Sahara dust, sea spray and fires contribute to bad air quality - 11 July, 2012.
Human activities are the main cause of poor air quality, but natural sources of air pollution also play a role. A new report from the European Environment Agency (EEA) considers how particulate matter from these natural sources affects the air we breathe.
The report is
the first evaluation of Member State reporting under the EU's Air Quality
Directive. The directive sets legally binding limit values to improve air
quality. However, countries can subtract the pollution from natural sources, as
they are only obliged to reduce man-made air pollutant emissions. So the report
also includes European Union (EU) Member States documentation of natural
contributions which led to exceedances of air quality limit values set by EU
legislation.
It is difficult to calculate the exact amount of
pollutants emitted from natural sources, the report notes, but in many
countries the contribution to particulate matter levels in the air can be
significant.
The most common natural sources of particulate
matter in Europe are desert dust, volcanoes, forest and grassland fires, and
salt from sea spray. The particular source of pollution can be identified using
various methods including chemical analysis of particles sampled from the air,
meteorological data satellite measurements and modelling.
Eleven EU Member States reported that natural sources
pushed particulate matter concentrations over the limit values in 2008 or 2009
(Austria, Cyprus, Germany, Greece, France, Italy, Latvia, Malta, Portugal,
Spain and the United Kingdom). The highest numbers of cases were reported by
Mediterranean countries (Cyprus, France, Greece, Italy and Spain). Spain had
the highest number of measuring stations reporting exceedances caused at least
in part by natural sources.
"Poor air quality from natural sources is by
definition outside of our control," EEA Executive Director Jacqueline
McGlade said. "But this analysis shows that authorities should make extra
efforts to reduce the air pollution they can control, because the cumulative
effect of natural and man-made particulates can damage people's health."
Natural
sources of particulate matter
- 'African dust' from the Sahara is the most
common natural source of particulate matter in the air. In the Western and
particularly in the Eastern Sahara rainfall is extremely rare and
irregular. Temperatures can rise above 50° C during the summer months.
Extremely dry and hot conditions create turbulence during the day which
can propel dust upwards to a height of 4-5km. Such turbulence is usually
followed by meteorological stability during the night. Particles can stay
at these heights for weeks or months, and are often blown across Europe.
- Sea spray is also a source of particulate
matter, and can contribute up to 80 % of particle levels in the air in
coastal areas. This is mostly salt, whipped into the air by strong winds.
- The sudden eruption of a volcano, for
example on Iceland or in the Mediterranean, has the potential to produce
transient peaks of airborne particulate matter in Europe.
- Forest and grassland fires in Europe burn an
average of almost 600 000 hectares of land per year, a significant source
of air pollution. It is difficult to determine whether these fires are
truly 'natural sources' – the report notes that approximately nine out of
10 fires are caused directly or indirectly by humans, for example by
arson, discarded cigarettes, campfires or farmers burning crop
residues after the harvest.
Source: www.eea.europa.eu
11 July, 2012.