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Experience from the EMEP VOC measurements

* Explore EMEP VOC monitoring results since 1992, analysis methods, intercomparisons, and implications for compliance monitoring and modeling activities. Evaluate trends in VOC emissions and their impact on air quality modeling. *

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Experience from the EMEP VOC measurements

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  1. Experience from the EMEP VOC measurements EMEP TFMM Workshop Oslo 22-24 November 2004 Sverre Solberg NILU/EMEP-CCC

  2. EMEP VOC measurements • VOC measured regularly since 1992/-93 • 5-15 monitoring sites depending on the year

  3. The objectives of the VOC monitoring • Establish the ambient concentration level • Compliance monitoring • Support the modelling activity • After 10(+) years: • Is the quality/precision of the data sufficient? • What can be said about compliance/trends? • What is the value for the modelling?

  4. EMEP VOC measurementssampling and analyses • Measurements twice pr week • Hydrocarbons • spot samples in canisters sampled around noon • Analysed by GC/FID • C2 – C7 compounds detected (method developed for C2-C5 compounds) • Detection limit around 10 ppt(v) • Carbonyls • 8h samples in DNPH adsorption tubes • Analysed by HPLC/UV

  5. QA/QC for VOC monitoring • Procedures for sampling/analyses etc given by the EMEP manual • But no DQOs specified yet • Manual inspection of data and detection of outliers by local lab and CCC • Intercomparisons/parallel studies • Audits from CCC (to Germany and Spain until now, more to come...) • Close collaboration between CCC and national labs in the beginning (education, training courses, visits from CCC to all labs)

  6. EU-project AMOHA intercomparison study of NMHC

  7. AMOHA (contd.)

  8. Parallel carbonyl measurements, France • 2 ½ years of parallel anlyses of carbonyls at FR08, Donon. • Formaldehyde, acetaldehyde, acetone: • High correlation, but bias (FR02 < NILU)

  9. Parallel carbonyl measurements, France • Other carbonyls: • Spikes more frequent • Lower correlation • Different blank values/detection limits

  10. Parallel carbonyl measurements, France • ”Tracers of isoprene” (MVK and MACR) + tracers of aromatics (glyoxal) • Very poor agreement • Values close to detection • Any value for modeling? • Either improve analyses or leave out?

  11. Parallel carbonyl measurements, Germany • UBA reports formaldehyde, acetaldehyde and acetone. • High correlation, but bias (UBA > NILU) • Acetone problem solved in 2000. Very good agreement after that. 

  12. Trends in VOC emissions • Nearly constant until 1990 • 36% reduction from1990 to 2002 according to official data

  13. Trends in measured VOCWaldhof 1992-2002 • Decline in winter median concentrations for all components • Strongest decline for iso-alkanes and benzene • Level off last years? • Varying meteorology  Modelling of NMHC needed to draw conclusions!

  14. Trends in measured VOC, Kosetice 1992-2002 • Less clear trends in measured winter medians • Increased winter medians last years  due to meteorological variations?

  15. Trends in measured VOC (UK) • UK (sub)urban VOC monitoring network indicate marked reductions during 1994-2000 

  16. Measured and modelled formaldehyde

  17. Measured and modelled ethene

  18. Measured and modelled ethene

  19. Measured and modelled isoprene

  20. Do we measure the right VOCs? • Derwent et al. (2003) ethanol and trimethylbenzenes important ozone precursors not measured today. • Significant fraction of VOC emitted as C6-C12 not measured today.

  21. Conclusions • Are the quality/precision of the data sufficient? • Hydrocarbons: • Very good agreement for many NMHC when using the same NPL standard for calibration. • Large differences seen for labs using other procedures/standards for calibration • NPL standard should be used. • Carbonyls: • High correlation but bias for formaldehyde, acetaldehyde, acetone.  Intercomparisons recommended • Variable agreement for other carbonyls. Procedures should be re-evaluated. Further audits needed. • DQOs should be specified. • Metadata for techn. procedures should be reported together with the data

  22. Conclusions (contd.) • What can be said about compliance/trends? • Long-term VOC measurements do indicate reduced general concentrations, but: • Year-to-year variations in meteorology  Compliance monitoring is (almost) impossible without supporting modelling • Modelling of individual NMHC species should be done to strengthen the basis for drawing conclusions

  23. Conclusions (contd.) • What is the value for the modelling? • Agreement with winter episodes of hydrocarbons • confidence in emission pattern in general • Good agreement for isoprene at some sites (in spite of short lifetime etc) •  confidence to emission algorithm for isoprene • Good agreement for formaldehyde •  confidence to photochemical formulation in the EMEP chemistry • Discrepancies could be used for model improvement • Summer peak of formaldehyde at Utø observed, not modelled • Use differences in VOC speciation for different transport directions to investigate differences in VOC emission speciations

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