In this study, it is reported the fractal dimension and morphology of ultrafine particles emitted by a diesel engine run with B4, B50, and B100. Transmission electron micrographs evidenced two main groups of particles with characteristic and distinct morphological behaviors: (i) particle agglomerate structures self-organized within a fractal-like geometry, and (ii) amorphous and irregular particles with diffuse edges in a liquid-like particle appearance, mainly associated with some sub-fractions of samples collected from B50 and B100 combustion. Particles from (i) showed typical diesel soot morphology and fractal dimension. Primary particle diameter (Dpp) was 24 ± 4 nm, 23 ± 4 nm, and 20 ± 4 nm for B4, B50, and B100, respectively. Mean aggregate gyration diameters (Dg) ranged from 242 ± 140 nm for B4, 210 ± 135 nm for B50, and to 232 ± 140 nm for B100. In turn, fractal dimensions (Df) were 1.94, 1.89, and 1.99 for B4, B50, and B100, respectively. On the other hand, particle from (ii) had their morphology impaired from the addition of biodiesel to petrodiesel in a way it did not follow a fractal geometry.

Repartimos a parcela do componente de carbono elementar (CE) em PM2,5 atmosférico atribuível à emissões de veículos com ignição por faísca (SI) em amostras coletadas durante dois anos em doze comunidades no Sul da Califórnia, incluindo zonas costeiras, rurais e urbanas usando o Modelo de Balanço de Massa Química (CMB8) modificado para levar em conta a reatividade dos hidrocarbonetos policíclicos aromáticos (HPAs). Foram avaliadas as razões HPA/CE em amostras coletadas no túnel Caldecott para utilização como assinaturas das fontes. A reatividade dos HPAs que ocorre durante o transporte de aerossóis atmosféricos que pode afetar as estimativas de contribuição das fontes (ECF) durante o verão/primavera/outono foi considerada com o uso de constantes de decaimento medidas experimentalmente. Nossos resultados mostram que o benzo[ghi]perylene e o indeno[1,2,3-cd]pireno podem ser utilizados com sucesso como marcadores específicos de CE nas emissões por veículos com SI. A estimativa média da porção de CE atribuído pelo modelo à emissões provenientes de SI nessas comunidades foi de 39, 58 e 62%, respectivamente, durante o verão, primavera/outono, e inverno. Para todas as comunidades costeiras, as atribuições a veículos por SI representam cerca do dobro das estimativas para as áreas rurais e urbanas, antes de dezembro 2003 quando MTBE ainda era usado na California.

We apportioned the elemental carbon (EC) component of ambient PM2.5 attributable to emissions from spark ignition (SI) vehicles in samples collected over a three-year period in twelve Southern California communities, including coastal, rural, and urban areas using the chemical mass balance model (CMB8) modified for polycyclic aromatic hydrocarbon (PAH) reactivity. Selected PAH/EC ratios, measured in samples collected in the Caldecott tunnel were evaluated for use as fingerprints. PAH reactivity which occurs during atmospheric transport and affects the source contribution estimates during the summer/fall/spring months was accounted for using experimentally measured decay constants. Results showed that benzo[ghi]perylene and indeno[1,2,3-cd]pyrene can be used successfully as specific tracers of EC contributions from SI vehicles. The average EC portion of PM2.5 attributed by the model to SI emissions at these communities was 39, 58 and 62%, respectively, during the summer, spring/autumn, and winter. For all seasons, coastal community contributions represent about twice those found in the rural and urban inland communities, before December 2003 when MTBE was still in use in California.