7.2.1 Introduction
Measurement of gases and aerosols carried out in the subprogramme AC gives information needed for assessing the input of air pollutants to the ecosystem due to long-range transport in the atmosphere. Gases and aerosols may interact with trees and vegetation via dry deposition either by direct interaction in the canopy or indirectly via interaction of the deposited pollutants in soils and surface waters.
Air pollution concentrations can be compared to critical levels of pollutants of noxious gases and aerosol particles in order to assess the risk of direct effects of these pollutants to the flora. In addition, from the air concentrations it may be possible to indirectly estimate the dry deposition. This is especially important for pollutants that are subject to up-take or leaching by the canopy, like nitrogen compounds, where througfall measurements are subject to large uncertainties.
Data from neighbouring monitoring stations meeting the set criteria (e.g. EMEP sites) may be used for ICP IM purpose, provided that they can be proved by the data originator to be representative for the IM site.
Monitoring programme includes the following parameters:
Mandatory parameters
sulphur dioxide
nitrogen dioxide
ozone
particulate sulphate
the sum of nitrates in aerosols and gaseous nitric acid
∑(NO3- (part.) + HNO3 (gas))
the sum of gaseous ammonia and ammonium in aerosols
∑(NH3 (gas) + NH4+ (part.))
Optional parameters
carbon dioxide
As an indicator of climate change and as an additional stress factor to the ecosystem, carbon dioxide should be included into the monitoring programme on a voluntary basis.
Measurements of heavy metals in aerosols are recommended to be performed in the IM programme on a voluntary basis.
EMEP programme has included recommendations for sampling of heavy metals in particles (EMEP, web-manual, Chapter 3.11) and sampling of mercury in precipitation and air (EMEP web-manual. Chapter 3.12).
It is strongly recommended that the participants of the ICP IM programme follow the recommended methods as described below. If methods other than recommended in this manual are used, their comparability to the recommended method should be proved by the data originators.
7.2.2 Methods
Siting of collectors
Besides the general siting criteria given in Chapter 5, the special siting criteria as described by EMEP, Chapter 2.2 should be followed. In order to monitor long-range transboundary air pollution, the AC site must be representative with respect to exposure to the air mass, i. e. deep valleys, mountain tops and passes should be avoided. The ideal is a freely exposed site in moderately undulating terrain. The air inlet should be 2 - 5 m above ground.
To avoid vegetation influencing the ambient air concentrations, the AC site should not be sheltered by vegetation, but located in a large open glade or a large clearing. If, in highly forested IM sites, no suitable location can be found, the AC station may also be located outside the proper IM site (preferably in the direct neighbourhood) or even on a platform above forest canopy. Data from neighbouring monitoring stations meeting the above mentioned criteria (e.g. EMEP sites) may be used for ICP IM purposes, provided that they can be shown to be also representative for the IM site.
Sampling frequency
The requested measurement periods (frequencies) are 24 h (daily) up to 1 week (weekly) for all components besides ozone. Ozone is to be monitored continuously with 1 hour average values to be stored.
7.2.2.1 Sulphur dioxide
The most commonly used methods for sulphur dioxide measurements in EMEP today are the alkaline impregnated filter method and the hydrogen peroxide absorbing solution method (EMEP, Chapter 3.2.1). The recommended method for IM stations is the alkaline impregnated filter method, in combination with ion chromatography. At sites with annual average concentrations above 10 µgS/m3, the absorbing solution method can still be accepted. The recommended method is described in the EMEP manual (see references below) :
Principle : EMEP, Chapter 3.2.2
Interference : EMEP, Chapter 3.2.3
Sampling equipment / sample handling : EMEP, Chapter 3.2.4
Sample treatment : EMEP, Chapter 3.6
Chemical analysis : EMEP, Chapter 4.1
Calculation of results : EMEP, Chapter 3.2.4.4
7.2.2.2 Particulate sulphate
The recommended method for measurements of particulate sulphate at IM sites is the filter method in combination with ion chromatography (EMEP, Chapter 3.2.1). The aerosol filter can be mounted in front of the alkaline impregnated filter used for SO2 measurements in a filter pack. The recommended method is described in the EMEP manual (see references below) :
Principle : EMEP, Chapter 3.2.2
Interference : EMEP, Chapter 3.2.3
Sampling equipment / sample handling : EMEP, Chapter 3.2.4
Sample treatment : EMEP, Chapter 3.6
Chemical analysis : EMEP, Chapter 4.1
Calculation of results : EMEP,Chapter 3.2.4.4
7.2.2.3 Nitrogen dioxide
The recommended method for measurements of nitrogen dioxide at IM sites is a manual method based on the absorption of NO2 on a sodium iodide impregnated glass-sinter (EMEP, Chapter 3.3) followed by spectrophotometrical determination of the formed nitrite, either manually or automatically (flow injection analysis, continuous flow method). The recommended method is described in the EMEP manual (see references below) :
Principle : EMEP, Chapter 3.3.1.2
Interference : EMEP, Chapter 3.3.1.3
Sampling equipment / sample handling : EMEP, Chapter 3.3.1.4
Sample treatment : EMEP, Chapter 3.3.1.7-3.3.1.9
Chemical analysis : EMEP, Chapter 4.11
Calculation of results : EMEP, Chapter 3.3.1.10
7.2.2.4 Sum of nitrates in aerosols and gaseous nitric acid
The recommended method for measurements of the sum of nitrates in aerosols and gaseous nitric acid ∑(NO3- (part.) + HNO3 (gas)) at IM sites is the filter pack method, a combination of an aerosol filter and an alkaline impregnated filter (EMEP, Chapter 3.4.2), followed by analysis with ion chromatography. The recommended method is described in the EMEP manual (see references below):
Principle : EMEP, Chapter 3.4.2.2
Interference : EMEP, Chapter 3.4.1
Sampling equipment / sample handling EMEP, Chapter 3.4.2.6
Sample treatment : EMEP, Chapter 3.4.2.6
Chemical analysis : EMEP, Chapter 4.1
Calculation of results : EMEP, Chapter 3.4.2.7
7.2.2.5 Sum of gaseous ammonia and ammonium in aerosols
The recommended method for measurements of the sum of gaseous ammonia and ammonium in aerosols ∑(NH3 (gas) + NH4+ (part.)) at IM sites is the filter pack method, a combination of an aerosol filter and an acid-impregnated filter (EMEP, Chapter 3.4.3), followed by analysis with ion chromatography. The recommended method is described in the EMEP manual (see references below):
Principle : EMEP, Chapter 3.4.3.1
Interference : EMEP, Chapter 3.4.1
Sampling equipment / sample handling EMEP, Chapter 3.4.3.2
Sample treatment : EMEP, Chapter 3.4.3.5
Chemical analysis : EMEP, Chapter 4.1
Calculation of results : EMEP, Chapter 3.4.3.6
7.2.2.6 Ozone
The UV-absorption method using a continuous ambient air ozone analyser has been proven to be reliable and robust in field operation (EMEP, Chapter 3.9.1) and is therefore recommended for ozone measurements at IM sites. The recommended method is described in the EMEP manual (see references below) :
Principle : EMEP, Chapter 3.9.3
Measuring equipment and handling : EMEP, Chapter 3.9.4. and 3.9.5 Calibration : EMEP, Chapter 3.9.5.2 and 3.9.5.3
Even though only monthly values (calculated from 1 hour average values) are to be reported to the IM programme centre, 1 hour average values are to be stored by the data originator and to be made available on request. In addition, the accumulated ozone exposure over a concentration of 40 ppb (AOT40) is to be calculated from the continuous measurements (ppbhours) and reported to the IM programme centre. The AOT40 values should be calculated for the day light hours (between 8 am and 8 pm) separately for each of the months April-September (using 1 hour average values).
The procedure for calculating AOT40 values is described in the manual of the UN/ECE-Mapping Programme (see reference below):
Calculation of results (AOT40) : UN/ECE-Mapping Programme, Chapter3.2.4
7.2.2.7 Carbon dioxide
Measurements of carbon dioxide are not included in EMEP, but are recommended to be performed in the IM programme on a voluntary basis. In the WMO programme GAW non-dispersive infra-red (NDIR) gas analysers have been widely used to measure CO2 concentrations (WMO/TD-No.553). The NDIR method using a continuous ambient air CO2 analyser is also recommended for CO2 measurements at IM sites.
The recommended method is described in the WMO GAW guide (see references below) :
Principle : WMO, Chapter 2.1.1
Measuring equipment and handling : WMO, Chapter 2.1.1
Calibration : WMO, Chapter 2.1.1
Alternative methods:
A simple method for the determination of SO2, NO2, NH3 and O3 is the so called Passive flux sampling. The sampler consist of a impregnated filter where the absorption of the respective gases is a function of the ambient concentration. The method has proven to give comparable results with active sampling as described by the EMEP manual, and may be beneficial at sites without electrical power supply. Passive flux sampling may also be applied to examine horizontal or vertical gradients e.g. in the study of representativity of neighbouring monitoring sites. For a detailed description of the method it is referred to e.g. Ferm and Rohde, 1997.
7.2.3 Quality assurance / Quality control
It is very important to have a good quality of data, both being consistent in time (in order to assess trends) and space (for the comparisons between different sites and countries). The general procedures for quality assurance given by EMEP, Chapter 3.1.8 and in Chapter 8 of this manual should be followed. The QA/QC procedures should include all parts of the activities performed at the site, and in the laboratory.
Standard operation procedures should be followed for all activities. Necessary equipment, cleaning materials, sufficient supply of spare parts, etc. must be available. All operators should be well trained, sites and equipment must be inspected/controlled at least once a year by the quality assurance manager/data originator. The QA/QC routines in field also include field blanks and control samples, and sample transportation.
It is recommended that the chemical laboratory is accredited under one of the laboratory accreditation systems, or is performing close to these standards, e.g. EN 45001 and ISO/IEC guide 25. The laboratory must check on its performance, with respect to detection limits, precision and repeatability, by repeated analysis of control solutions etc.
It is strongly recommended to participate annually in international intercomparisons for all analysed compounds. It is also recommended to participate in field intercomparisons. The IM programme centre will be able to give information about relevant intercalibrations. All data should be verified and validated following the instructions given by EMEP, Chapter 5 and 6.
7.2.4 Data reporting
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Mandatory parameters
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list
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unit
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SO2S
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DB
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sulphur dioxide as sulphur
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µg/m3
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NDON
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DB
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nitrogen dioxide as nitrogen
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µg/m3
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O3
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DB
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ozone
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µg/m3
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AOT40
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IM
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Accumulated exposure Over a
Treshold of 40 ppb
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ppb*h
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SO4S
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DB
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sulphate as sulphur (particulate,
medium = PARTICLE)
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µg/m3
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NO3N_T
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IM
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sum of nitrates in aerosols and gaseous nitric acid ∑(NO3- (part.) + HNO3 (gas))
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µg/m3
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NH4N_T
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IM
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sum of gaseous ammonia and ammonium in aerosols
∑(NH3 (gas) + NH 4+(part.))
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µg/m3
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Optional parameters:
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list
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unit
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CO2
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DB
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carbon dioxide
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mg/m3
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Example files
AC example Excel file
AC example ASCII file
- File identifier SUBPROG states the subprogramme.
- MEDIUM refers to the analysed fraction, i.e. gaseous compound (GAS) or particulate compound (PARTICLE). Combined media are referred to as GASPART.
- LEVEL is given as the distance of the measuring equipment from the ground (cm).
- Spatial pool SPOOL gives the number of recording devices used for each parameter.
- For most parameters average monthly values are reported, status flag is X.
- General information on flags is given in Chapter 4.
- Sampling year and month are given as YYYYMM.
7.2.5 References
Berg, T., Hjellbrekke, A.G. and Skjelmoen, J.E. , 1996. Heavy metals and POPs within the ECE region.EMEP/CCC-Report 8/96. Kjeller, Norwegian Institute for Air Research.
EMEP web-manual: EMEP manual for sampling and analysis
http://www.nilu.no/projects/ccc/manual/
EMEP manual for sampling and chemical analysis, EMEP/CCC-Report 1/95, NILU, Kjeller, Norway, March 1996.
Ferm, M. and Rohde, H., 1997. Measurements of air concentrations of SO2, NO2 and NH3 at rural and remote sites in Asia. J. Atmos. Chem. 27, 17-29.
UN/ECE-Mapping Programme. Manual on methodologies and criteria for mapping critical levels / loads. Umweltbundesamt Texte 71/96, Federal Environmental Agency, Berlin, Germany, September 1995.
WMO Global atmospheric watch guide, WMO / TD-NO. 553 World Meteorological Organization, 1993.