Uncertainties in atmospheric observations Wenche Aas EMEP/CCC

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Sources of uncertainties  Sampling and analytical method  Detection limit  Interference  Instrument drift, calibration  Positive or negative artefact  Sampling procedure  Contamination  Temperature and period for storage  Transport  Representativity.  Local farming (NH3)  Nearby roads (NOx; O3)  Dust (PM, Ca..) Lab- and field intercomparison Field inter- comparison; model comparison Repr. studies, i.e passive sampling. Model comparison

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Monitoring programme: Level 1 Main ions in precipitation and in air heavy metals in precipitations ozone PM 10 and PM 2.5 mass meteorology at ca 125 sites Level 2, supersite (joint EMEP/GAW) POPs Heavy metals in air and aerosols VOC EC/OC, OC speciation Mineral Dust PM speciation incl. gas particle ratio + all level 1 activities sites Both levels are mandatory by all Parties

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Data quality objectives  Acidifying and eutrophying compounds o 15-25% uncertainty in annual average (10-15% for indiv meas.)  Heavy metals o 30% uncertainty in annual average (15-25% for indiv meas.) o 40 % uncertainty for As, Cd, Ni in the EU 4 th DD (70% in dep) o 50% uncertainty for Hg (total gas) in the EU 4 th DD  POPs (not defined in EMEP) o 50% uncertainty for PAH in the EU 4 th DD (70% in dep)  PM (not defined in EMEP) o 25% accuracy in continuous measurements EU 1 st DD  Photooxidants (not defined in EMEP) o: 15% accuracy in continuous O3, NOx measurements, EU 3 rd DD

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Lab intercomparisons annually, 2005 Spread: 2RSD % Bias: RB %

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 WMO ICP

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Preila (LT) using filterpack SO 2 field intercomparison Zarra (ES), abs (H202) and monitor TCM ain Germany (historic data) at DE09 (left and DE03 (right)

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 SO 2. UV fluoresence monitor, interference

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 NO 2. Chemiluminisence (Mo converter) Not selective for NO 2

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 QA flag Lab flag Field flag Green: Bias < 10% Spread <20% (S,N) Blue: Bias < 40% Spread <40% (S,N) Green: Bias < 10% Spread <25% Blue: Bias < 50% Spread <50%

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 QA Flag for main ions in 2005 In precip In air  Analysis in lab are in general better than 20% (both in air and precip)  Total uncertainty (field intercomp):  about half the measurements is better than 25%  rest better than 50%

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Lab intercomparison of HM annually Average per cent error, 2005

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Hg intercomparison at DE02 in 2006 Tot Hg (g) in air Tot Hg in precip

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Heavy metal deposition, CEN WG20 Birkenes, comparing wet only (analysed at UBA) and bulk (NILU)

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Parallell wet only, CEN WG 20 FromTo Cd9%18% Pb7%15% As6%19% Ni11%20% Relative SD in deposition measurements :

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 POP lab intercomparison,2002

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Artefact in gas/particle for N IT01, Jan 2007 IT01, June 2007 Artefact free measurements using denuders only done at Montelibretti Underestimation of N

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Estimates of the positive artefact of OC in PM 10 and PM 2.5 /PM 1 -June 2006 QBQ-approach

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Measurement and model intercomparison ?? NO ES

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Uncertainties in trends SO 2 SO 4 in air

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Representativity, NO 2 Comparing EMEP model and obs. in light of population density ES07 IT01 NL91 AT02 BE32

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Conclusions  Many factors influence uncertainty in measurements  Methodology, sampling procedure, Representativity  Need to distinguish between uncertainty in one data point, in averages and trends; and distinguish between bias and spread  In general, the measurements are within DQO if reference methods are used and the site is representative, but there are exceptions  Need to have better control of artefacts, especially nitrogen gas/particle and EC/OC  More intercomparison of other species than main comp and HM are needed

Wenche Aas, Measurement uncertainty. TFMM/TFEIP Dublin 22 Oct 2007 Data quality objectives  Acidifying and eutrophying compounds o 15-25% uncertainty in annual average (10-15% for indiv meas.)  Heavy metals o 30% uncertainty in annual average (15-25% for indiv meas.) o 40 % uncertainty for As, Cd, Ni in the EU 4 th DD (70% in dep) o 50% uncertainty for Hg (total gas) in the EU 4 th DD  POPs (not defined in EMEP) o 50% uncertainty for PAH in the EU 4 th DD (70% in dep)  PM (not defined in EMEP) o 25% accuracy in continuous measurements EU 1 st DD  Photooxidants (not defined in EMEP) o: 15% accuracy in continuous O3, NOx measurements, EU 3 rd DD