Sequential Air Sampler, Type SS2000
The NILU SS 2000 Sequential Air Sampler is a user-friendly automatic filter sampler. The sampler may be used for gases which can be absorbed on impregnated filters or other kinds of substrates e.g. the iodide absorption method for NO2 developed by Ferm and Sjödin (1993).
A programmable logic controller (PLC) controls the NILU SS 2000. The flow is set with a restrictor and measured with a mass flow meter. The sample volumes are recorded in standard litres accumulated over the sampling period. The user can set the desired start time for 8 samples in a sequence. The sampling will normally start at the same time every day at 24 hours interval.
The SS2000 Series of sequential Air Samplers are optionally delivered as a wall model or as a bench model with 8 filter holders in a sequence.
Measurement Principle
NO2
Ambient air is drawn at 0.5 litre per minute through an air intake funnel, a particle pre-filter and glass sinter filters. The glass sinter filters are impregnated with sodium iodide (NaI) and sodium hydroxide (NaOH). Nitrogen dioxide (NO2) is absorbed in the sinter filter, and the iodide reduces the NO2 to nitrite (NO2-). The nitrite formed in the sinter filters is extracted with de-ionised water. The concentration of nitrite is then determined with spectrophotometry (Griess method). The pre-filter introduced in front of the sample manifold is installed to remove particulate matter. Exposed samples are stable for several weeks, which allows transfer to a central laboratory for analysis.
Measurement range
NO2
With a sampling period of 24 hours, the measuring range for NO2 is 0.1 to 10 µg NO2/m3N when 4 ml is used as the extraction volume. Higher concentrations can be measured using a larger extraction volume.
Sampling efficiency
NO2
The sampling efficiency is higher than 98% with a flow rate of 0.5 l/min (lpm) at 15% RH. The efficiency is better than 98% at 60% RH even up to 4 lpm.
Air inlet and tubing
An inverted funnel is used to prevent precipitation from entering into the sample line. The funnel and tubing is either made of teflon (PTFE or FEP), polypropylene (PP), polyethylene (PE) or borosilicate glass.
The sampling line from inlet to filter manifold should be as short as possible.
Flow control
The present flow control is passive. A glass capillary tube sets the flow. The mass flow sensor records and stores the accumulated volume for each sample. The flow meter is calibrated at 25°C and 1013.25 mbar. The flow meter should be checked with a reference flow meter.
