4. Conclusions
This study is a precursor one in the evaluation of atmospheric
nanoparticles in Porto Alegre, southern Brazil. Six sampling sites
(one urban background, two roadsides, two traffic intersections,
and one street canyon) were evaluated, and PNC was observed in
the following descending order: traffic intersection > street canyon
> roadside > urban background. The PNC levels were similar to
some developing countries where the major source of problem is
vehicular. The high PNCs observed in this study, especially when
compared with those observed in most countries in Europe, were
primarily caused by the high sulfur content in the Brazilian fuel and
by the age of the fleet in circulation. The results revealed that PND
is characterized by three modes: mode–1 (nucleation), mode–2
(Aitken), and mode–3 (accumulation). Size distributions were
dominated by nucleation (44.9%) and Aitken (42.0%) modes being
representative for local sources near the vehicle exhaust. In this
study nucleation and Aitken mode particles were especially
originated from primary sources at all study sites, except the urban
background. At this site, nucleation mode particles were formed
from secondary sources through photochemical and chemical
reactions during the warmer days. The relative contributions of
cold and hot days for some studied sites were not very clear due to
the lack of measurements. The study showed that besides the local
meteorological parameters, there was a great influence of
meteorological conditions of synoptic scale on PNC and PND.
Future studies will include daily and seasonal variations to better
understand the mechanisms of nanoparticle formation. Furthermore,
some pollutants such as NOX and CO will also be evaluated
as they are indicators of emissions from combustion sources.