Retrieval of Aerosol Properties from Surface Measurements in an Urban Environment

Received: September 25, 2013
Revised: December 22, 2014
Accepted: February 10, 2014
Download Citation: RIS|BibTeX|https://doi.org/10.4209/aaqr.2013.09.0294  

Cite this article:
Alam, K., Madl, P., Trautmann, T., Blaschke, T. and Iqbal, M.J. (2014). Retrieval of Aerosol Properties from Surface Measurements in an Urban Environment. Aerosol Air Qual. Res. 14: 686-696. https://doi.org/10.4209/aaqr.2013.09.0294

ABSTRACT

Aerosol optical and radiative properties have, for the first time, been retrieved from ground-based measurements in Karachi, Pakistan. Ground-based aerosol measurements were obtained using a GRIMM Model 1.109 optical particle counter (OPC). The optical and radiative properties of aerosols were retrieved from these measurements using the Aerosol Robotic Network (AERONET) inversion algorithm.  

The volumetric size distribution obtained from the OPC measurements shows three distinct modes, one fine and two coarse, with a fine mode particle diameter of about 0.29 µm and coarse mode particle diameters of about 7 µm and 22.5 µm. An overlap in between the size range of 0.25 µm to 7 µm has been carried out by using OPC data together with data obtained from AERONET. The obtained OPC-transposed data set (OPC_AOD) was compared with those obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite and AERONET Sunphotometer. The analysis revealed a moderate correlation of 0.57 between OPC_AOD and MODIS_AOD data but only low correlations between OPC_AOD and AERONET_AOD data (0.21), and between MODIS_AOD and AERONET_AOD data (0.26).

The Single Scattering Albedo (SSA) for the measurement days, calculated at a wavelength of 676 nm, ranged from 0.83 ± 0.01 to 0.90 ± 0.02, showing slight variations in magnitude between the different measurement days. The asymmetry parameter (ASY), a wavelength-dependent quantity, was calculated for the same wavelength yielding values that ranged from 0.59 ± 0.01 to 0.68±0.02. The aerosol radiative forcing (ARF) values measured for the period of observation at the top of the atmosphere, at the earth's surface, and within the atmosphere ranged from 31.2 Wm^–2 to –28.27 Wm^–2, from –69.76 Wm^–2 to –73.57 Wm^–2, and from 38.56 Wm^–2 to 45.3 Wm^–2, respectively.

Keywords: AOD; AERONET; MODIS; Pakistan; Radiative forcing; GRIMM-OPC