AUTOMATED MONITORING STATIONS   MANUAL STATIONS   SUPPLEMENTARY METEOROLOGICAL PARAMETERS  

Overview of Measuring Methods in the Network of Automated Monitoring Stations (AMS)

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.

The concentration of nitrogen oxides 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, release 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 10ľm 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 National 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 filters, 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 stations the concentrations of sulfur dioxide and nitrogen oxides are measured by semiautomatic method of electrochemical fuel cell ( APM analyzer of City Technology Corp. with a selective micro-fuel cell).

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.

At CHMI stations and stations of EKOTOXA private company 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). At some stations At some stations only NO2 is measured; the oxidation tube is lacking. 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. At Public Health Service stations the average daily concetrations of nitrogen oxides are measured bu similar spectrophotometric thiethanolamine method. After oxidation NO2 is absorbed into the solution of thiethalomine with sulfanic acid in acid medium of H3PO4 using NEDA.

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 ambient air on selected filtering material (membrane with a mean pore size of 0.85 ľm, teflone with a mean pore size of 1 ľm 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 is then same at all CHMI stations - 24 hours. The sampling frequencies correspond to the character of the sampling site location. The amount of sample captured on the filter (in ľg) is determined gravimetrically as a difference between the weight of the filter prior to and after the exposure.

In CHMI, the concentration of metals in the air was analyzed by the atomic absorption spectrometry (AAS) till 1996 using membrane filters Synpor for sampling folowed by mineralization using hot nitric acid. This method id still used at the station of the Public Health Service and ORGREZ. Since 1998 the AAS method is still used in CHMI only for the determination of cadminum concentration at selected stations. The filters are mineralized using hot nitric acid and hydrogen peroxide in microwave apparaturs MLS 1200 MEGA.

At several Public Health Service stations then polarographic method and indutively coupled plasma - atomic emission spectrometry (ICP-AES) are also used for the analysis of heavy metals.
Since 1997 the CHMI stations have determined the concetration of heavy metals in air also by a non destructive method of X-ray fluorescence (XRF) using a teflon filter. Within the framework of "Black Triangle" the inductively coupled plasma - mass spectrometry (ICP-MS) is applied, with high-volume sampling on glass-fibre filters.

The resultant atmospheric concentration of SPM and metal in the air are given in ľg.m-3 and ng.m-3 respectively. The sampling apparatus consists of a sampling head, a dry gas meter and a pump.

The concentration of SO42- in aerosl is measured by X-ray fluorescence (XRF) method using teflon filters (Gelman Laboratory RP2LO47) with a pore size of 1 ľg for sampling together with sampling for heavy metals.

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 Košetice). 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 and HBÚ AV ČR 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 spectrometry for cations (metals), spectrophotometry for NH4+, ion-selective electrode for F- in some cases and current 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 of the weather cock is taken optoelectronically or transferred to electrical voltage using circular potentiometer. The turning of the sensor of the anemometer is measured otoelectronicaly or transfered to electrical voltage using a 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.