1. Comparison of NH3/NH4 and HNO3/NO3 measurements with DELTA minidenuders and impregnated filter methods
Robert Gehrig / Christoph Hüglin / Andrea Fischer
Claudia Zellweger / Elisabeth Wettstein
Empa: Swiss Federal Laboratories for Materials Testing and Research
CH-8600 Dübendorf Switzerland

2. Minidenuder; Schematic view
(Tang & Sutton, CEH, Scotland)
Minidenuder in NABEL

3. Impregnated Filter Measurements (Sum Measurements)
filter holder
impregnated filter for gases and aerosols
sodium hydroxide for HNO3 + NO3-
citric acid for NH3 + NH4+
aerosol particles
gas molecules

4. Impregnated Filter Measurements (Sum Measurements)

5. Impregnated Filter Measurements (Sum Measurements)

6. ammonia + ammonium nitric acid + nitrate
Comparison minidenuders vs. impregnated filters (Jan 2007 – Feb 2008) without corrections
ammonia + ammonium nitric acid + nitrate

7. Filtration efficiency (CPC measurements)

8. Minidenuder modifications
Second (acidic) filter: Whatman 1 replaced by Sartorius cellulose nitrate filter (0.45µm). No methanol in impregnation solution.
Analysis of ammonium and nitrate on both filters.
Later also analysis of ammonium and nitrate on all denuders and in the connecting tube.

9. Carry-over of ammonium in minidenuders (Nov 07 – Feb 08)
Sample # with additional analysis: NO3-Filter 1-8; NO3-Denuder 8; PFA-Tube 9-11

10. Carry-over of ammonium in minidenuders (Nov 07 – Feb 08)
Sample # with additional analysis: NO3-Filter 1-8; NO3-Denuder 8; PFA-Tube 9-11

11. Carry-over of nitrate in minidenuders (Nov 07 – Feb 08)
Sample # with additional analysis: NO3-Filter 1-11; NO3-Denuder 8-11; PFA-Tube 9-11

12. Carry-over of nitrate in minidenuders (Nov 07 – Feb 08)
Sample # with additional analysis: NO3-Filter 1-11; NO3-Denuder 8-11; PFA-Tube 9-11

13. Comparison minidenuders vs. impregnated filters (2008)
ammonia + ammonium (after corrections)
Rigi Payerne

14. Comparison minidenuders vs. impregnated filters (2008)
nitric acid + nitrate (after corrections)
Rigi Payerne

15. Conclusions
Systematically lower concentrations for minidenuders compared to impregnated filters.
Nitrate and ammonium were found in the connecting tube .
Nitrate was carried over to the second (ammonium) filter.
Nitrate also in the ammonia denuders? Tests continue.
After corrections good agreement between minidenuders and impregnated filters for "normal EMEP concentrations".
Still lower minidenuder results for very high concentrations? Tests continue.

16. Recommendations
Tube connecting nitric acid and ammonia denuders as short as possible.
Analysis of nitrate also on the second filter.
With these measures minidenuder results are consistent with results from impregnated filter measurements, at least for low and moderate concentrations.