Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB

First time observations of spectral aerosol optical depths (AODs) at Mohal (31.9°N, 77.11°E; altitude 1154 m amsl) in the Kullu valley, located in the northwestern Indian Himalayan region, have been carried out during Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), as a part of the Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP). AODs at six wavelengths are obtained using Microtops-II Sunphotometer and Ozonometer. The monthly mean values of AOD at 500 nm are found to be 0.27 ± 0.04 and 0.24 ± 0.02 during March and April, 2006 respectively. However, their monthly mean values are 0.33 ± 0.04 at 380 nm and 0.20 ± 0.03 nm at 870 nm during March 2006 and 0.31 ± 0.3 at 380 nm and 0.17 ± 0.2 at 870 nm during April 2006, showing a gradual decrease in AOD with wavelength. The Angstrom wavelength exponent 'α' had a mean value of 0.72 ± 0.05, implying reduced dominance of fine particles. Further, the afternoon AOD values are higher as compared to forenoon values by ~33.0% during March and by ~9.0% during April 2006 and are attributed to the pollutant lifted up from the valley by the evolving boundary layer. Besides the long-range transportation of aerosol particles by airmass from the Great Sahara and the Thar Desert regions to the observing site, the high values of AODs have also been influenced by biomass burning and frequent incidents of forest fire at local levels

Trace gases behaviour in sensitive areas of the northwestern Himalaya–A case study of Kullu-Manali tourist complex, India

197-203Surface concentration of the three important trace gases, ozone (O₃), nitrogen dioxide (NO₂) and sulphur dioxide (SO₂) were measured at three different tourist locations, namely Kullu, Manali and Kothi in the northwestern Himalayan region, which are located at 1220 m, 2050 m and 2530 m above the mean sea level mainly to asses the anthropogenic impact. The surface O₃ was monitored for four years during the period 1998 - 2002 and 2004 at the time of peak tourist season (May-June), and SO₂ and NO₂ were measured during the entire period in 2003. The peak O₃ concentrations reached close to 50 ppb level, while the annual mean concentrations of O₃, SO₂ and NO₂ remained within the United States Environmental Protection Agency’s (USEPA’s) National Ambient Air Quality Standards (NAAQS). The peak hourly average values of O₃ was 44 ppb at Manali and 32 ppb at Kothi during evening (1700 hrs IST), while that at Mohal (near Kullu) was 32 ppb in the afternoon (1500 hrs IST) period. The seasonally average value of maximum concentration of NO₂ was 3.8±0.6 μg m⁻³at Kothi and 7.6±1.0 μg m⁻³ at Mohal in autumn (October-November), while that of SO₂ was 21.4±1.8 μg m⁻³ at Kothi and 18.8±1.3 μg m⁻³ at Mohal during the monsoon (July-September) and summer (April-June) periods, respectively. Vehicular emissions and biomass burning for heating and cooking during the winter period (especially when power failure is common) as well as during forest fires could be the major contributors for increased emissions of these trace gases. However, the influence of long-range transport may also be important

Aerosols behaviour in sensitive areas of the northwestern Himalaya—A case of Kullu-Manali tourist complex, India

332-340Total suspended particulate (TSP) matter on fortnightly basis throughout the year and mass size distribution of aerosols as well as ultrafine aerosols on weekly basis in the months of May and June were monitored during 1996-2003 at different altitudinal locations of the Kullu-Manali tourist complex in the northwestern Himalaya. Concentration of TSP ranged from 35.8 (August 1996) to 207.3 μg m-3 (June 2003) at Mohal [1150 m from average sea level (ASL)] and from 31.7 (July 2003) to 239 μg m-3 (April 2001) at Manali (2050 m ASL). The mass size distribution of aerosols showed a bimodal distribution having one peak in the coarse size range (3.3-9 μm dia) and the other in the fine size range (0.08-2.1μm dia] at both the locations. Ultrafine aerosol (UA) (0.001-0.1 μ m radius) concentrations were found to be highest at the lowest experimental altitude site (Mohal) and vice versa. The diurnal variation of UA concentration for three years showed that the concentration ranges from 2640 (at 0500 hrs LT) to 5160 Number (N) cm-3 (at 1300 hrs LT) at Mohal and from 400 (at 0400 hrs LT) to 2190N cm-3 (at 1300 hrs LT) at Kothi. On an average, TSP crossed its permissible limit set by National Ambient Air Quality Standard (NAAQS) level in the sensitive areas such as Kullu-Manali hill spots. Bimodal nature mass size distribution indicates two important sources contributing in total aerosols-the fine mode, primarily due to anthropogenic activities and the coarse mode aerosols, mainly due to natural sources. Large number of concentration of ultrafine particles indicates the presence of air pollutants more low altitudes as compared to high altitudes

Chemical composition of size-separated aerosols at two rural locations in the Himalayan region

270-277Size-separated atmospheric aerosols were collected at Kothi (a hill top) and Mohal (a valley), situated at the foothills of western Himalayas during the summer season of 1999. Bimodal distribution of aerosols was observed at both the locations. However, at Kothi, fine size particles dominated (62%), whereas at Mohal, coarse size particles contributed more (75%). The SO4 and NO3 particles together contributed ~ 30% of the total measured chemical composition of aerosols. Burning of biomass and emissions from tourist vehicles could be the main local sources for these components. However, aerosols showed alkaline nature (Σ-Σ+ ratio< 1) due to the neutralizing effect of some cations such as Ca and NH4

Measurements of Particulate (PM2.5), BC and Trace Gases Over the Northwestern Himalayan Region of India

Ambient trace gases (NH3, NO, NO2 and SO2) and black carbon (BC) were measured along with particulate matter (PM2.5) over the northwestern Himalayan region (Palampur, Kullu, Shimla, Solan and Nahan) of Himachal Pradesh (HP), India in a campaign mode during 12-22 March 2013 to evaluate the ambient air quality of the region. The average mixing ratio of ambient NH3, NO, NO2 and SO2 were recorded as 7.1 +/- 2.6, 3.1 +/- 1.3, 3.9 +/- 1.4 and 1.7 +/- 0.7 ppb respectively over the northwestern Himalayan region. The average concentration of BC was estimated as 2.2 +/- 0.5 mu g m(-3) over the region whereas average concentration of PM2.5 mass was estimated as 41.8 +/- 7.9 mu g m(-3). The spatial variation of ambient trace gases (NH3, NO, NO2 and SO2), BC and PM2.5 over the northwestern Himalayan region, India reveals that the region is mainly influenced by local activities, i.e., tourism activities, agricultural activities, biomass burning and vehicular emission. A significant positive linear correlation of NH3 and NH4+ with SO42-, NO3- and Cl- (NH4+ vs. SO42-, r(2) = 0.652; NH4+ vs. NO3-, r(2) = 0.701; and NH4+ vs. Cl-, r(2) = 0.627) of the PM2.5 indicates the possible formation of (NH4)(2)SO4, NH4NO3 and NH4Cl aerosols over the region

Characteristics of spectral aerosol optical depths over India during ICARB

Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Ångström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Ångström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from tshe adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Ångström exponent (α) remained significantly lower (∼1) over the Arabian Sea compared to Bay of Bengal (BoB) (∼1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of α, showing dominance of accumulation mode aerosols, over BoB are associated well with the advection, above the boundary layer, of fine particles from the east Asian region during March and April. The change in the airmass to marine in May results in a rapid decrease in α over the BoB