About
monitoring methods
The methods for
monitoring these pollutants have been developed and refined over many years.
There are several well-developed methods that can be used. For the gases SO2,
NO2 and ozone, the averaging times of the limit values (from an hour
to one calendar year) implies that, in general, automatic methods are needed,
which register the concentrations continually. The instruments have sensors
that provide concentration values every few seconds, which are treated
internally in the instrument to provide average values for an hour, or shorter
or longer periods.
Lead is contained
mainly in suspended particles, and methods deal only with the lead in
particulate matter. The limit value for lead prescribes only an averaging time
of one year. Methods for lead are based upon sampling of the air/particles
through filters, and subsequent analysis in a laboratory.
Available methods:
The “Position Papers”
worked out by EC Working Groups as a preparation for the Air Quality (AQ)
Directives contain useful sections summarising measurement and monitoring
methods, see the web links immediately below:
·
SO2:http://www.europa.eu.int/comm/environment/air/pdf/pp_so2.pdf
·
NO2: http://www.europa.eu.int/comm/environment/air/pdf/pp_no2.pdf
·
Ozone:http://www.europa.eu.int/comm/environment/air/documents/pos_paper.pdf
·
Lead: http://www.europa.eu.int/comm/environment/air/pdf/pp_pb.pdf
·
CO: http://www.europa.eu.int/comm/environment/air/pdf/pp_co.pdf
Reference methods
·
The following methods
are prescribed in the AQ Directives as reference methods for SO2, NO2,
ozone and lead measurements in Europe:
·
SO2: CEN EN
14212:2005 Ambient air quality - Standard method for the measurement of the
concentration of sulphur dioxide by ultraviolet fluorescence.
·
NO2: CEN EN
14211:2005 Ambient air quality - Standard method for the determination of the
concentration of nitrogen dioxide and nitrogen monoxide by chemiluminescence.
·
Ozone: CEN EN
14625:2005 Ambient air quality – Standard method for the determination of ozone
in ambient by means of ultraviolet photometric method.
·
CO: CEN EN 14626:2005
Ambient air quality – Standard method for the determination of CO in ambient
air by Non-dispersive Infra-Red method (NDIR).
·
Lead: Sampling1):
o
Before 2005/2010:
Filter method according to Directive 82/884/EEC
o
After 2005/2010:
Filter method as for PM10 sampling, according to EN 12341 standard.
o
Analysis: Atomic
absorption spectrometry method or ICP-MS method (CEN standard Draft prEN 14902, of October 2004).
The method of Directive
82/884/EEC applies to measurements to comply with this directive carried out
until 2005 (until 2010 for areas in the immediate vicinity of some specific industrial
sources). After this time, the method of the EN12341 standard applies (please
see Directives 82/884/EEC and 1999/30/EC for details).
Determination of
equivalence of other instruments and methods
The procedure for
determining whether a candidate method is equivalent to the reference method is
described in http://www.europa.eu.int/comm/environment/air/cafe/pdf/equivalence_report_final.pdf
Quality control of
monitoring data
Annex VIII of the 1st
and 3rd Daughter Directives (see web links below) specify 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 How to secure the quality of the monitoring data? Quality assurance (QA) and Quality Control (QC) systems and procedures..
Minimum number and
location of monitoring stations in a Member State, according to
the AQ Directives
Annex VII of the 1st
Daughter Directive (DD), for SO2, NO2 and lead, and the 3rd
DD, for ozone (see web links below), as well as Annex V of the 2nd
DD for CO, state the requirements to what type of areas (zones) should be
monitored, and the minimum number of sampling stations as a function of the
population in an agglomeration or zone. For NO2 and CO, in zones
where the upper assessment threshold is exceeded and there should be more than
1 station, there should be at least one urban background and one
traffic-oriented station.
The determination of
which zones shall have monitoring stations is generally done through the
activities of the “Preliminary Assessment” that the Member State shall carry
out, in accordance with the Directive on ambient air quality assessment and
management (the Framework Directive) (96/62/EC) (see web link below).
Location of sampling
points, and exposure related monitoring
Annex VI of the 1st
DD and the 3rd DD (for ozone), and Annex IV of the 2nd DD
(for CO) presents considerations that shall apply regarding the selection of
fixed point measurements. The annexes describe macroscale
setting and microscale setting considerations, both
for health- and ecosystems-protection related stations.
Stations directed at
human health protection should be located such that they provide data on areas
representing typical or maximum concentrations that the population in the area
is likely to be exposed to, directly or indirectly. This exposure should occur
for a period which is a significant part of the averaging period of the limit
value. Thus, it is prescribed that the monitoring should be exposure related.
This means simply that
stations directed for health protection should be located where people are
living or frequenting, and that the period during which they are likely to be
exposed in that area is comparable to the averaging time of the limit value.
For SO2, NO2, CO and ozone, the averaging times of the
limit values are either 1 hour, 8 hours (ozone and
CO), 24 hours (SO2), or one calendar year (for SO2 and NO2).
So, monitoring stations for SO2, NO2, CO and ozone should
be positioned either in residential areas where people are potentially exposed
throughout the whole year or indeed during any 1/8/24-hour period, or they
should be in “hot-spot” areas where people are likely to be exposed over a
significant part of any 1/8/24-hour period. For NO2 and CO, this
could be residences very close to roads with high traffic, while for SO2
it could be in areas close to industrial sources with large SO2
emissions. For ozone, potential hot-spots are in residential areas downwind of
large urban areas where photochemical reactions are likely to occur, while ozone
concentrations are likely to be low in areas close to local emissions from
traffic sources.
Areas/locations where
people or ecosystems are not likely to be exposed over a significant part of a
limit value averaging period should NOT be considered for monitoring.
For lead where only annual average
exposure applies, only residential areas should be considered for monitoring.
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