Pranamika Bhuyan1,2, Md. Sahbaz Ahmed1, Philip K. Hopke  3,4, Raza R. Hoque  1,3

1 Department of Environmental Science, Tezpur University, Tezpur 784028, India
2 Department of Environmental Studies, Assam Women’s University, Jorhat 785004, India
3 Department of Public Health Sciences, University of Rochester Medical Center, Rochester, NY 14642, USA
4 Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY 13699, USA


Received: March 17, 2020
Revised: September 7, 2020
Accepted: September 10, 2020

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

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Bhuyan, P., Ahmed, M.S., Hopke, P.K. and Hoque, R.R. (2020). Understanding the Chemistry and Sources of Precipitation Ions in the mid-Brahmaputra Valley of Northeastern India. Aerosol Air Qual. Res. 20: 2690–2704.


  • Chemistry of rainwater for 3 years over mid-Brahmaputra region of NE India assessed.
  • Most rain events were alkaline, chemistry depicts seasonality, long-range influence.
  • Local crustal dust not efficiently neutralizing the acidic ions.
  • PMF resolved sources of chemical constituents of rainwater of the region.
  • Contributions from sea, agriculture, coal burning, biomass burning, crustal dust.


The chemistry of rainwater over mid-Brahmaputra Valley was studied for three consecutive years (2012–2014; n = 285). The samples were analyzed for major chemical parameters viz. pH, electrical conductivity (EC), and ions (SO42–, NO3, Cl, F, Br, Ca2+, NH4+, Mg2+, Na+, K+, and Li+), organic acids (HCOO and CH3COO) and dissolved organic carbon (DOC). The mean pH for the entire study period was found to be 5.66, which ranged from 4.51 to 7.68, and the volume weighted (VW) mean pH was found to be 5.16. Over 55% of the samples showed pH between 5 and 6, and a few samples had pH<5. Ionic concentration followed the order NH4+ > Ca2+ > SO42– > NO3 > Cl > Na+ > K+ > Mg2+ > H+ > HCO3 > Br > F > Li+, indicating dominance of alkaline ions over acidic ions such that 94% of mineral acid was neutralized. The secondary ions, NH4+, SO42–, and NO3, showed high wet deposition fluxes. The chemistry exhibits explicit seasonality. The airmass clusters of monsoon and non-monsoon seasons, and the associated chemistry varied, which showed influence of long-range transport. The interspecies correlations varied between the monsoon and non-monsoon time samples meaning variation in the source strengths of the contribution sources of the chemical species of the rainwater. Positive Matrix Factorization (PMF) was applied to the data which extracted six factors that explained the sources and chemistry of the rainwater constituents which are of sea, agriculture, coal burning, biomass burning, and secondary origin.

Keywords: Rainwater chemistry; Source apportionment; HYSPLIT Back trajectory; PMF.

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