Clear-sky direct aerosol radiative forcing variations over mega-city Delhi

Abstract

Abstract. The direct aerosol radiative forcing (DARF) has been estimated for the clear-sky conditions over Delhi from January 2006 to January 2007 using Santa Barbara DISORT Atmospheric Radiative Transfer model (SBDART) in the wavelength range 300-3000 nanometer. The single scattering albedo (SSA) and the asymmetry parameter used in this model were estimated using the Optical Properties of Aerosol and Cloud (OPAC) model. The annual average AOD observed at 500 nm was ∼0.86±0.42 with an average Angstrom exponent ∼0.68±0.35. The average monthly AOD throughout the year over Delhi was found to be in the range 0.56 to 1.22 with the Angstrom exponent in the range 0.38 to 0.96. A high monthly average BC concentration in the range 4-15 µg m −3 led to monthly average SSA in the range 0.90±0.4 to 0.74±0.3 during the year. Consequently, the monthly average clear-sky DARF at the surface was found to vary in the range −46±8 W m −2 to −110±20 W m −2 , at TOA in the range −1.4±0.4 to 21±2 W m −2 , whereas in the atmosphere it was in the range 46±9 W m −2 to 115±19 W m −2 throughout the year. As the dust concentration in the atmosphere was highest (May-June) the SSA showed an increase with wavelength however when dust concentration was low the SSA decreased with the wavelength.

Technical Note: One year of Raman-lidar measurements in Gual Pahari EUCAARI site close to New Delhi in India – Seasonal characteristics of the aerosol vertical structure

“…Our AE values are also in the same range than those presented by Niranjan et al (2007a, b) and Franke et al (2003). Singh et al (2010) reported the yearly variation of AE ext in Delhi to be between 0.38 and 0.96. These values are bit smaller than our seasonal averages (0.71-1.43).…”

Simulation of aerosol optical properties over a tropical urban site in India using a global model and its comparison with ground measurements

“…In order to improve the model simulations, measurements of both BC and aerosol optical information are required. Several studies on continuous and simultaneous measurements of both BC and aerosol optical information over the South-Asian region are reported in literature (Ganguly et al, 2006;Sreekanth et al, 2007;Safai et al, 2007;Gadhavi and Jayaraman, 2010;Singh et al, 2010). Validation studies on aerosol model simulations with these measurements has been less attempted in this region except for few studies (Adhikari et al, 2007), which validated their simulation results with the observed ones over South Asia during almost one year.…”

“…During these two winter months, lower values of BC are observed compared to simulations using the modified BC emission. Previous studies over Hyderabad (Latha and Badarinath, 2005) as well as over India (Sreekanth et al, 2007;Rastogi and Sarin, 2009;Singh et al, 2010) suggest that the variation of measured BC is minimum during the wet season and maximum during winter even though the magnitude of the BC concentration varies in the year due to anthropogenic factors. These factors may cause some difficulties both in making a corrected monthly variation in BC emission inventory for each year and thus in simulating BC aerosol distributions.…”

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.…”