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摘要
Aerosol hemispherical scattering and the bacicscattering coefficients, sigma(sp), sigma(bsc), have been measured using a 3-wavelength (450, 550 and 700 nm) integrating nephelometer over two years (January 2006-May 2008) in the coastal area of the Gulf of Cadiz, in the southwest of the Iberian Peninsula. These coefficients have been carefully analyzed starting with the impact of corrections on the measurements of sigma(sp): i.e., drift calibration constants do not modify the mean value in our data series. However, the selection of dry data (with RH less than 50%) modifies substantially the number of data and the resulting mean value of sigma(sp) is now 14% lower, which is compensated when the angular truncation correction is applied. The characterization and features of sigma(sp), sigma(bsc), and the derived parameters alpha(sp) (alpha Angstrom exponent) and b (the backscatter ratio) has been analyzed, as annual, seasonal and diurnal evolution. A general statistic based on hourly data gives mean values and standard deviation of asp (500 nm)=48 +/- 38 Mm(-1) with a median of 38 Mm(-1), and sigma(bsc) (500 nm)= 5.6 +/- 3.8 Mm(-1) with a median of 4.6 Mm(-1). Thus, these values show moderate-low values but with a large range of variation considering the existing measured values over the Iberian Peninsula. The median value of sigma(sp) (500 nm) is an indicator that events of high aerosol burden are frequent presenting a substantial influence on the daily averages. The alpha Angstrom exponent, alpha(sp), derived from the pairs 450/700 nm gives a mean value 135 +/- 0.54 with a median of 1.47 and with the most frequent value of 1.7, thus indicating the prevalence of medium size particles but with a significant influence of fine particles. The b ratio has the same value for mean and median, 0.12 +/- 0.02, showing a decrease with increasing values of sigma(sp). Annual and daily cycles have been also analyzed showing the complex behaviour of the optical properties at this coastal site where cold and warn periods show very different characteristics. Besides, the daily cycle is strongly influenced by the breeze conditions. According to the information extracted from the sigma(sp)-alpha(sp) relationship this rural Atlantic site presents prevalence of mixed marine-continental aerosols but with significant influence of local anthropogenic sources. Desert dust particles were also discriminated which are not frequently reported in the data of "in situ" aerosols.
- 出版日期2015-9
