Table 3 Comparison of different methods and their 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, PM_2.5, NO _X data; currently no real time analysis; wet deposition not detected.

Tephra detected moving south from Aberdeen to N. England on 24 May.