BS/EN 16868-2019 pdf download.Ambient air – Sampling and analysis of airbone pollen grains and fungal spores for networks related to allergy – Volumetric Hirst method.
7.2 Integrated uncertainty assessment
According to LID] 111), a distinction is to be made between the following key types of variation in the estimation of measurement uncertainty for the pollen measurement methods described in this standard:
— Physical variation: variation due to physical influences, caused, for example, by spatial variation in pollen occurrence and dispersion by the air (spatial representativity).
— Instrumental variation: device-related variation caused by the technical features of the pollen trap and the sample preparation.
— Human error: inter- and intra-observer variation during identification and counting; this factor also includes counting error.
7.3 Uncertainty from counting error and counting routine
The uncertainty from counting error depends: a) on the number of pollen particles counted and b) on the personal skill of correct identification.
The correct identification of pollen types under the microscope and hence the determination of the measured value depends decisively on the well trained analyst.
The counting error from the statistical side depends on the number of particles counted and follows a Poisson distribution. The error increases with lower number counts, especially for counts lower than 10. As the number of particles counted depends on the counting area, too, one of the minimum requirements, which aims to minimize the counting error, concerns the specification of a minimum counting area in case of low number counts.
7.4 Measurement uncertainty relating to sampling efficiency
Sampling efficiency varies for the larger spores and pollen grains of relevance here. The measurement uncertainty under real-life conditions can only be given descriptively. Deviations in sampling efficiency are to be expected in the usual range of 90 % to 55 % [7], although significant upward or downward excursions are possible in individual cases. Sampling efficiency can exceed 100 %, particularly with heavy particles and at higher wind speeds.
7.5 Measurement uncertainty relating to capture film, adhesive and specimen preparation
Material- and process-related measurement uncertainty occurs in relation to capture film, adhesive and specimen preparation. Since deviations depend strongly on such ambient conditions as air temperature, relative humidity, heating of the device on exposure to the sun etc., a quantitative estimate can only be approximated case specific, e.g. by parallel measurements.
This method involves the direct optical microscopy detection of discrete units (particles, in this case pollen grains/spores), so the detection limit is one pollen grain or spore per counting area. Assuming counting is performed across the full width of the capture trace, the detection limit can be improved to a maximum of I pollen grain or spore per daily capture area, corresponding to I pollen grain or spore per 14,4 rn3 per day, corresponding in turn to an absolute detection limit of 0,07 n/rn3 (see 6.3.6).
7.8 Measurement uncertainty in relation to the calibration of the flow rate
The accuracy of the calibration depends on the air resistance and characteristic curve of each trap, vacuum pump and how meter used.
This type of error has to be shown to he considerable [10]. It shall he declared as less than 10% by a certificate which has to be provided by the manufacturer.
7.9 Measurement uncertainty relating to spatial representativity
The pollen concentration measured at a measurement site is interpreted in terms of pollen exposure in the surrounding area [181. In general, the spatial representativity of point sampling is limited. Accordingly, uncertainty related to this aspect has to be taken into account.
The pollen concentration values measured at the measurement sites shall be related as far as possible to the results from surrounding pollen measurement sites and to other data sources. e.g. with phenological observations, meteorological data and allergy reports.
8 Quality assurance
8.1 General
Quality assurance measures are to be undertaken with regard to measurement sites, analysts, laboratories and the monitoring network
8.2 Measurement site/trap
8.2.1 Control
The installation and operating conditions shall be checked at least once per year and/or at the beginning of the pollen season, according to the Instructions of the manufacturer.
A check list for the device control may be done (electric power, vacuum pump, ball bearing, stability, horizontality, clockwork, cleanliness, etc.) and any failure shall be reported to the manager.
The operator of the trap shall be trained on a regular basis for checking all the parameters and the functions of the device, including cleaning of the trap (orifices. ring, etc.), changing the drum, how control, etc.BS/EN 16868-2019 pdf download.
BS/EN 16868-2019 pdf download
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