CEH ALPHA Sampler. User Instructions. Issue Number 1. Penicuik, Midlothian EH26 0QB, UK. Bailrigg, Lancaster LA1 4AP

Transcription

1 User Instructions 1 Tang, Y.S, 1 Stephens, A and 2 Poskitt J 1 Centre for Ecology & Hydrology, Edinburgh Research Station, Bush Estate Penicuik, Midlothian EH26 0QB, UK 2 Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP Issue Number 1 Date 30/01/2017

2 Title CEH ALPHA Sampler CEH reference V1 CEH contact details Amy Stephens Centre for Ecology & Hydrology Bush Estate Penicuik Midlothian EH26 0QB Tel: +44(0) (reception) Tel: +44(0) (office) Fax: +44(0) Date 30/01/2017 ALPHA Sampler User Instruction - version 1.0 2

3 Contents 1 Introduction Preparation of ALPHA sampler filters for sampling ammonia Preparation of coating solution: 12 % (m/v) citric acid in methanol Preparation of coating solution: 2 % (m/v) phosphorous acid in methanol Preparation of coated filter papers Assembling ALPHA samplers Laboratory blanks Transport blanks CEH ALPHA samplers for monitoring NH Analysis of ALPHA samplers Extraction of acid coated filter paper Chemical analysis Calculation of air ammonia... 8 Calibration of ALPHA data Cleaning procedures for components... 9 Plastic components and PTFE membranes Contacts at CEH Appendix ALPHA components ALPHA Sampler User Instruction - version 1.0 1

4 1 Introduction The CEH ALPHA sampler (Figure 1) is a passive sampler for measuring NH3 in air. The sampler uses a citric acid coated filter, which serves to capture the ammonia for later analysis. A white PTFE (Teflon) membrane protects the filter whilst allowing gaseous ammonia to diffuse through for capture. The membrane is positioned facing downwards during exposure. The membrane end of the sampler is sealed with a protective cap whilst not being exposed. The passive sampling system consists of replicate ALPHA samplers attached to a shelter on a pole or post at about 1.5 m height above ground (Figure 2). Replicate samplers are used in order to give a more reliable estimation of the air concentration of ammonia. All samplers are supplied in a plastic container for protection. Figure 1: Outline diagram of a single ALPHA Sampler Figure 2: ALPHA sampler support on a metal post. ALPHA Sampler User Instruction - version 1.0 2

5 2 Preparation of ALPHA sampler filters for sampling ammonia Citric acid is suitable as an absorbent for temperate climates. Phosphorous acid should be used for hot, dry climates (avoid using in high humidity conditions). Oxalic acid is not recommended. 2.1 Preparation of coating solution: 12 % (m/v) citric acid in methanol Should be prepared fresh on the day of use. For 50ml coating solution, dissolve 6.0 g citric acid into 50 ml methanol. 2.2 Preparation of coating solution: 2 % (m/v) phosphorous acid in methanol Should be prepared fresh on the day of use. For 50ml coating solution, dissolve 1 g phosphorous acid into 2.5ml deionised water then make up to 50 ml with methanol. 2.3 Preparation of coated filter papers 1. Transfer the coating solution to a small capped bottle. 2. Arrange a number of filters on clean petri dishes, no more than 10 at a time. 3. Working as quickly as possible, accurately dispense 55 l aliquots of the coating solution onto the centre of each filter. 4. Place the petri dishes inside a desiccator. 5. Evacuate the desiccator by connecting it to a vacuum pump. 6. The impregnated filters should appear visibly dry after about 3 minutes. 7. The coated filters are now ready to be used, or they can be stored until required. 8. For storage, stack together inside a small petri dish sealed with either Parafilm and then placed inside grip-seal bags. This should in turn be stored in an airtight container. ALPHA Sampler User Instruction - version 1.0 3

6 3 Assembling ALPHA samplers Components will be shipped and labelled accordingly. 1. Place cap D inside cap B (tabs on caps in opposite direction, to avoid cap D being taken off when cap B is removed). 2. Place 27 mm PTFE membrane (C) inside the cap assembly, polypropylene backing (shiny side) facing outside and PTFE side (dull side) facing inside. 3. Place coated filter paper (F) inside the ALPHA sampler body, on top of the internal ridge. Ensure this is lying flat. 4. Place support ring (E) on top of coated filter paper. 5. Put the double cap + membrane assembly onto the sampler. Ensure that PTFE membrane is sitting flat. 6. As a further precaution against contamination, the prepared samplers should also be wrapped up with Parafilm. Note: The use of the top protective cap B over the membrane cap ensures that sampling does not start until cap B is removed. C (dull side) D B C (shiny side) Laboratory blanks For every batch of ALPHA samplers that you make, you will need to prepare laboratory blanks, which should be about 10% of the total number of samplers (minimum of 2). Laboratory blanks should be capped with solid cap A and covered with Parafilm. They should be prepared at the beginning and end for each complete batch of ALPHA samplers, and at regular intervals throughout. Place the blank samplers inside a plastic container and then place the containers in a labelled gripseal bag. Store the blanks in an airtight plastic box in a cool clean environment away from direct sunlight, preferably in a fridge / coldroom at 4oC Transport blanks Transport blanks are prepared in exactly the same way as samples and should be provided at regular intervals (and clearly marked), but these are left sealed and should be left in the carriage box. ALPHA Sampler User Instruction - version 1.0 4

7 4 CEH ALPHA samplers for monitoring NH3 Wear gloves at all times and avoid breathing directly on the samples SETTING OUT Contents of kit in klip lock box: 3 ALPHA samplers with solid cap B on 3 replacement solid cap A Remove top protective cap B (embossed writing on cap). Press down lightly on the rim of the membrane cap D to ensure that it is on securely and has not loosened during removal of protective cap B. Attach the samplers firmly to the Velcro of the shelter provided. * Note the date and time on the recording card, plus any relevant observations. *shelter with additional clips to keep samplers secure in high winds. ALPHA Sampler User Instruction - version 1.0 5

8 COLLECTING IN At the end of exposure period, remove ALPHA samplers. Put top protective cap (B) (with embossed writing) back on the membrane cap (D). Place sampler in klip lock box. Record sampling information on record card provided. Find somewhere dry for next step as rain water will contaminate the filter. Remove both cap B and membrane cap D with PTFE membrane. Do not touch the filter paper. Cap the samplers immediately with the solid cap A. Ensure that the cap is secure. The PTFE membranes are cleaned for reuse, so please take care when handling them. Put EVERYTHING back inside the container ALPHA Sampler User Instruction - version 1.0 6

9 5 Analysis of ALPHA samplers Extraction of acid coated filter paper 1. Exposed samples should be stored at 4C until analysis. 2. Dismantle ALPHA sampler; using clean tweezers, lift the coated filter paper out of the sampler and place into a small sample pot. 3. Add 3 ml deionised water to the filter paper in the pot. Cap the pot with a clean cap, label with sample name and leave to extract for at least one hour. Repeat this extraction with all of the samples (including a suitable number of blanks), noting the time at which the extraction process commenced. 4. Using a pair of clean tweezers (rinse the tweezers with deionised water in between different samples), pinch an edge of the filter paper and dunk it up and down in the extractant a few times to ensure that all the chemical species of interest enters into the extractant, and that the solution is well mixed. 5. For analysis on the AMFIA (AMmonia Flow Injection Analysis system), 1.5 ml of extracted solution is decanted into 3 ml auto sampler tubes. Care should be taken to ensure that any bits of loose fibres coming off the filter paper are not decanted into the auto sampler tubes, which may cause blockage in AMFIA Chemical analysis The extracted samples are analysed for ammonium on the AMFIA/SEAL at CEH. The calibration range normally used is 0-10 ppm (0.1 ppm, 1 ppm and 10 ppm calibration standards), and the QC's used are 0.2 ppm (low QC), 0.9 ppm (high QC), 2 (low QC) and 9 ppm (high QC). It may be necessary to dilute the extracted samples and repeat the analysis if they are outside the calibration range. ALPHA Sampler User Instruction - version 1.0 7

10 6 Calculation of air ammonia All passive samplers operate on the principle of diffusion of gases from the atmosphere along a sampler of defined dimensions onto an absorbing medium, according to Fick s law. The theoretical uptake rate of a sampler is a function of the length, L (m) and the cross sectional area, A (m 2 ) of the stationary air layer within the sampler, and can be calculated provided that the diffusion coefficient, D (m 2 s -1 ) of the gas of interest is known. The diffusion path length is nominally the distance from the mouth of the sampler to the reaction surface at the other end of the tube. Disturbance to the stationary air layer, such as through the effect of wind turbulence, can shorten the nominal path length. Conversely, the use of a turbulence-damping membrane at the inlet can increase the effective path length due to a quasi-laminar layer of air forming adjacent to the outside of the membrane. The effective volume of air sampled (V, m 3 ) by the CEH ALPHA sampler is given by: V = DAt/L (1) Where: t = time of exposure (h) D = 2.09 x 10-5 m 2 s -1 at 10C A = x 10-4 m 2 L = m Therefore: V (m 3 ) = m 3 x t (h) (2) The air concentration of a pollutant (, e.g. µg m -3 ) can then be calculated as: = (me mb) / V (3) Where: me = amount of NH3 collected on sample (µg) mb = amount of NH3 in blank sample (µg) Calibration of ALPHA data The ALPHA sampler has a gas permeable membrane placed at the inlet to establish a turbulent free layer of air inside the sampler. The membrane does however impose an additional resistance against gas diffusion, which needs to be taken into account when deriving a sampler s effective sampling rate. This can be determined empirically from field calibration of the ALPHA sampler against a suitable reference method. In practice, the membrane resistance equates to an extra 2 mm path length, but this should be confirmed by the laboratory against a recognised reference method. The effective uptake rate for the ALPHA sampler, based on field calibration against the DELTA system at 12 UK monitoring sites in the UK NAMN ( has been determined as: V (m 3 ) = m 3 x t (h) (4) ALPHA Sampler User Instruction - version 1.0 8

11 7 Cleaning procedures for components Plastic components and PTFE membranes 1. Remove all labels, and disassemble all components before washing, 2. Soak in 9pprox.. 1 % Decon (or equivalent lab. Detergent) solution for at least an hour or overnight (up to 24 hours), 3. Rinse several times with tap water, 4. Rinse 3 times with deionised water. 5. Spread components onto plastic trays (rinse trays with deionised water first) and dry in oven at 30-40C, 6. Remove all components as soon as they are dry. Never leave them in the ovens longer than necessary, to minimise contamination. 7. Wear gloves at all times when handling clean components. ALPHA Sampler User Instruction - version 1.0 9

12 8 Contacts at CEH In the case of any queries, please do not hesitate to contact: Ms Amy Stephens phone +44 (0) amstep@ceh.ac.uk Website: ALPHA Sampler User Instruction - version

13 9 Appendix ALPHA components A D E G B C F H A B C D E F Replacement solid cap Top protective cap 5µm PTFE membrane (27 mm diameter) Cap with hole for membrane Support ring (6 mm height) Filter paper G Internal ridge to support filter paper H Extended body for ease of handling Figure 1: Components of a single ALPHA sampler. I Figure 2: Assembled ALPHA sampler. ALPHA Sampler User Instruction - version

14 ALPHA Sampler User Instruction - version