Himalayan snow chemistry: Chemical composition of fresh snow samples from Kashmir valley

The present paper deals with variability in snow chemistry of various sites spread in six districts of the Kashmir Himalayan valley, experiencing frequent snow fall during winter ( Dec.- Feb). Chemical composition of fresh snow samples shows wide changes in pH (5.8–7.3), dissolved oxygen content (22-26 mg L -1 ), and total alkalinity (2-3 mg L -1 ). The levels ( mg L -1 ) of calcium (13.3– 28 ), magnesium (8-12 ), chloride (15-30), sulphate (2-8), silicate (1-4) and nitrate (1.9-3.9) differed considerably. The study makes a strong plea for in-depth investigations of snow chemistry of littleexplored Himalayan region, useful for assessing the impact of environmental pollution.

Pradesh, Haryana and the hills of western Uttar Pradesh and Uttranchal.The snowfall recorded at Agrometerological Observatory Shalimar (SKUAST-K) Kashmir during the winter of December, 2004 and Feb. 2005 is given in Table 1.

Sampling procedure and Analytical Methods
The fresh snow samples were collected from various sampling sites on the dates shown in Table 2.The snow samples were collected with a glass cylinder 40 cm long and 5 cm diameter.

RESULTS AND DISCUSSION
The average concentration of pH and dissolved oxygen content, and major ionic forms of the snow samples collected from different sites of Kashmir valley are given in Table 3.The data indicate that the pH of the snow samples was the lowest (5.84) in HMT area of Srinagar city ,and for other sites pH values ranged from 6.2 (Anantnag) to 7.31 (Shalimar).The reference level commonly used to compare acid precipitation to natural precipitation is pH 5.6, the pH that results from the equilibration of CO 2 with precipitation.This reference level has been chosen because of the ubiquity of CO 2 in the global atmosphere and because of the absence of data on other acids or basics (Naik et al 1995).However, Galloway et al (1982) believe that there is no single natural pH of precipitation applicable to the whole globe, but rather several natural values, each unique to a region, the size of a continent or an ocean.The lowest values for pH in the snow samples of the HMT area could be attributed to the presence of higher concentration of species like NO 3 and SO 4 in the atmosphere of this region due to the operation of small-scale Each sample was melted in the plastic tub covered with a glass sheet pre-cleaned with deionized water and allowed to reach ambient room temperature.After melting, the snow water was transferred into a 1 liter capacity polythene bottles which was sealed and returned to the laboratory for analysis.
The pH of the snow-melt was measured immediately by using electronic digital pH meter (Systronics 327).Methods recommended by Mackereth (1963) and the American Public Health Association (1992) were used for various physical and chemical variables.The Cl content was determined tritrimatrically against AgNO 3 and total alkalinity was estimated against standard solution of H 2 SO .Dissolved oxygen (DO) was determined by Winkler's reagent and titrated against standard solution of Na 2 S 2 0 3 ,.Nitrate-nitrogen was estimated spectrophotometrically following phenol-disulphonic The chloride content and total alkalinity in the snow samples ranged from 15-28 and 2.-3 mg L -1 respectively in different zones of Kashmir valley and suggest a strong influence of alkaline dust particles which might have originated from Indian plains and arid zones in the west and have been transported to the region by south westerly, winds (Naik et al 1995).The data also indicate that dissolved oxygen content in the snow samples collected from different sites of Kashmir valley ranged from 22-24 mg L -1 and suggests a fairly good concentration of O 2 in the atmosphere.
High concentration of NO 3 (3.9mg L -1 ) and SO 4 (8 mg L -1 ) were recorded in the HMT area compared to other sites.Since SO 2 and NO 2 are mainly derived from anthropogenic sources, the high levels of these species in the snow samples of HMT area are likely to be due to industrial activity in the area.The other sites (e.g.Lal Chowk ) has significantly higher traffic-flow with appreciably higher NO x concentration in the atmosphere.However, during night time, the traffic usually remains off the road and consequently snow recorded lesser concentration of these species as the snowfall was recorded during the night hours.Under natural conditions, nitrate particles of submicron size in the atmosphere may be formed by gas to particle conversion process (Cox, 1974).Under normal atmospheric conditions, HNO 3 can initially form Aitken nuclei which will grow rapidly into a submicron sizes and react with NH 4 to NH 4 NO 3 .This reaction is reversible and temperature dependent (Wolff, 1984).The formation of NH 4 NO 3 in tropical countries is rare due to persistence of higher temperature.However, HNO 3 can react with soil derived or some industrial particulates and become incorporated in snow as the coarse aerosol mode (Wolff, 1984).It is also clear from the data that the other sites( viz.Shalimar, Rafiabad, Tral, Magam and Anantnag) have almost negligible traffic-flow and consequently low concentrations of the NO 3 and SO 4 were observed during the present study.
The data also reveal that HMT site recorded low content of Ca 2 (12 mg L -1 )and Mg (8 mg L -1 ) .However, highest values were observed in Lal Chowk area ( Ca=28.05 and Mg= 16.5 mg L -1 ) .For other sites (Table 3), the values differed markedly; Anantnag ( Ca=13 mg L -1 ) and Shalimar/ Tral (Ca=20 mg L-1).The Magnesium content fluctuated narrowly between 10-12 mg L-1 for the sites.The influence of alkaline components on the pH of the rain, cloud and fog water in India has been reported earlier (Khemani et al 1987 ).The higher concentration of alkaline components (Ca and Mg) are responsible for the higher pH of precipitation in India and the alkaline pH in the snow samples collected from Lal Chowk, Shalimar, Rafiabad, Dragmulla, Tral, Magam and Anantnag is consistent with these observations.The presence of appreciably higher concentration of Ca has also been reported in the snow samples of Mt.Everest by Marinoni et al (2001).Other related studies have also shown higher ionic concentration of Ca in the premonsoon snow and have opined that it may be as a result of  (Parrington et al, 1983).On the other hand, relatively low concentration of Ca and Mg in the snow samples collected from HMT area may also be one of the factors responsible for its low pH value.

Conclusion
Analytical research on ionic composition of fresh snow is a useful tool for assessing the environmental impact of air pollution sources as well as the transport and deposition of various air pollutants.The study has indicated the presence of highly appreciable concentration of anions (Cl) total alkalinity, MgSO 4 and SiO 3 as well as cations (Ca and Mg) in the fresh snow samples collected from different areas of Kashmir valley.,The presence of these ions seems directly related to site-specific environmental conditions of the Himalayan region.

Table - 1: Snowfall recorded at Agro-meteorological Observatory SKUAST-K, Shalimar
Source: Division of Agronomy, SKUAST-K, Shalimar acid method, while sulphate was determined by the turbidimetric method.Silicate content was also determined colorimetrically by using acidmolybdate solution.Analysis of cations (Ca and Mg) was done titrametrically using Na 2 EDTA (disodium dihydrogen ethylene diaminetetraacetate).