Overview of Measuring Methods in the Network of Automated Monitoring Stations
SO2 concentration is measured by the ultraviolet fluorescence method, where the analysed
sample is exposed to UV-lamp irradiation with energetic excitation of SO2 molecule. With the
backward conversion of the molecule into the basic energetic level, energy as fluorescing
radiation is released. This radiation is proportional to the sulfur dioxide concentration and is
detected by a photomultiplier.
NOx concentration is measured by a chemiluminescence analyzer for the NO, NO2
and NOx concentration measurement. The principle of this method stands on the nitrogen molecule
excitation by ozone. With the conversion of the molecule into the basic energetic level,
liberation of radiation as chemiluminescence occurs. This radiation is detected by a
photomultiplier. The analyzer design makes possible the acquirement of information on nitrogen
monoxide (NO), nitrogen dioxide (NO2) and nitrogen oxides (NOx) concentrations.
For PM10 concentration (suspended particulate matter fraction up to 10μm particle
size) measurement the radiometric method is used. It stands on beta-ray absorption in a sample
captured on filtering material. The difference between the beta-ray absorption of the exposed and
non-exposed filtering material, which is proportional to the mass of the captured suspended
particle matter, gives the information on its concentration.
The automated stations installed by the State Health Institute and some stations of the Public
Health Service use for the suspended particulate matter continual monitoring the tapered element
oscillating microbalance (TEOM). It measures the mass of the sample captured on a replaceable
filter according to the oscillating tapered element frequency variation. The air sample passes
through a filter where the dust particles are captured and runs through a hollow tapered element
to a vacuum pump with an electronic flow control.
CO concentration is measured by the method of IR-correlation absorption spectrometry. The
radiation from an infra-red source passes through two parallel cells, one of which contains a
non-absorbing background gas, the other contains the analyzed flowing sample of ambient air. The
difference in energy between the sample and the reference cell is proportional to the carbon
monoxide concentration.
The ozone concentration measurement is based on ultraviolet absorption photometry,
resting upon absorption of radiation with the wavelenght of 254 nm by ozone in the analyzed
sample. The radiation source is an UV-lamp and clean air (zero) and the sample itself are
alternately measured in cells. The presented method with automatic pressure and temperature
compensation meets the challenging requirements for O3 measurement.
During the year 1997 continual measurement of aromatic hydrocarbons (benzene, toluene and
xylenes) by BTX analyzers and gas chromatography method was introduced at two AMS (Libuš, Most).
It is a case of standard linkage to a sampling probe in a container.
Overview of Measuring Methods in the Network of Manual Stations
The average daily sulfur dioxide concentrations are measured by the spectrophotometric
method using TCM and fuchsin (West-Gaeke method). The sulfur dioxide is absorbed into a sodium
tetrachloromercury solution (TCM) containing Chelaton III. The compound formed reacts with
fuchsin and formaldehyde in acid medium to yield a red-purple colour, which is measured
spectrophotometrically at 586 nm. The average daily concentration is determined by drawing an air
sample (1.2 to 2.4 m3 per 24 h) through two absorbers containing absorption solutions, placed in
series. The sampling apparatus consists of two capillary absorbers, a gas meter and a membrane
pump. The sample must be fed to the absorber through a teflon tube.
A spectrophotometric method using thorin is applied at selected stations with lower sulfur
dioxide pollution levels. The air is drawn through a filter to capture solid particles and then
through another filter impregnated with sodium hydroxide to determine sulfur dioxide. After
extraction from the filter, the sulphate ions are precipitated with barium perchlorate. Excess
barium ions are determined spectrophotometrically at 520 nm after reaction with thorin. The
sampling apparatus consists of a sampling head, membrane pump and dry gas meter. The volume of
air drawn through the apparatus is between 2.5 and 10 m3 per 24 hours.
At several Public Health Service´s stations the concentrations of sulfur dioxide and nitrogen
oxides are measured by continual-manual method of electrical fuel cell ( APM analyzer of City
Technology Corp.)
SO2 and NO2 concentrations are measured by the coulometric
method at some semiautomatic stations. That is an electrochemical method where electrolytical
current is proportional to gas concentration according to Faraday's law.
The average daily concentration of nitrogen oxides is measured by guajacol (i.e. modified
Jakobs - Hochheiser) spectrophotometrical method using NEDA and sulfanilamide. Nitrogen oxides
are sampled through an oxidation tube (NO present is oxidized to NO2). All the NO2 absorbed into
the solution of sodium hydroxide with addition of guajacol reacts in acid medium of H3PO4 with a
solution of sulfanilamide and N-(1-naphthyl)ethylene diamine dihydrochloride (NEDA) to form a red
colour. The intensity of the colour is measured spectrophotometrically at 560 nm. The sampling
apparatus consists of a teflon probe, which is connected to a tube filled with oxidation material
at the entrance to a set of two capillary absorbers connected in series. The apparatus is then
connected to a water gas meter and membrane pump.
The concentrations of NO3- and HNO3 are measured
spectrophotometrically using NEDA and sulfanilamide (Griess reaction). Nitrates are captured on
the teflon filter, gaseous HNO3 is captured on the filter impregnated with NaCl and then eluated
by NaOH, spectrophotometrical measurement is the same as in the case of nitrogen oxides.
The concentration of suspended particulate matter is determined by a gravimetric method.
The sample is taken through continuous filtration of outdoor air on selected filtering material
(membrane with a mean pore size of 0.85 μm, teflone with a mean pore size of 1 μm or glass fibre
with a capturing capacity more than 99.5 %) with a rate 33 - 55 cm.s-1. The filter head is turned
with the open side down, at a distance of 1.5 - 3.0 m above the surface. The sampling time and frequency
correspond to the character of the sampling site location. The amount of sample captured on the filter
(in μg) is determined gravimetrically as a difference between the weight of the filter prior to and after
the exposure.
The concentration of metals in the air is determined using membrane filters Synpor for sampling
followed by mineralization using hot nitric acid. In CHMI, the metals were analyzed by the atomic
absorption spectrophotometry (AAS) till 1996. This method is still used at the stations of the
Public Health Service and ORGREZ. In 1997 within the framework of Black Triangle the inductively
coupled plazma - mass spectrometry is applied, with high-volume sampling on glass-fibre filters.
The polarographic method is used at several stations of the Public Health Service.
The resultant atmospheric concentration of suspended particulate matter or metal in the air is
given in μg.m-3. The sampling apparatus consists of a sampling head, dry gas meter and at
pump.
The concentration of SO42- in SPM is measured by X-ray fluorescence (
XRF) method using paper filters Whatman 40 for sampling.
The concentrations of NH3 and NH4+ are measured
by Berthelot method. Ammonium ions are captured on the first located teflon filter, gaseous NH3
is captured on the filter impregnated with oxalic acid, NH4+ ions
eluated by demineralized water react with alkaline solution of phenol and NaClO.
Spectrophotometrical measurement at 630 nm is used.
Volatile organic compounds (VOCs) are determined by gas chromatography method using
separation on a capillary column with an air sample taken in special steel canisters at the
measuring site. Samples are taken on Monday and Thursday of each week at 12:00 UTC for a period
of 10 minutes. The sample is fed into the chromatograph from the transportation canister through
a preconcentration unit.
Persistent organic polutants (POPs) are captured on glass-fibre and polyurethan filters
using high-volume pump sampling. The sampling lasts 24 hours and starts every Wednesday at 7:00
UTC (CHMI - MS KoÅ¡etice). At Public Health Service´s stations the samples are taken every sixth
day also at 7:00 UTC. Exposed filters are eluated with dichlormethane. After purification and
preconcentration the selected POPs are measured by gas chromatography with mass detection.
At CHMI stations the precipitation is sampled using automatic sampling devices, which are
automatically opened during rain periods (wet-only sampling). Alternatively, wet-only samples are
taken manually at several stations by daily cumulation method. Sampling interval is one week
from 1996 - 97, exceptionally one month. Since 1997 special sampling for heavy metals was
introduced - weekly bulk. Devices constantly opened throughout the exposure period (bulk
sampling) are used at the stations of ČGÚ and VÚV T.G.M. with monthly sampling. Throughfall
samples are taken as cumulative bulk samples from nine regularly placed samplers at ČGÚ and CHMI
stations.
After completion of sampling, the precipitation samples are stored in the cold (3 - 5°C) and
dark. Sensitive analytical techniques are used for the analysis, e.g. atomic absorption
spectrophotometry for cations, ion chromatography for anions, spectrophotometry for NH4+,
ion-selective electrode for F- and measurement of the conductivity and pH value.
Overview of measuring methods of supplementary meteorological parameters
The wind direction and velocity are measured using weather cock and anemometer. Position
and turning velocity of the wind gauge are taken optoelectronically or transferred to electrical
voltage using circular potentiometer and tachodynamo.
Energy of solar radiation (GLRD) is measured in W.m-2 using temperature
difference method. The temperature difference of black and white coloured surface segments
with different reflection to short-wave solar radiation is measured.
