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This
discussion is focused on heavy metals in the atmosphere. However to fully
assess the environmental risk from these compounds, research
has also to be expanded in soil and
water. There are few available data for most of heavy metals in the atmosphere.
The main sources of arsenic, cadmium and nickel are the stationary industrial combustion processes, (such as
the iron and steel industry and the non-ferrous metal industry), transport and
other mobile machinery.
In the
northern Hemisphere, anthropogenic emissions have increased the background
concentrations of mercury in air by a
factor of 2-3 since before industrialisation. More than half of the
anthropogenic emissions are generated during the combustion of coal in utility,
industrial and residential boilers.
Atmospheric
mercury exists mainly in the form of elemental mercury vapour (Hg0)
(90 to 99%), particle bound mercury (< 5%) and gaseous divalent mercury (e.g.
HgCl2) (<5%). There is no standard
method in Europe for assessing the levels of mercury (and its
compounds) in ambient air and precipitation.
The
position papers which have been produced (see web link
section below) as a basis for the
development of an AQ directive on heavy metals, gives assessments of the HM in
air situation in Europe presently, and cover sources and risk assessments,
measurement methods and network considerations.
A CEN
standard is being developed on the measurement of As, Cd and Ni (CEN draft standard prEN
14902.
Briefly
about measurement methods
Arsenic, cadmium, nickel
Until
the upcoming CEN standard will be available, the Working Group of EC experts
recommends using a
provisional reference method. This method would include sampling for PM10
as described in CEN standard EN 12341, complete digestion, and atomic
absorption spectrometry for analysis. The Member States can use any other
method, which can be demonstrated to be equivalent.
Mercury
In the
atmosphere, the main three forms of Hg are: elemental Hg vapour (Hg0),
Reactive Gaseous Mercury (RGM) and Total Particulate Mercury (TPM). Of these
three forms, only Hg0 has been tentatively identified with
spectroscopic methods while the other two are operationally defined species,
i.e. their chemical and physical structure cannot be exactly identified by
experimental methods but are instead characterised by their properties and
capability to be collected by different sampling equipment.
Sampling
and analysis of atmospheric Hg is often made as TGM (Total Gaseous Mercury),
which is mainly composed of elemental Hg vapour with minor fractions of other
volatile species. In the last few years, new automated and manual methods have
been developed to measure TGM.
A major conclusion from researchers investigation on the available methods for Hg
was that ambient levels of TGM could be
measured with relatively high accuracy whereas TPM and especially RGM are more
complex.
Quality control of monitoring data
Annex VIII of the 1st and 3rd
Daughter Directives (see web links below) specifiy the
required accuracy of measurement data, as well as the minimum data capture
(parts of the year the measurement data must be available from a monitoring
station). These requirements are laid down as a guide to what quality-control
and –assurance (QA/QC) programmes that monitoring network operators need to
follow to comply with the quality objectives. QA/QC procedures are dealt with
in the Topic template How to secure the quality of the monitoring data? Quality assurance (QA) and Quality Control (QC) systems and procedures.. |