DEADLY FILTH
DO LOWER SPEED LIMITS ON MOTORWAYS
REALLY CUT SMOG?
Unbearably polluted cities… Smog levels well over permitted limits… Almost
every week there seems to be a news story related to the problem of particulate
matter. Health studies show that its impact should not to be underestimated.
But is there anything we can actually do?
A NASTY MATTER
***
WHAT IS PARTICULATE MATTER?
Essentially, particulate matter (PM) is fine dust in the atmosphere. But that simple description
covers a multitude of substances. So we subdivide PM according to the size of its particles.
PM10, for example, refers to all particles with a diameter of less than 10 micrometres. By
comparison, the thickness of a human hair is 50 micrometres.
In the Netherlands, more than half of all PM (55%) comes from natural sources, with sea salt being the
main component. This is due to the country’s geographical position, next to the North Sea. Other
major “natural” forms of PM are pollen and plant residues. Volcanic eruptions also make a substantial
contribution. The high concentrations of ash produced by the Eyjafjallajökul volcano in Iceland in 2010
grounded aircraft across much of Europe for several days.
45% of the PM in the Netherlands is generated by human activity, including industry and road traffic.
The amount produced by New Year fireworks should not be underestimated either. Fortunately, that is
just once a year…
***
In July 2012 the Dutch Minister of Infrastructure and the Environment, Melanie Schultz van Haegen,
increased the speed limit on a number of stretches of urban motorway from 80 to 100 kilometres per
hour. The roads affected included the A13 at Overschie (Rotterdam), and the A10 in the western part
of Amsterdam. The increase was quickly reversed, however, after Friends of the Earth Netherlands
secured an injunction against it. Why? PM levels in excess of statutory limits, posing a danger to
public health. But was that a correct decision? Is there any scientific evidence that local measures like
lower speed limits really do cut levels of dangerous substances in the atmosphere?
THE LESS THE BETTER
The detrimental health effects of PM have long been known. They are why the Dutch government has
taken drastic action to cut emissions. Like other European countries, it is actively encouraging
businesses to develop cleaner, more sustainable technology. Although this has been the trend for
some years now, we are not there yet. Recent research shows that even the permitted levels of PM
pose a threat to public health. The best policy will always be: the less the better.
NOT ONLY THE WEAK
The World Health Organisation (WHO) recently declared that reducing air pollution is one of the most
important ways to improve public health. In fact, it classifies polluted air as “carcinogenic”.
But how many of us are really aware of the dangers of PM? Do you often stop to think about it?
Probably not. After all, it almost certainly has no direct effect on your everyday life. Only on a few very
hot days each year does the National Institute for Public Health and the Environment (RIVM) issue
specific air pollution warnings for the Netherlands.
“IN THE LONG TERM, PM IS
A DANGER TO US ALL”
Even then, such alerts are usually aimed at vulnerable groups like the elderly, people with
cardiovascular diseases and asthma patients. Serious immediate consequences are confined to a
relatively small section of the population. In the long term, however, PM affects us all. Even the
healthy are at risk of falling prey to the diseases it causes.
***
THE GREAT SMOG OF ’52
Air pollution is probably as old as mankind. Roasting meat over an open wood fire and
heating homes with coal remain major sources. But the problem really began to take on
serious proportions with the construction of the large coal-fired steam engines and
polluting factories. One of the best examples of their impact is the Great Smog in
London.
The British capital had struggled with a winter smog problem ever since the Industrial
Revolution. But what happened in December 1952 was unprecedented. It was an extremely
cold winter. In their efforts to keep warm, Londoners had to burn thousands of tons of coal.
The resulting smoke mixed with natural fog to produce choking smog, which lingered over the
city in the calm, almost windless weather. Normal life ground to a standstill. Flights at
Heathrow Airport were cancelled, and road and rail traffic halted by poor visibility.
Eyewitnesses reported that in places they could see no more than 10 metres in front of their
faces. The smog hung over the city for more than five days before the wind finally picked up
and dispersed it. The human consequences were tragic. Over the next three months, an extra
6000 deaths were reported – mainly among the very young and the elderly. The main cause of
death was oxygen deprivation, exacerbated by existing respiratory problems. Long-term
estimates put the total death toll attributable to the Great Smog at about 12,000.
***
A COMPLEX PROBLEM
The distribution of PM is a complex problem. It is known that particulates can travel thousands of
kilometres in the upper atmosphere. In the Netherlands, for example, parked cars are occasionally
dusted with a layer of fine red or yellow sand originating in the Sahara desert. Sources closer to home,
such as the heavy industries of the Ruhr valley in Germany, also make a substantial contribution to
Dutch smog. High-altitude clouds of PM can be monitored by satellite, but measurement becomes
more problematic once downdraughts start pushing it towards the ground. At the local level,
researchers still know relatively little about how particulates spread. To address this issue, scientists at
Delft University of Technology have launched a project looking at how airflows in and around built-up
areas affect the dispersion of PM.
DELFT RESEARCH
The research has already revealed that the way PM spreads locally is very much dependent upon the
topography of an area. For example, the height of the buildings and the width of the streets separating
them are largely responsible for determining whether exhaust fumes tend to linger or are easily blown
away by the wind. Another important factor is the ambient temperature: dispersion patterns are
completely different on warm summer days and cold winter ones.
The Delft project is homing in on one particular and common situation: the urban motorway. In cities,
with their heavy traffic, emissions of pollutants are high and more and more people are living close to
their source.
“AIRFLOWS MAKE IT HARD
TO PREDICT WHERE PM
WILL GO”
HARD TO PREDICT
Another project focus is predicting peak concentrations in disaster situations. “The current models
allow us to forecast long-term averages very well,” explains researcher Jasper Tomas. “But in the
event of a chemical disaster like the one in Moerdijk (in January 2011), we want to know immediately
whether and where peak concentrations of toxic substances are likely to occur. If evacuations are
going to be needed because the limits are exceeded, local governments and environmental
organisations want to know that straight away.”
Since the government is required by law to guarantee good air quality, it is important to know what
dispersion models to use when, say, building a new residential development. Applying different
models to the same standard scenario usually produces a wide variety of results, so which is the most
reliable?
Local PM dispersion is hard to predict. This is due primarily to the airflows around buildings and roads.
In urban environments, these are almost always turbulent. And turbulence is a challenging
phenomenon for scientists. At first sight it looks like a complete chaos of apparently random and
unpredictable swirls of air. How PM is dispersed in this tumult would seem to be anybody’s guess. But
research has shown that there are in fact consistent and universal structures in turbulence, even in
built-up areas. The Delft researchers thus believe that understanding complex turbulence is essential
to the development of accurate dispersion models. Their work has now reached the stage where they
can take specific measurements of both airflows and PM concentrations.
“WE WANT TO CREATE
CLEAN CITIES WHERE PEOPLE
CAN LIVE HEALTHILY”
What makes the Delft project so innovative is that it can measure and calculate dispersion around a
building, even when the PM itself comes from a source elsewhere in the city. Moreover, this kind of
simulation model can make it possible to examine how temperature affects dispersion. Especially in
cities, where heating and cooling patterns are quite different from those over open ground,
temperature-related mixing effects are an important factor with an evident, observable impact on local
dispersion. In short, warm weather spreads PM more widely than cold weather. The relationship
between temperature, source and airflow thus provides valuable insights into PM dispersion. “It is the
link between fundamental flow theory and its practical application to improve air quality which makes
this research so interesting,” project leader Gerrit Elsinga explains. “Our ultimate goal is to create
clean cities where people can live healthily.” And in so doing, perhaps it will help determine whether
specific measures like reducing speed limits on urban motorways really can reduce local levels of
harmful substances. So far, however, that is not entirely certain.
PM: THE DANGERS
Health studies indicate a clear link between air pollution and certain diseases.
Immediate symptoms include irritation of the eyes, nose and throat. People with
asthma or bronchitis often suffer more respiratory problems, too. And the list of longterm effects is truly staggering: heart failure, lung cancer, impaired brain development
in premature babies, and so on.
Particulate matter enters the body through the nose and mouth and penetrates all the way to
the lungs. Some is filtered out by the mucous membranes, but many of the smaller particles,
especially, reach the alveoli – where the lungs transfer oxygen to the blood – unhindered.
From there they spread throughout the body.
Based upon long-term studies and other data, the WHO has calculated that each year no
fewer than seven million people worldwide die as a result of air pollution. Of them, between
1,700 and 3,000 are Dutch. Although the Netherlands possesses relatively clean technologies,
it is still one of Europe’s most polluting countries. That is due primarily to its combination of a
high population density and high energy consumption.
AIR POLLUTION AND AUTISM
Scientists have discovered that autism is up to three times as common in residential areas with
polluted air as in those with clean air.
This finding was reported by Dutch daily newspaper De Volkskrant at the end of last year, citing a
study by the University of Southern California. For both particulate matter and nitrogen dioxide, the
rule seems to be: the greater the concentration, the higher the risk of children developing autism.
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