Water Soluble Ionic Components in Particulate Matter (PM10) during High Pollution Episode Days at Mohal and Kothi in the North-Western Himalaya, India

ABSTRACT

Particulate pollutants and their water soluble ionic components were collected and analyzed on the occasion of high pollution episode days in the period 2009 to 2011. Among the water soluble ionic constituents at Mohal (valley base), SO₄^2– (34%) was the largest contributor; followed by Cl^– (20%), NO₃^– (17%), Ca²⁺ (9%), Na⁺ (7%), NH₄⁺ (5%), F^– (2%), Zn²⁺ (2%) and Mg²⁺ (1%). While at Kothi (hill slope), Cl^– (27%) was the largest contributor; followed by SO₄^2– (25%), NO₃^– (14%), Na⁺ (11%), Ca²⁺ (9%), NH₄⁺ (7%), K⁺ (3%), F^– (3%) and Zn²⁺ (1%). The average ratios of NO₃^– + Cl^–/SO₄^2– were 1.08 and 1.64 for Mohal and Kothi, respectively; indicating that a small fraction of HNO₃ and HCl influenced the acidic nature of ions. The mass ratios of NH₄⁺/NO₃^– and NH₄⁺/SO₄^2– were 0.29, 0.5 and 0.15, 0.28; at Mohal and Kothi, respectively. The ratios were below unity showing the predominance of NH₄NO₃ and (NH₄)₂SO₄ in the atmosphere. The descending order of neutralizing factors were observed as Ca²⁺ > NH₄⁺ > K⁺ > Mg²⁺ assuming that the origin is of a crustal source. The non-sea salt fraction for Mohal was found in the descending order of Cl^–, Ca²⁺ and SO₄^2–, which are more than 50% of the total ions except Mg²⁺ and K⁺. While for Kothi, the percentage of Cl^– and SO₄^2– stood to be more than 50% indicating that these ions are of non-marine origin. The first factor from principal component analysis for Mohal explains 75.59% of the total variance i.e., highly loaded with NH₄⁺ (0.986), K⁺ (0.685), F^– (0.935), Cl^– (0.919) and Zn²⁺ (0.969) indicating influence of anthropogenic activities on PM₁₀ concentration. While at Kothi, the first factor explains 45.41% of the total variance, highly loaded with K⁺ (0.981), SO₄^2– (0.965), NO₃^– (0.953) and Zn²⁺ (0.948) also indicating influence of anthropogenic activities in the region.