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Characterisation of particulate matter in urban air: instrumentation development and experimental results
Gepubliceerd door: Publicatie datum:
ECN SF 1-4-2000
ECN publicatienummer: Publicatie type:
ECN-R--00-001 Overig
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The general aim of the project is the assessment of the effect ofemissions from traffic on the air quality in urban agglomerations (and on climate) and the determination of the cost and benefits of various possible local measures. In this report the results of the first part of the project are described. Traffic emissions contribute to a large extent to the health effects of air pollution. lt is still uncertain in which way these effects are related to aerosol mass, chemical composition or number density. Accurate measurements are highly desirable but relatively scarce due to technical difficulties. The need for technical refinements of the current sampling and analysis techniques of particulate matter is motivated. The temperature dependence of the accuracy of the TEOM measurement technique, the installation for the weighing of aerosol material under temperature controlled conditions, the technical improvements of the particulate carbon monitor for soot measurements, and the further improvement of the Steam-Jet Aerosol Collector (SJAC) are highlighted in this report. The improved techniques were implemented in a number of field campaigns yielding data on the influence of traffic emissions on PM concentration levels. The report here includes: (1) direct measurement of particulate matter in exhaust gases of passenger cars, (2) measurements of aerosol number and mass concentrations in a traffic tunnel, and (3) measurements in an urban environment at a fixed location or by means of a moving unit. The evaporation of ammonium nitrate as a function of the temperature of the heated filter in a TEOM demonstrates the need for temperature-controlled measurements and raises questions about the accuracy of TEOM during measurements of the (semi-)volatile aerosol. The development of the humidity and temperature-controlled installation in combination with a designed weighing protocol improved the accuracy of weighing of collected aerosol samples. Tests on the SJAC have been performed in order to study its operation when measuring the heavy metals and organic compounds. The results indicate that the SJAC can be used for sampling in an urban environment as its collection efficiency is virtually 100% at high number concentrations and does not depend on the water-solubility of the aerosol. The limit of detection of the SJAC can be reduced by insulation and applying higher flow rates. The emissions of road traffic in a tunnel have a significantly larger proportion of nanometer-sized particles than when directly measured at the outlet. This suggests the production of new particles in ambient air by homogeneous nucleation. The experiment with the moving van demonstrates that the variation in particulate matter in and near streets can be attributed to prevailing traffic densities; for example, higher number concentrations are measured at streets with densely packed through traffic as compared to the numbers found in quiet residential areas. The aerosol number concentration is mostly due to the urban traffic; this is especially apparent when air has first traversed over a city when low background levels occur. These experiments, performed in the Drecht tunnel, Nijmegen, Amsterdam and Petten (all in the Netherlands), substantiate that aerosol number concentration may be a better indicator than mass concentration for adverse effects on health observed in cities. More knowledge on the emissions of the ultrafine particles is necessary to describe the dynamics in the aerosol concentrations (number and composition). If this knowledge is acquired, relations with health indicators can be assessed more accurately and the design of an effective abatement strategy comes within reach. 18 refs.

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