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Gramsch E.,University of Santiago de Chile | Le Nir G.,University Paris Diderot | Araya M.,University of Santiago de Chile | Rubio M.A.,University of Santiago de Chile | And 2 more authors.
Atmospheric Environment | Year: 2013

In 2006 a large transformation was carried out on the public transportation system in Santiago de Chile. The original system (before 2006) had hundreds of bus owners with about 7000 diesel buses. The new system has only 13 firms with about 5900 buses which operate in different parts of the city with little overlap between them. In this work we evaluate the impact of the Transantiago system on the black carbon pollution along four roads directly affected by the modification to the transport system. Measurements were carried out during May-July of 2005 (before Transantiago) and June-July of 2007 (after Transantiago).We have used the Wilcoxon rank-sum test to evaluate black carbon concentration in four streets in year 2005 and 2007. The results show that a statistically significant reduction between year 2005 (before Transantiago) and year 2007 (after Transantiago) in Alameda street, which changed from a mean of 18.8 μg m-3 in 2005 to 11.9 μg m-3 in 2007. In this street there was a decrease in the number of buses as well as the number of private vehicles and an improvement in the technology of public transportation between those years. Other two streets (Usach and Departamental) did not change or experienced a small increase in the black carbon concentration in spite of having less flux of buses in 2007. Eliodoro Yañez Street, which did not have public transportation in 2005 or 2007 experienced a 15% increase in the black carbon concentration between those years. Analysis of the data indicates that the change is related to a decrease in the total number of vehicles or the number of other diesel vehicles in the street rather than a decrease in the number of buses only. These results are an indication that in order to decrease pollution near a street is not enough to reduce the number of buses or improve its quality, but to reduce the total number of vehicles. © 2012 Elsevier Ltd. Source

Carbone S.,Air Quality | Saarikoski S.,Air Quality | Frey A.,Air Quality | Reyes F.,Mario Molina Center for Strategic Studies in Energy and Environment | And 9 more authors.
Aerosol and Air Quality Research | Year: 2013

High time resolution chemical characterization of submicron particles was carried out in the South American city of Santiago de Chile using the Aerosol Chemical Speciation Monitor (ACSM). The instrumentation operated for 100 days from August 17thto November 23rd2011 in an urban station located inside the University of Santiago de Chile (USACH) campus. In addition, a semi-continuous OC/EC analyzer was also run in parallel with the ACSM for some of this time. Meteorological conditions varied along the studied period due to the transition from winter to spring time. Atmospheric temperature inversions were responsible for hourly average sub-micron particulate matter levels of up to 80 μg/m3, especially during the night time. The average submicron particle mass concentration (± standard deviation) for the whole period was 29.8 ± 25 μg/m3. Aerosol particles were composed mainly of organics 59%, followed by nitrate, ammonium, sulfate, black carbon and chloride with contributions of 14, 12, 8, 3 and 3%, respectively. Using positive matrix factorization, the organic fraction was divided into four distinct types of organic aerosol representing fresh automobile exhaust, biomass burning, and two oxygenated organic aerosol factors with different oxidation states. The transition from winter to spring was clearly seen in the composition of OA. The emissions from primary sources, such as vehicle and biomass burning, decreased in the period leading to spring, whereas the amount of oxygenated organic aerosol increased over the same time. This study shows that high time resolution measurements of aerosol chemical composition can lead to better characterizations of the evolution and sources of pollutants in an urban atmosphere. © Taiwan Association for Aerosol Research. Source

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