Volume 15, No. 3, June 2015, Pages 974-984 PDF(3.58 MB)
Morphology of Atmospheric Particles over Semi-Arid Region (Jaipur, Rajasthan) of India: Implications for Optical Properties
Sumit Kumar Mishra1, Rajesh Agnihotri1, Pawan Kumar Yadav1, Sukhvir Singh1, M.V.S.N. Prasad1, Puppala Siva Praveen2, Jai Shankar Tawale1, Rashmi1, Nidhi Dixit Mishra3, Bhuwan Chandra Arya1, Chhemendra Sharma1
1, CSIR-National Physical Laboratory, New Delhi, 110012, India
2, International Centre for Integrated Mountain Development, Kathmandu, GPO Box 3226, Nepal
3, Division of Environmental Sciences, Indian Agricultural Research Institute, New Delhi, 110012, India
- Effect of dust non-sphericity on scattering is significant for hematite rich dust.
- Equivalent sphere model may lead significant uncertainty in the retrieved SSA.
- Need of statistical representative database of particle shape proportions.
The regional dust morphology and spectral refractive indices (RIs; governed by hematite, Fe2O3 content at short wavelengths) are key elements for ascertaining direct radiative forcing of mineral dust aerosols. To provide morphological features of background mineral dust from a semi-arid zone in the vicinity of the Thar Desert, we carried out an expedition to the Jaipur city during late winter of 2012. Morphological analysis reveals the predominance of “Layered”, “Angular” and “Flattened” particles, while the frequency distribution of a total of 235 dust particles shows the aspect ratio, AR and circularity parameter, CIR (measures of particle’s non-sphericity) typically ~1.4 and ~0.8, respectively. Sensitivity analysis at 550 nm wavelength reveals the equivalent sphere model may underestimate Single Scattering Albedo, SSA for the dust with low (~1.1%) hematite by ~3.5%. Both underestimation (by ~5.6%) and overestimation (up to 9.1%) are probable in case of dust with high hematite content (~5.68%). In addition, the effect of AR on the dust scattering is significant in case of dust with high hematite content. More such regionally representative dust morphological data are required for better estimation of regional radiative forcing of mineral dust aerosols.
Dust; Morphology; Hematite; Refractive index; SSA.