0 values from 0.86 (pre-monsoon) to 0.79 (monsoon) seasons. Significant diurnal variability due to valley wind circulation is also reported. Using aerosol optical depth (AOD) measurements,
Journal of Atmospheric …, 2012
a b s t r a c t The measurements of atmospheric aerosols, the major agents of climate forcing and respiratory problems carried out by Multi-wavelength Radiometer (MWR) at Mohal (31154 0 N, 77107 0 E, 1154 m amsl) in Kullu valley of the the Northwestern Himalayan region from April 2006 to March 2009 show that the values of the spectral aerosol optical depth (AOD) and turbidity parameter 'b' (an indicator of aerosol mass) are high in summer slightly less in monsoon, low in winter and lowest in autumn season, whereas theÅngström exponent 'a' (an indicator of relative abundance of fine to coarse particles) has an opposite trend. Average annual value of AOD at 500 nm is 0.24 7 0.01, 0.467 0.01 and 0.27 70.01 that of 'b' is 0.13 7 0.01, 0.22 7 0.02 and 0.167 0.01, while that of 'a' is 1.047 0.05, 1.16 7 0.05 and 0.81 70.06, respectively, for clear, hazy and partially clear sky days. The larger value of
Study of Aerosol Optical Properties Over Two Sites in the Foothills of the Central Himalayas
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Atmospheric aerosol possesses impacts on climate system and ecological environments, human health and agricultural productivity. The environment over Himalayas and Tibetan Plateau region are continuously degraded due to the transport of pollution from the foothills of the Himalayas; mostly the Indo-Gangetic Plain (IGP). Thus, analysis of aerosol optical properties over two sites; Lumbini and Kathmandu (the southern slope of central Himalayas) using AERONET’s CIMEL sun photometer were conducted in this study. Aerosol optical depth (AOD at 500 nm), angstrom exponent (α or AE), volume size distribution (VSD), single scattering albedo (SSA) and asymmetry parameter (AP) were studied for 2013–2014 and the average AOD was found to be: 0.64 ± 0.41 (Lumbini) and 0.45 ± 0.30 (Kathmandu). The average AE was found to be: 1.25 ± 0.24 and 1.26 ± 0.18 respectively for two sites. The relation between AO...