I will now describe how I work with my samples. The aerosol sample used in this experiment was collected at Risø, Denmark from 26^th April to 2^nd May, 2011 (Risø LFG, 2011.0017), with an air flux of 54600 m³ and total filter weight of 77.7 g.

I applied the following procedure to separate all fractions of aerosol. Maybe it’s a little detailed. My aim with this experiment is to see in what proportions the main species of inorganic iodine exist in the sample. The two species are iodine (I^-) and iodate (IO₃^-)

1         Water leaching

1.1   Cut the air filter to pieces with size of about 1 cm², weigh 1g to a 100 ml beaker. Add 50 mL water to immerse the filter. Stir the solution overnight at room temperature, and record the leaching time.

1.2   Afterwards pour slightly the supernatant to a beaker with known weight, add 50 mL water to leach iodine for 0.5 h for the second time. Filter the solution by suction filtration. Combine the filtrate with the first supernatant and record the weight.

1.3   Shear the filter and combine with air filter into the first beaker for NaOH leaching.

Fig 1. Aerosol leaching with water or NaOH solution

1.4   Separation of iodine in water leach

1.4.1     Add 125I tracer to water leachate (the I125 is a radioactive iodine isotope that we add in known amounts to the sample so we can see how much is still left after the isolation of iodine. We loose the same amount of each iodine isotope so if 50% of the I-125 is lost it means 50% of I-129 is also lost)

1.4.2     Pass the water leach through an anion exchange column of 10 cm height and 1 cm diameter. Collect the leach with a known weight beaker as iodate. Use 25 mL 0.2 M NaNO3 and 15 mL water to wash the column, combine the washes to iodate.

1.4.3     Take 9.9 g the iodate fraction (leach + washes) with addition of 0.1 g concentrate NH3H2O to direct ICP-MS measurement for 127I.

1.4.4     Use 50 mL 1% NaClO and 10 mL 3 M HNO3 to elute the iodide to a known weight beaker. Adjust pH to neutral, and record the weight of the eluate. Take 6 g to measure the 125I counts for calculation of chemical yield.

1.4.5     Take 9.9 g the iodide fraction (eluate) with addition of 0.1 g concentrate NH3H2O to direct ICP-MS measurement for 127I.

Fig 2. Separation of iodide (I^-) and iodate (IO₃^-) in water leachate with anion exchange chromatography

2         NaOH leaching

2.1   Add 50 mL 0.5 M NaOH to immerse the filters in the beaker, stir for 4 h under 60℃ with cover of watch dish.

2.2   After pour slightly the supernatant to a known weight beaker, add 50 mL NaOH to leach iodine for 0.5 h for the second time. Filter the solution by suction filtration. Combine the filtrate with the first supernatant and record the weight.

2.3   Take 1 g the NaOH leach to be diluted to 10 g with 1% NH3 H2O, and then measured by ICP-MS for 127I.

3         Residue combustion

3.1   Shear the filter and combine with the other filter into a quartz boat for combustion separation of iodine. Add 125I tracer to monitor the chemical yield.

3.2   Quartz wool is stuffed to the combustion tube at the end of outlet. Slow heating is necessary to avoid rapid inflammation of air filter that is polypropylene with thermal decomposition temperature of about 350～380℃ and melting point of 167 ℃ and to prevent incomplete combustion. Based on the properties of polypropylene, temperature will be set as Table 2.

3.3   35 mL trap solution was used to absorb iodine released from combustion. Wash the outlet of the tube and combine the wash with trap solution. Take 6 g solution for 125I measurement and chemical yield.

3.4   Take 1 g the trap solution (plus wash) to be diluted to 10 g with 1% NH3 H2O, then measured by ICP-MS for 127I.

Fig 3. Combustion analysis for total aerosol or aerosol after leaching, combustion boat (left) and bubbler (right)

4         Target preparation and measurement of 129I

4.1   According to data in southern Sweden (Englund et al. 2010), 129I/127I ratios vary from 10^-8 to 10^-6, 3.5 mg 127I carrier will be added to final ratios of 10^-11 in iodide to 10^-9 in NaOH leach. Therefore, 2 mg WWI carrier will be added to total iodide, iodate and residue fractions, while to one fifth volume of NaOH leach.

4.2   All aqueous solutions are extracted with CHCl3, and iodine was precipitated with 0.5 M AgNO3.

Fig 4. Water or NaOH leach (left) and extraction apparatus (right)