title: Chemical characterization of rainwater at a high-altitude site "Nainital" in the central Himalayas, India.
abstract: The present study investigates the chemical composition of rainwater (RW) from a high-altitude site "Nainital" (1958 m above msl) in the central Himalaya region, to understand the influence of local, regional, and long-range transport of pollutants. A total of 55 (2 in pre-monsoon and 53 in monsoon) RW samples were collected during the study period (June-September 2012) and were analyzed for major anions and cations using an ion chromatograph. The pH of precipitation events ranged from 4.95 to 6.50 (average 5.6 ± 0.3) was observed during the monsoon period (near to the acidic), whereas during the pre-monsoon, the pH was 6.25 ± 0.49 (alkaline) over the study region; it is due the mixture of anthropogenic as well as the natural chemical constituents. The average ionic concentration (sum of measured chemical constituents) was ∼3 times higher during the pre-monsoon (986 ± 101 μeq/1) compared to that in the monsoon season (373 ± 37 μeq/1). This is mainly due to the presence of more natural aerosols in the pre-monsoon season which is also reflected in the pH of rainwater (average 6.25 ± 0.50) as well as ionic concentration. The chemical composition suggests that Ca2+was the major contributor (34%) among cations, followed by Na+(10%), K+(8%), and Mg2+(9%), whereas Cl-, NO3-, and SO42-contributed ∼13, 11, and 9%, respectively, among anions. The average ratio of acidic species (SO42-/NO3-) is 1.56, suggesting 61 and 39% contribution of SO42-and NO3-, respectively, which is very close to the estimated contribution of H2SO4(60-70%) and HNO3(30-40%) in the precipitation samples. Neutralization factors for Ca2+, Mg2+, and NH4+in RW at Nainital are 4.94, 1.21, and 0.37, respectively, indicating their crucial role in neutralization of acidic species. The non-sea-salt (NSS) contribution to total Ca2+, K+, and Mg2+is estimated to be ∼98, 97, and 74%, respectively, suggesting the dominance of crustal sources for cations. In contrast, the NSS contribution to the total Cl-and SO42-is 16 and 69% indicating their anthropogenic origin, respectively. Principle component analysis also suggests that the first factor (i.e., natural sources, mainly dust, and sea-salts) accounts for ∼33% variance, whereas the second factor (i.e., fossil fuel and biomass burning) accounts for ∼18% variance of the measured ionic composition. The remaining contributions are attributed to the mixed emission sources and transport of pollutants from Indo-Gangetic Plain (IGP) and western parts of India. The results of the present study reveal a significant contribution of crustal and anthropogenic sources in the RW and neutralization processes in the central Himalaya.
authors.affiliation: Indian Institute of Tropical Meteorology (Branch), Prof Ramnath Vij Marg, New Delhi, 110060, India. dsbisht@tropmet.res.in.
authors.forename: Deewan Singh
authors.initials: DS
authors.lastname: Bisht
authors.affiliation: Indian Institute of Tropical Meteorology (Branch), Prof Ramnath Vij Marg, New Delhi, 110060, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Srivastava
authors.affiliation: Aryabhatta Research Institute for Observational Science, Manora Peak, Nainital, India.
authors.forename: H
authors.initials: H
authors.lastname: Joshi
authors.affiliation: Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, India.
authors.forename: K
authors.initials: K
authors.lastname: Ram
authors.affiliation: Aryabhatta Research Institute for Observational Science, Manora Peak, Nainital, India.
authors.forename: N
authors.initials: N
authors.lastname: Singh
authors.affiliation: Aryabhatta Research Institute for Observational Science, Manora Peak, Nainital, India.
authors.forename: M
authors.initials: M
authors.lastname: Naja
authors.affiliation: Department of Geophysics, Banaras Hindu University, Varanasi, India.
authors.forename: M K
authors.initials: MK
authors.lastname: Srivastava
authors.affiliation: Indian Institute of Tropical Meteorology (Branch), Prof Ramnath Vij Marg, New Delhi, 110060, India.
authors.forename: S
authors.initials: S
authors.lastname: Tiwari
mesh_terms: D000531:Altitude; D004784:Environmental Monitoring; D007194:India; D011891:Rain / Q000737:chemistry*; D012621:Seasons
keywords: High altitude; Ionic concentration; Neutralizing factor; PCA; Rainwater chemistry