Black carbon and fine aerosol particles characterization at different environmental conditions in the Southeast of the Iberian Peninsula

Abstract

This PhD dissertation focuses on the characterization of fine atmospheric aerosol particles emission sources (their strength, spatial and temporal variability) at different environments by means of ground-based in-situ techniques. To this end, the aerosol microphysical and optical properties obtained by state-of-the-art instrumentation in multiple experimental campaigns performed at different environments (urban, suburban and remote high-altitude) in the southeast of the Iberian Peninsula have been analyzed and discussed. In order to take insight about the sources of fine atmospheric aerosol, their diurnal, weekly, seasonal and spatial variability in the Granada urban area, the aerosol number flux and concentration of fine particles obtained by eddy covariance technique are examined during the period from Nov/2016 to Apr/2018. The results show that the majority of aerosol number flux values are positive, suggesting that the urban site acts as a net source of aerosol particles to the atmosphere at different time scales. Concerning aerosol emissions sources, road traffic is identified as the main source in Granada urban area in all seasons. During winter, domestic heating and agricultural waste burning emissions are additional aerosol sources, while during spring and summer new particle formation processes contribute significantly to ultrafine aerosol particles. Wind sector analysis shows that the impact of domestic heating emissions from the urban area, especially at night, is much stronger than the impact of agricultural waste burning emissions from the suburban sector. With the aim to disentangle the contribution of the different aerosol sources to the total aerosol number concentration at sites influenced by biomass burning emissions, a new approach based on the Rodriguez and Cuevas (2007) and Sandradewi et al. (2008) methods has been developed. This new approach has been used to determine the contributions of both vehicle and biomass burning primary emissions and secondary aerosol to the size-segregated particle number concentrations at urban and suburban sites. This method has been applied to simultaneous measurements of aerosol number size distribution in the 12–600 nm size range and black carbon (BC) concentration obtained at both sites during winter season, when the study area is usually influenced by biomass burning emissions from domestic heating and agricultural waste burning. The results show that (1) secondary aerosol is the main contributor to the particle number concentration in all size ranges at both sites, (2) primary vehicle exhaust is the main source of primary particles with contributions >70% in all size ranges at both sites and (3) primary biomass burning particles contribute significantly to the primary particles concentrations in the 25–100 and 100–600 nm size ranges at the suburban (24% and 28%, respectively) and urban (13% and 20%, respectively) sites. In addition, new particle formation (NPF) events have been found to be an important aerosol source during summer noon hours but, on average, these events do not implicate a considerable contribution to urban particles. Despite this low contribution of NPF events to the total particle number concentration in Granada urban area, these events are of great importance for the production of cloud condensation nuclei (CCN), affecting clouds formation. Therefore, the characterization of NPF vertical distribution is of special interest. To this end, a detailed investigation of the NPF characteristics and the different factors that promote/inhibit NPF processes has been performed at two contrastive sites: urban and high-altitude remote sites. For this, simultaneous measurements of aerosol size distributions (4-500 nm) measured at both sites have been used. The analysis shows that, with NPF event frequency >70% at both sites, nucleation mode particles highly contribute to the total aerosol number concentration in summer (47 % and 48 % at mountain and urban sites, respectively). At the high-altitude remote site, NPF events have been found to be associated with the transport of gaseous precursors from lower altitudes by orographic buoyant upward flows. Nevertheless, NPF events at the high-altitude remote site have been always observed from the smallest measured sizes of the aerosol size distribution (4 nm), implying that NPF takes place in or in the vicinity of the high-altitude remote station rather than being transported from lower altitudes. Although NPF events at the mountain site seem to be connected with those occurring at the urban site, growth rates (GRs) at mountain site are higher than those at the urban site. The analysis of sulfuric acid (H2SO4) shows that the concentrations of H2SO4 can explain a minimal contribution of the observed GRs at both sites (< 1 % and < 10 % for the 7–25 and 4–7 nm size ranges, respectively), indicating that other condensing vapours are responsible for the majority of particle growth, as well as the differing growth rates between the two sites. The results also show that the condensation sink (CS) does not play a relevant role in NPF processes at both sites and points to the availability of volatile organic compounds (VOCs) as one of the main factors controlling the NPF events at the urban and high-altitude remote sites investigated.