ISO 9225:2012 pdf download – Corrosion of metals and alloys一 Corrosivity of atmospheres一 Measurement of environmental parameters affecting corrosivity of atmospheres.
5.2 Placement of measurement equipment
5.2.1 Continuous gas concentration measurement instruments
The instrument shall be located in a place that is sheltered from the rain arid protected from unauthorized people. Preferably, the instrument should be placed indoors with a tube leading out to the ambient air. Polyethylene or PTFE tubing is recommended and the length of the tubing should not exceed 2 m. The inlet shall be lacing down with a wider hood at the inlet to reduce the risk of sucking particulates into the tube.
5.2.2 Measurement Instruments with actlv. sampler
The active sampler equipment shall be placed according to the same rules as the continuous gas-rneasunng
5.2.3 Measurement instruments with diffusive sampler
The sampling device shall be placed with the open end facing downward under appropriate shelter. The air flow influences the gas diffusn in the sampler.
5.2.4 Deposition rate equipment
The equipment shall be sheltered from setting particles and from washing out by rain for outdoor deposition
measurements. The air flow influences the deposition rate.
5.3 Measurement methods and duration
5.3.1 Continuous measurement
The measurements shall preferably be carried out for one year In order to record the seasonal variation of the gas pollutants. The data from continuous measunng instruments shall be recorded as monthly average values. For the corrosivity estimation, the data shall be expressed as yearly mean values.
Standard instruments have detection limits in a range from 4 x 10 volume fractions to 1 x 106 volume fractions.
5.3.2 Measurement with active sampler
The methods are based on pumping air through an absorption unit with a reactive surface or liquid, with subsequent laboratory analysis of the amount absorbed The sampling period shall be one week, The data shall be collected over the sampling periods and summarized to monthly average values. The result Is given as an average concentration for the measuring period.
The measuring period is preferably one year or at least one month for each season of the year. For the corrosivity estimation, the data shall be expressed as yearly mean values,
NOTE The detection limits for air concentrations depend on the sensitivity of the analysing ins*ruments and the duration of the samplwig. For an analytical instrument with normal sensitivity. it is possible to obtain weekly average values with a detection hmil better than 0.1 pgi’n?.
5.3.3 Measurement with dIffusive sampler
Mean gas concentrations can be calculated using diffusive sampling devices. The principle used for diffusive sampling is shown in FIgure 1. The recommended sampling period Is one month, but can be extended to three months, corresponding to one measurement for each season of the year. The measurement period is preferably one year.
NOTE Normal sensitivity for weekly mean vetues Is down to 0.1 pgImfor SO2. but twgh& for other gases. Generaly the detection limit decreases utth increasing sampling time.
The general calculation model is specified in ISO 11844-3.
The data shall be expressed as yearly mean values.
5.3.4 Measurement of deposition rate of pollution
The deposition takes place on an absorbing or collecting surface similar to the surfaces used for diffusive sampling devices. In the deposition method standardized for SO2 deposition measurements, the gas reacts when it reaches the lead dioxide surface or alkaline surface (see Annexes A. B and C). In the methods standardized for airborne salinity measurements. particles (aerosol) are deposited on a wet or dry surface designed to collect this pollutant (see Annexes 0 and E). Since the collecting system is open, the deposition rate depends on the movement of the air.
NOTE The use of lead compounds can be restricted in some countries,
SO2 deposition measurements performed by the lead dioxide plates and by the lead dioxide cylinder differ with regard to the kind and shape of the deposition surface. Both measurements give values with low correlation for monthly sampling periods due to the greater variation in weather charactenstics. A high correlation exists for annual average values (see Annex F). Capture of sulfunc acid aerosols and sulfur-beanng species from precipitation and sea salt deposition can occur.
The SO2 deposition values used for the derivation of the dose4esponse functions given in ISO 9223 are either based on deposition measurements on alkaline surfaces or converted values based on concentration measurements,
Chloride deposition rates determined by the dry plate method and by the wet candle method differ because the kind and shape of deposition surface are different (wet/dry surfaces, cylindncatlplate format of the deposition surface). There is little difference Ni the deposition rates determined by the two methods at locations with very low deposition rates, i.e. <10 mg/(m2.d). On the other hand, at higher chloride deposition rates, the wet candle method gives deposition rates that are approximately twice as high as those given by the dry plate method. Both these measurements give values with low correlation for monthly samØng periods due to the great variation in weather characlenstics, A high correlation exists for annual average values (see Annex F).