Sources and factors affecting aerosol acidity in the Eastern Indo-Gangetic Plain

Anurag, Polana (2019) Sources and factors affecting aerosol acidity in the Eastern Indo-Gangetic Plain. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Aerosol acidity is defined as the amount of free ambient H⁺ present in the particulate phase in the atmosphere. It is important to study aerosol acidity as it is actively involved in aerosol chemistry and increasing aerosol acidity can enhance the chance of acidic precipitation which deteriorates the environment. This report presents the seasonal variability of water-soluble inorganic species (WSIS) and water-soluble organic carbon (WSOC) in ambient PM₂.₅ (aerosols with aerodynamic diameter ≤ 2.5 μm) sampled at a rural site (Mohanpur) in the Eastern Indo-Gangetic Plains. A total of 88 24h samples were collected across summer, post monsoon and winter. A total of 10 WSIS (SO₄⁻², NO₃⁻, Cl⁻, Na⁺, NH₄⁺, K⁺, Ca⁺², Mg⁺²,F⁻ and PO₄⁻³) were analysed using ion chromatography technique and WSOC was measured using a TOC analyser. WSIS concentrations are increasing from summer to winter with a value of 13.79±3.05 μg m⁻³ in summer, 21.56±9.48 μg m⁻³ in post monsoon, 34.80±10.80 μg m⁻³ in winter respectively. Across all seasons aerosol phase was dominated by SO₄⁻², NO₃⁻ and NH₄⁺. In summer the concentrations of SO₄⁻², NO₃⁻ and NH₄⁺ were 6.38±1.95 μg m⁻³, 1.10±0.71 μg m⁻³, and 1.96±0.68 μg m⁻³, respectively. In post monsoon the values of SO₄⁻², NH₄⁺ and NO₃⁻ have increased by a factor of 1.8, 1.4 and 1.8. For winter they have increased by a factor of 1.9, 2.9 and 11, respectively. NH₄⁺ was observed to be the major neutralizing agent across all seasons. In cases where NH₄⁺ is less K⁺ is responsible for neutralizing the excess acidity. WSOC instead of being catalysed by H⁺ is found to contributie to increased aerosol acidity in winter and post monsoon. A major role in this regard is played by biomass burning during post monsoon and winter, which contributes to enhanced levels of K⁺and WSOC.

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