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

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

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?

EMEP VOC measurements sampling 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

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)

EU-project AMOHA intercomparison study of NMHC

AMOHA (contd.)

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

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

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?

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. 

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

Trends in measured VOC Waldhof 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!

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

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

Measured and modelled formaldehyde

Measured and modelled ethene

Measured and modelled ethene

Measured and modelled isoprene

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.

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

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

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