Table 3 Comparison of different methods and their results
From: UK monitoring and deposition of tephra from the May 2011 eruption of Grímsvötn, Iceland
| Method | Operator | Grainsize | Coverage | Advantages | Disadvantages | Results |
|---|---|---|---|---|---|---|
| Tape-on-paper samples | Public | > 20 μ m | 87 locations | Wide coverage; quick and easy to analyse; ad-hoc network created quickly. | No further analysis possible; effect of rain on tape unknown; possible local contamination. | Tephra identified in Scotland on 23–24 May |
| Rainwater (tephra samples) | Met Office (+ public) | > 10 μ m | 21 locations | Can record grainsize and mass loading of wet and dry deposition; small additional cost to existing network; tephra can be analysed by SEM. | Contamination by inorganic dust; difficult to identify smaller shards; detailed analysis is time consuming; possible contamination. | Tephra possibly detected on 23–25 and 26–27 May with most confident identification north of 54°N. |
| Rainwater (chemistry) | Public (via SEPA) | n/a | 47 locations | Wide coverage; existing network used; easy to analyse. | Doesn’t give mass loading or concentration; mainly useful for wet deposition. | High Fe, Mn, Al concentrations in N. Scotland 23–25 May; no F or pH anomaly. |
| Pollen slides | Met Office | > 10 μ m (smaller in context) | 2 locations | Excellent constraint on timing; wet or dry deposition possible; small grains identifiable in context; potentially wide coverage. | Standard petrographic methods difficult on stained slides, which are destroyed by further analysis; network operates in summer only. | Tephra identified on 24–25 May (Eskdalemuir and Exeter) and 27 May (Eskdalemuir). |
| PM data | AURN, SAQD, SEPA | < 10 μ m | 105 locations | Wide coverage; excellent constraint on timing and near real-time results. | High risk of contamination by local sources; wet deposition not detected. | PM10 spikes at most locations in north and west UK on 23–24 May. Also elevated levels on 25–26 May in central Scotland. |
| Non-primary PM data | AURN | < 10 μ m | 45 locations | Good coverage; reduced risk of contamination by local sources. | Requires simultaneous collection of PM10, PM2.5, NO X data; currently no real time analysis; wet deposition not detected. | Tephra detected moving south from Aberdeen to N. England on 24 May. |