Long-term (2007–2013) analysis of aerosol optical properties over four locations in the Indo-Gangetic plains

Abstract

The emphasis of the present work lies on the examination of the distribution and spectral behavior of the optical properties of atmospheric aerosols in the Indo-Gangetic plains (IGP). Measurements were performed using an AErosol RObotic NETwork (AERONET) Sun photometer at four sites (Karachi, Lahore, Jaipur, and Kanpur) with different aerosol environments during the period 2007-2013. The aerosol optical depth (AOD) and Ångström exponent (α) were measured, and the results revealed a high AOD with a low α value over Karachi and Jaipur in July, while a high AOD with a high α value was reported over Lahore and Kanpur during October and December. The pattern of the aerosol volume size distribution (VSD) was similar across all four sites, with a prominent peak in coarse mode at a radius of 4.0-5.0 μm, and in fine mode at a radius of 0.1-4.0 μm, for all seasons. On the other hand, during the winter months, the fine-mode peaks were comparable to the coarse mode, which was not the case during the other seasons. The single scattering albedo (SSA) was found to be strongly wavelength-dependent during all seasons and for all sites, with the exception of Kanpur, where the SSA decreases with increasing wavelength during winter and post-monsoon. It was found that the phase function of the atmospheric aerosol was high at a small angle and stable around a scattering angle of 90°-180° at all sites and during all seasons. Spectral variation of the asymmetry parameter (ASY) revealed a decreasing trend with increasing wavelength, and this decreasing trend was more pronounced during the summer, winter, and post-monsoon as compared to pre-monsoon. Furthermore, extensive measurements suggest that both real (RRI) and imaginary (IRI) parts of the refractive index (RI) show contrasting spectral behavior during all seasons. Finally, the analysis of the National Oceanic and Atmospheric Administration hybrid single particle Lagrangian integrated trajectory model back trajectory revealed that the seasonal variation in aerosol types was influenced by a contribution of air masses from multiple source locations.

Thirteen Years of Aerosol Radiative Forcing in Southwestern Iberian Peninsula

“…This wavelength dependence is more intense in winter than during the other seasons of the year, with mean values of 0.88 ± 0.08 at 440 nm and 0.80 ± 0.14 at 1020 nm. This dependence is also reported for Lahore and Karachi by Alam et al (2012), Delhi by Singh et al (2010), and four locations in the Indo-Gangetic plains by Bibi et al (2016), but only during winter, when dust is not a major contributor to the aerosol load.…”

Impacts of climate and synoptic fluctuations on dust storm activity over the Middle East

“…Because of the broad spatiotemporal coverage of the Moderate Resolution Imaging Spectroradiometer (MODIS), its AOD data have been widely used for examining spatial and temporal distribution of dust (Song et al, 2008; Schaap et al, 2009; Alam et al, 2010, 2011b; Huang et al, 2010; Sorooshian et al, 2011; Namdari et al, 2016; Sehatkashani et al, 2016). Several studies have addressed the relationship between dust and meteorological parameters (Zhao et al, 2004; Qu et al, 2006; Yang et al, 2007; Hui et al, 2008; Du et al, 2009; Kanniah and Yaso, 2010; Alam et al, 2012, 2014b; Yu et al, 2015; Bibi et al, 2016). Yang et al (2007), for example, analyzed dust storm events and their relation to climate change in Northern China during the past 1000 years by using different paleoclimate archives such as ice cores, tree rings, and historical documents.…”

Spectral and seasonal variations of aerosol optical depth with special reference to Kanpur, Indo-Gangetic Basin

“…where α is the Ångström exponent for AERONET in wavelength range between 0.44-0.87 µm and is a quantitative indicator of fine mode fraction or aerosol particle size. α is positively correlated with AOD over Kanpur (36) .…”