In situ measurements of aerosol extinction profiles and their spectral dependencies at tropospheric levels

Aerosol extinction coefficients are measured using rocket and balloon-borne photometers from Thumba (8.5°N) and Hyderabad (17.5°N) respectively, in southern India. The spectral bands are selected within the 300 to 900 nm wavelength region. The aerosol extinction coefficients are found to exhibit large temporal and spatial variations. The spectral dependence of aerosol extinction, derived using a simple Angström power law shows that the wavelength exponent parameter α is altitude dependent. The data are grouped into 2 categories, to study the seasonal variations, in aerosol parameters before and after the Indian monsoon. In general, the premonsoon tropospheric aerosol extinction coefficients are found to be higher compared to the postmonsoon values. Furthermore, a layer characterized by a low α value, situated around 13 km in most of the premonsoon data, is found to come down to about 11 km after the monsoon with a corresponding increase in α.