Chemical identification of semi-urban aerosols by laser raman spectroscopy

Atmospheric aerosols play an important role in local, regional meteorology, visibility, air
pollution, haze formation and energy balance of radiation. These processes influence the
climate directly or indirectly. Therefore, for increasing importance of aerosols in understanding
the various environmental processes and public health; it is necessary to have accurate
physical and chemical identification of these aerosols. The Raman scattering has only
recently been demonstrated as potential analytical method for chemical identification of
aerosol particles [1], [2]. This technique is used for the chemical identification of aerosol at
Ahmednagar (INDIA). Various spectroscopic techniques have been applied for the
identification of the matter, while most of these techniques can be adopted as a routine
analytical procedures for bulk samples. They may not be practical for aerosol samples at all.
Each of these techniques has its advantages and disadvantages. For in situ identification of
aerosol particles, however, Raman scattering is currently the most promising technique. It has
small scattering cross-section but large number of advantages. We have explored the use of
Raman Spectroscopy for the identification of aerosol particles of urban, rural, and industrial
areas. The aerosol samples are collected on pure quartz filters with high volume aerosol
sampler and Raman spectra is obtained using Raman spectrometer. It uses double
monochromator with diffraction grating having 1800 grooves/mm and diode laser (532nm
wavelength) with 25mW Power. The spectra of aerosol samples are collected in the
perpendicular direction to the incident laser beam from the surface of filter containing
aerosols. Thus, the various aerosol samples have been investigated for their chemical
speciation. The Raman spectra for atmospheric aerosols appears in the region 607cm-1 to
937cm-1. The peaks at 607cm-1and 647cm-1 [3] correspond to Ammonium sulphate and
Ammonium bicarbonates present in environmental aerosols respectively. In addition to this
the Raman shifts at 847cm-1and 937cm-1are equivalent to potassium bisulphate and
potassium chlorate. These are the major chemical species present in the semi-urban
environment of Ahmednagar city. This region is dominated by low rainfall; dry weather and
having relative humidity around 40%. The region is surrounded by the agriculture land
producing sugarcane as a major agriculture crop. Hence, the aerosol chemical identification
of this region would be an additional contribution to the data on aerosols.