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20 November 2009
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Particulate matter (PM) is defined in many ways but is essentially
particles that are floating or are suspended in the atmosphere. They are
categorised according to the effective maximum particle size in
micrometres as follows:
| PM10 |
These are large particles that will often settle out or be
washed out by rain. If breathed in, they will mostly be trapped in
the nose and throat and few will reach the lungs |
| PM2.5 |
These are smaller particles which have a longer lifetime. They
will reach the lungs and can cause cumulative alveolar damage. |
| PM1.0 |
These are still smaller and will readily reach the lungs. |
| PM0.1 |
These are classed as nanoparticles. There is research being
conducted on nanoparticles which are known to pass into the blood
stream and, from there, through body membranes into organs. |
The great majority of particles is classified as coarse, between 10 and
2.5 µm. Fine particles are in the PM2.5 and PM1.0 categories, while the
PM0.1 category is ultrafine.
The effect of particles on human tissue depends on their physical and
chemical characteristics. Sharp-edged particles, such as silica, can cut
lung tissue, causing such diseases as pneumosilicosis and
pneumoconiosis. The needle-shaped particles of some grades of asbestos
can cause mesothelioma and asbestosis. Chemically neutral rounded
particles would be less dangerous. Most organic particles, such as from
cigarette smoke, diesel exhausts etc. may bbe potentially dangerous,
causing emphysema, asthma, arteriosclerosis, lowered immunity and
cancer.
Particles may come from many different sources, the great majority
being natural, if averaged over the earth's surface. These include
volcanoes, forest fires, wind-blown desert dust, sea salt, desquamated
particles from living organisms (including human skin), pollen etc. As a
general rule, these have little effect on human health (exception:
allergic reactions), provided they are not present in excessive
quantities. On the other hand, some of the man-made particles can be
very harmful, even in small quantities, such as those resulting
from unfiltered diesel exhausts, tyre and road bitumen particles, smog
particles resulting from the photochemical reactions between volatile
organic compounds and nitrogen oxides, power station stacks, domestic
chimneys, heavy metal compounds etc. The chemicals in these pollutants
often have a cumulative effect; for example, it is known that mercury
compounds will slowly cause lesions of the central nervous system,
especially in children.
The recommended maximum particulate matter PM10 concentration recommended
by some bodies is 50 µg/m3 with a
2005 EU limit of 40 µg/m3 and a proposed 20 µg/m3 for 2010.
These are annual mean values, with a number of daily events exceeding
these values permitted.
So what is the situation in Cyprus? There is little to rejoice about.
Cyprus has some of the dustiest cities in the European Union. Before
going into the details, let me mention the khamsin episodes.
The khamsin is a dust storm in N. African and W.
Arabian countries. The word comes from the Arabic word for 50 because it
is supposed to occur over 50 days from mid-February. It raises enormous
quantities of sand or dust, including PM10. On occasion, it blows over
Cyprus, as in this 26 February 2006 satellite view of the island. On
this occasion, the PM10 value peaked at over 3000 µg/m3
in a number of localities. On an average, we get 2 - 3 such
episodes per year.
In rural areas of Cyprus, the Sahara dust is
responsible for about half the PM10 levels exceeding 50 µg/m3
but this is not the case in the cities. In central Nicosia (at the old
General Hospital), 60% of the excesses are traffic related, 17% are
caused by sea salt and local soil dust. Similar figures have been
recorded in other cities. It is therefore erroneous to impute Saharan
dust under urban conditions.
As can be seen from the above chart, Cyprus does not compare well with many
cities in Europe, and this is largely imputed to traffic. The situation may have
improved slightly since 2002/3, as many of the older diesels have been scrapped,
but there are still too many badly maintained vehicles. In addition, there has
been a notable increase of gas-guzzling luxury vehicles and large SUVs in the
last couple of years; although these are cleaner, the majority are still diesels
which are not fitted with particle filters. In any case, such filters are less
effective for the smaller particles, which are the most dangerous; they are most
effective for PM10.
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