Aerosol optical properties measured in Argentina: wavelength dependence and variability based on sun photometer measurements

P. RISTORI, L. OTERO, J. FOCHESATTO, P. H. FLAMANT, E. WOLFRAM, E. QUEL, R. PIACENTINI, B. HOLBEN, C. MCCLAIN

Optics and Lasers in Engineering

ELSEVIER

Año: 2003 vol. 40 p. 91 - 104

0143-8166

This paper deals with the spectral dependence and time variability of Ångström wavelength exponent scaling law (a), which is the spectral varying slope of the logarithm relationship between aerosol optical depths (t) and the wavelength (l). It is commonly used to retrieve intensive air masses optical properties such as aerosol size distribution from extensive quantities as (t) and Ångström turbidity coefficient (b). This spectral variation of (a) was study at different wavelength from measurements takes by ground based sun photometer covering from near infrared to ultraviolet range. We analyze the spectral measurement of aerosols optical depths at eight specific selected wavelengths from (340 nm to 1020 nm) using the sun photometer measurements from AERONET AErosol RObotic NETwork from NASA. Data from the entire 2000 was used from instruments deploys at two different sites covering the regions of Argentine as north-central at Cordoba CETT (31.5S, 64.4W) and “pampa húmeda” at Buenos Aires CEILAP (34.5S,58.5W). A new approach of Ångström wavelength exponent spectral variation was developed to take into account with a more accurate precision the significant curvature appears in the logarithmic relation between (t) and (l). Using the direct spectral solar radiation set, time series of Ångström coefficient of turbidity and wavelength scaling law, was computed with a day to day data base clustering with uncertainty lower than 0.01 in the optical depth reconstruction over the bulk sun photometer measurements. Temporal series of constant and spectral dependence of wavelength exponent scaling law and turbidity coefficient was derived and showed to varying in space and time. Different meteorological forcing for both sites was evidenced using a regression coefficient analysis to well assess the spectral dependence of wavelength exponent coefficient dues to the different cumulating mode of particles and air masses origin at different sites. This spectral decomposition is a key issue in aerosols analysis of steady state and regional scale intrusion episodes with strong connection with their potential contribution of pollution episodes in air quality problems on urban environment.