Carbonaceous and Secondary Inorganic Aerosols during Wintertime Fog and Haze over Urban Sites in the Indo-Gangetic Plain

Received: July 22, 2011
Revised: February 15, 2012
Accepted: February 15, 2012
Download Citation: RIS|BibTeX|https://doi.org/10.4209/aaqr.2011.07.0105  

Cite this article:
Ram, K., Sarin, M., Sudheer, A. and Rengarajan, R. (2012). Carbonaceous and Secondary Inorganic Aerosols during Wintertime Fog and Haze over Urban Sites in the Indo-Gangetic Plain. Aerosol Air Qual. Res. 12: 359-370. https://doi.org/10.4209/aaqr.2011.07.0105

ABSTRACT

The chemical composition of total suspended particulate (TSP) matter and secondary aerosol formation have been studied during wintertime fog and haze events from urban sites (Allahabad and Hisar) in the Indo-Gangetic Plain. The atmospheric abundances of elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC) suggest that organic matter is a major component of TSP, followed by concentrations of sulphate and nitrate under varying meteorological conditions. The concentrations of EC, OC, and WSOC show a nearly 30% increase during fog and haze events at Allahabad and a marginal increase at Hisar; whereas inorganic constituents (NH₄⁺, NO₃⁻ and SO₄²⁻) are 2–3 times higher than those during clear days at both the locations. The sulphur and nitrogen oxidation ratios (SOR and NOR) also exhibit significant increases suggesting possible enhancement of secondary formation of SO₄²⁻ and NO₃⁻ during fog and haze events. The significant correlation between NH₄⁺–SO₄²⁻ (R² = 0.66, n = 61) and an NH₄⁺/SO₄²⁻ equivalent ratio ≥ 1 during fog-haze conditions suggest near-complete neutralization of sulphuric acid by ammonia. In contrast, NH₄⁺/SO₄²⁻ equivalent ratios are less than 1 during normal days suggesting an NH₃-deficient environment and the possible association of SO₄²⁻ with mineral dust for neutralization. Secondary inorganic aerosol formation and their hygroscopic growth can have significant impact on atmospheric chemistry, air-quality and visibility impairment during fog-haze events over northern India.

Keywords: Elemental carbon; Organic carbon; Secondary inorganic aerosols; Sulphur and nitrogen oxidation ratios; Fog and haze; Indo-Gangetic Plain