Columnar characteristics of aerosols by spectroradiometer measurements in the maritime area of the Cadiz Gulf (Spain)

Abstract

Atmospheric aerosol characteristics represented by the spectral aerosol optical depth AOD) and the αÅngström turbidity parameter were determined in the coastal area of the Gulf of Cádiz, (southwest of Spain). The columnar aerosol properties presented here correspond to the 1996-1999 period, and were obtained by solar direct irradiance measurements carried out by a Licor1800 spectroradiometer. The performance of this type of medium-spectral resolution radiometric system is analysed over the measured period. The detailed spectral information of these irradiance measurements enabled the use of selected non-absorption gases spectral windows to determine the columnar spectral AOD that was modelled byÅngström formula to obtain the α coefficient. Temporal evolutions of instantaneous values together with a general statistical analysis represented by seasonal values, frequency distributions and some representative correlations for the AOD and the derived αÅngström coefficient gave us the first insight of aerosol characteristics in this coastal area. Special attention was paid to the analysis of these aerosol properties at the nominal wavelengths of 440 nm, 670 nm, 870 nm and 1020 nm for the near-future comparisons with the Cimel sun-photometer data. However, taking the most representative aerosol wavelength of 500 nm, the variability of the AOD ranges from 0.005 to 0.53, with a mean of 0.12 (s.d = 0.07) and that of the α parameter is given by a mean value of 0.93 (s.d. = 0.58) falling inside the range of marine aerosols. A quantitative discrimination of aerosol types was conducted on the basis of the spectral aerosol properties and air mass back trajectory analysis, which resulted in a mixed type because of the specificity of this area, given by very frequent desert dust episodes, continental and polluted local influences. This study represents the first extended data characterization about columnar properties of aerosols in Spain which has been continued by Cimel-AERONET data.

Study of desert dust events over the southwestern Iberian Peninsula in year 2000: two case studies

“…The highest levels are particularly suited for desert aerosol assessment (Vergaz, 2001;Rodriguez et al, 2001;Querol et al, 2002a, b). From an inspection of these trajectories, we assign those arriving from North Africa as desert dust episodes, which allows an evaluation of the episodes and number of dusty days during 2000 (Vergaz, 2001;Vergaz et al, 2005). Additionally, synoptic weather maps were obtained from the NOAA FLN data set (http://www.arl.noaa.gov/ready/ amet.html) at the 700 hPa, 850 hPa and surface levels as complementary information for the two case studies.…”

“…With the AOD and α criteria, we have 14 events with a total of 27 days. We can also evaluate desert dust episodes by means of back-trajectory analysis, taking the levels there and assigning those with a clear origin over a geographical sector covering North Africa (for details, see Vergaz, 2001;Vergaz et al, 2005). For 2000 (not including January) at El Arenosillo, there were 21 desert events with a total of 60 days.…”

Column-integrated aerosol microphysical properties from AERONET Sun photometer over southwestern Spain

“…In previous works (Vergaz et al, 2005;Toledano et al, 2007a) the columnar aerosol properties at El Arenosillo area were characterized by means of the aerosol optical depth (AOD) and theÅngström exponent (AE). Both parameters are well known in the field of atmospheric aerosol studies and represent the first key properties for the aerosol characterization, giving information about the load and the predominant size of the aerosol.…”

Identification of aerosol types over an urban site based on air-mass trajectory classification

“…Back-trajectory analysis was employed to qualitatively link variations in the chemical and optical properties of aerosols to sources like broadly biomass burning and fossil fuel combustion located in geographical regions traversed by air masses arriving in the Arabian Sea and tropical Indian Ocean (Reiner et al, 2001;Mayol-Bracero et al, 2002;Quinn et al, 2002;Franke et al, 2003). Examples may include quantifying ground-level aerosol concentrations (Sa´nchez et al 1990;Rodriguez et al 2001), examining the relationship between air-mass history and trace elements (Bahrmann and Saxena 1998;Cape et al 2000;Methven et al 2001) and investigating the relationship between airmass type and AOD (Vergaz et al, , 2005Estelle´s et al, 2007). Many other studies A C C E P T E D M A N U S C R I P T…”