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Title:
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Characterisation of particulate matter in urban air: instrumentation development and experimental results
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Author(s):
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Published by:
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Publication date:
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ECN
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1-4-2000
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ECN report number:
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Document type:
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ECN-R--00-001
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Other
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Number of pages:
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Full text:
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47
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Download PDF
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Abstract:
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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