1. Low-cost methods for gas/particle distribution of nitrogen species
Mark Sutton, Sim Tang, Eiko Nemitz, Neil Cape, David Fowler
Centre for Ecology and Hydrology (CEH) Edinburgh

2. Measurements of what? Gas concentrations of reactive nitrogen
HNO3, NH3
Aerosol concentrations of reactive nitrogen
NO3-, NH4+
Added species (in parallel, some methods)
Gaseous SO2, HCl
Aerosol SO42-, Cl-, base cations…

3. Why speciate between gas and aerosol?
Spatial patterns of gas and aerosol differ
Gas concs vary more locally
Sites may not be representative for gases
The transboundary contribution to aerosol concs can be larger than for gases
Temporal trends of gas and aerosol differ
With reductions in S, gas-aerosol partitioning has changed.
e.g. NH4+ aerosol concentrations have decreased substantially, while NH3 has not decreased much.

4. Why not just rely on daily filter-packs?
Method well established in EMEP
But are they really low cost?
Low capital cost, but high running cost for daily sampling.
Accept the need for high temporal resolution data
to examine relations to air mass origin at selected sites
But daily filter packs are expensive way to collect data of questionable quality
Well known artefacts between gas and particle phases

5. Example of artefacts with filter-pack sampling of NH4+ aerosol
FP and Berner Impactor compared against
Steam Jet Aerosol Collector (SJAC)
Warm conditions
Negative artefact
Cool conditions
Positive artefact
Artefact increases with sampling time
Nemitz (1998)

6. Filter-pack data only for total TIN & TIA
Eskdalemuir, UK
Which part is gas & which part aerosol?

7. High-cost solutions (Levels 2 and 3)
Daily annular denuder-filter combinations (e.g. Chemspec system)
Continuous denuder and Steam Jet Aerosol Collection methods
Strong desire for hourly frequency or better
See next presentation
AMANDA continuous denuder

8. Low-cost solutions (Level 1)
What is low cost?
Low capital cost (<€1k per site)
Low running cost (<€5k per site per year)
Typically monthly sampling
What is the role of these methods?
Seasonal and inter-annual trends
Spatial patterns with high site density
Dry deposition
Contribute to QA/QC of other methods

9. Example methods Passive samplers Long-term denuders
Can work well for NH3, but can also fail spectacularly
Methods must be continuously referred to an active sampling reference
Not available for HNO3 or aerosol
Long-term denuders
Provide a cheap reference method for all main gas and aerosol species

10. Passive sampling for ammonia
Most passive methods can be made to work if well operated and calibrated
Methods fail when not tuned for detection limits and when not properly calibrated (e.g. results out by factor 10!)
Many methods available, Gradko, IVL (Ferm), CEH (Alpha) Replication of sampling (min 3) essential for QC
ALPHA
sampler
Key (all samplers are cylindrical):
Sampler body
Sampler cap
Sampler membrane
Acidified filter/mesh
Circular supporting inserts

11. Example of change in passive sampling method – Stoke Ferry
Gradko tubes Alpha samplers
Data using UK wide calibration for passive methods

12. Long-term denuders (DELTA) DEnuder for Long-Term Atmospheric sampling
Tuned for monthly sampling: Good for local site operators and allows low sampling rate (0.3 l min-1)
Low sampling rate allows short (10 cm) denuders: Robust system can be sent by post to site operators)
Two denuders in series to allow QC on capture efficiency for every sample
Post-denuder filters to sample aerosol (first basic, second acidic)

13. Denuder for Long-Term Atmospheric Sampling (DELTA)
Cheap ~€800 for each complete system
Monthly sampling 50 times cheaper than daily monitoring
Double system (4 denuders in series) to include acid gases and other aerosol (SO2, HNO3, HCl, SO42-, NO3-, Cl- etc)

14. Architecture of full DELTA system
10 cm long denuder
coated with citric acid
14 cm long denuder
coated with K2CO3
Collect ammonia
Collect acids
10 cm long denuder
coated with citric acid
14 cm long denuder
coated with K2CO3
Collect anion aerosol
25 mm paper filter in K2CO3
25 mm paper filter in citric acid
Denuders from 6 mm i.d.
borosilicate glass
Collect NH4+ aerosol

15. Example HNO3 and NO3- data from full DETLA system

16. HNO3 network: gas & aerosol concentrations 2002
HCl
SO2
Na+
NO3-
Cl-
SO42-
Ca2+

17. Interpolated monitored NH3 and NH4+ concentrations
Methods: DELTA (monthly denuder/filter pack)
ALPHA (passive) at additional sites for gas only

18. Dry deposition monitoring
Time Averaged Gradient (TAG) system
Utilizes the DETLA approach with conditional
sampling for seasonal dry deposition estimates

19. How does the DELTA method compare with the daily FP data?

20. Monitoring sites and
results of prior modelling
Can we detect the return of livestock after foot & mouth disease in the NH3 record?
Study motivated by Dutch &
E. European experience of
difficulty to see trends
following emission reductions
Added Alpha sampling at ~20 targeted locations

21. Comparison of affected & unaffected areas around Cumbria
Monthly modelling
misses December peak
It is only possible to
detect the trend due to use of multiple sites

22. Conclusions
Low-cost denuder methods provide a robust and effective reference – including QC
Passive sampling can work for NH3, but not for aerosol
Use for regional monitoring of long term trends
DELTA method provides a tool for QA/QC of daily FP where that is used.

23. For further discussion
Practical considerations
Denuder coatings for warm climates (e.g. phosphorous acid)
Variant designs
DELTA as reference method for passive approaches (e.g. CEN TC264/WG11)
Agreeing data quality objectives
Establishing representativity of L2 and L3 sites in 50 km grids.

25. Importance of in-square variability
Dry NH3
Wet NH4
NH3 conc
5 km
50 km

26. Similarity of NH4+ at adjacent remote sites in N. Scotland

27. TIN and TIA at High Muffles

28. SO2 and SO42- aerosol at Eskdalemuir