Physical and optical properties of aerosols over an urban location in Spain: seasonal and diurnal variability

Abstract

Abstract. Measurements of aerosol optical properties and aerosol number size distribution obtained during the period from December 2005 to November 2007 at Granada, an urban site in south-eastern Spain, are analyzed. Large variations of the measured variables have been found, and related to variations in emissions sources and meteorological conditions. High values of aerosol absorption and scattering coefficients are obtained during winter and low values are measured during summer. This seasonal pattern in the surface aerosol optical properties is opposite to the seasonal cycle showed by columnar aerosol optical depth. The differences in the seasonal features of the surface and column-integrated data are related to seasonal variations in the aerosol vertical distribution, aerosol sources and boundary layer height. In winter the number density of "fine" particles (0.5<particle diameter<1 µm) is significantly larger than in summer while the number density of "coarse" particles (1<particle diameter<20 µm) is slightly larger during summer and spring than during winter and autumn. The scattering Angström exponent, α s , presents an evident seasonal cycle with values of 1.8±0.2, 1.6±0.3, 1.3±0.3 and 1.4±0.3 in winter, spring, summer and autumn, respectively. This suggests the presence of a large fraction of submicron particles at the site, especially during winter. The aerosols measured in this study contain a large fraction of absorbing material as indicated by the average single-scattering albedo that has values of 0.65±0.07, 0.66±0.06, 0.70±0.06 and 0.73±0.06 in autumn, winter, spring and summer, respectively. The aerosol scattering albedo obtained in the surface boundary layer of Granada is below the critical value of 0.86 that determines the shift from cooling to warming. These Correspondence to: L. Alados-Arboledas (alados@ugr.es) results put in evidence the need of efforts to reduce absorbing particles (black carbon) emissions to avoid the possible warming that would result from the reductions of the cooling aerosols only. The aerosol absorption and scattering coefficients present a clear diurnal pattern, in all seasons, with two local maxima, one early in the morning and the second one in the evening. This diurnal cycle is mainly attributed to the diurnal evolution of atmospheric boundary layer and local anthropogenic activities.

Study of mineral dust entrainment in the planetary boundary layer by lidar depolarisation technique

“…Main local aerosol sources are road traffic, soil re-suspension (especially during the warm-dry season) and domestic heating based on fuel-oil combustion during winter (Titos et al, 2012, Titos et al, 2014a. Main external aerosol sources are the Sahara Desert located at 500 km southward as well as industrial and urban areas in Europe (Lyamani et al, 2010).…”

Spatial and temporal variability of carbonaceous aerosols: Assessing the impact of biomass burning in the urban environment

“…Atmospheric aerosol optical properties have been widely investigated in the city of Granada at surface level (e.g., Lyamani et al, 2008;Lyamani et al, 2010;Titos et al, 2012;Segura et al, 2014), in the vertical column with height resolution (e.g., GuerreroRascado et al, 2008;Alados-Arboledas et al, 2011;Bravo-Aranda et al, 2015 and references therein) and column-integrated (e.g., Lyamani et al, 2005;Valenzuela et al, 2012). The meteorological conditions together with the topography of the city sited in a valley surrounded by mountains of high elevation (about 3500 m a.s.l.)…”

Aerosol Optical Depth measurements at 340 nm with a Brewer spectrophotometer and comparison with Cimel sunphotometer observations at Uccle, Belgium

“…In Valencia (Spain), maximum AOD values were observed (between 2002-2005) from June to September, whereas the minimum values occurred from October to February (mainly in December and January) (Estellés, 2008). Behnert et al (2004) Granada (Spain), M'Bour (Senegal), Gwangju (Korea) and Thessaloniki (Greece) also show high AOD values in summer and low values in winter (Meleti and Cappellani, 2000;Kim et al, 2006;Kazadzis et al, 2007;Léon et al, 2009;Lyamani et al, 2010). (The latitude and longitude of the places mentioned in this article can be found in Table 2.…”

“…Both Bäumer et al (2008) and Xia et al (2008) reported a weekly cycle in AOD for Central Europe (45-55 • N; 0-20 • E). Seasonal patterns in AOD with maximum values in spring and summer and minimum values in autumn and winter are observed in many studies (Meleti and Cappellani, 2000;Behnert et al, 2004;Kim et al, 2006;Estellés, 2008;Remer et al, 2008;Che et al, 2009;Léon et al, 2009;Lyamani et al, 2010). Gröbner and Meleti (2004) studied long-term trends in AOD at Ispra and detected a decrease between 1991 and 1997, followed by a stabilization in the AOD values.…”

“…They affect the tropospheric chemical composition, they can reduce visibility and they have important impacts on human health (Unger et al, 2009;Lyamani et al, 2010;Raghavendra Kumar et al, 2010). Aerosols also influence the Earth's radiation budget in a direct, semi-direct and indirect manner.…”