Achievements in monitoring climate change and future challenges for gas metrology

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1 Achievements in monitoring climate change and future challenges for gas metrology Martin J.T. Milton NPL, Teddington, UK Friday 20th July 2012 Varenna

2 Amount fraction [mmol/mol] The Atmosphere Ref CIPM 81/91 Revised in Kaye and Laby

3 The IPCC Assessment Reports - contributions to radiative forcing Today s talk C C Q M G A W G

4 Contributions to radiative forcing with chemistry C C Q M G A W G

5 Today s talk Quantification Control Carbon CO 2, N 2 O, & halocarbons Particles CO, CH 4, & trace halocarbons Water vapour Ozone O 2 VOCs C C Q M G A W G

6 The coherence of measurement results Definition (conventional) scaling factors do not appear when (measurement) equations are combined I use coherence to mean that Results for different compounds and from different methods can be brought together Strong coherence measurements of different compounds are equivalent Weak coherence measurements of a compound made by different methods are equivalent

7 The coherence of measurement results Coherence Formal definition (conventional) scaling factors do not appear when (measurement) equations are combined I use coherence to mean that Results for different compounds and from different methods can be brought together Strong coherence measurements of different compounds are equivalent Weak coherence measurements of a compound made by different methods are equivalent

8 Atmospheric CO 2 Concentration The Keeling Curve Historical Value 280 ppm

9 Atmospheric CO 2 Concentration The Keeling Curve Target set for data quality +/- 100 ppb (NH) +/- 50 ppb (SH)

10 Global atmospheric CO 2 Atmospheric CO 2 Concentration The flying carpet Target set for data quality +/- 100 ppb (NH) +/- 50 ppb (SH)

11 Monometric method for CO 2 standards NOAA/GMD Method Precision measurement of P, T and V of gas in two quartz volumes Whole sample in 6l volume CO 2 and N 2 O frozen out and measured in 10 ml volume Composition of CO 2 and N 2 O calculated using virial equations. N2O measured independently and subtracted. Repeatability of 0.02% (relative) Zhao et al, J Geophys Res 102 (1997)

12 WMO method for CO 2 scale dissemination Repeatability ~ 100ppb Niwot Ridge air Noise (1 sec) ~ 20ppb Volumetric addition of pure CO 2, CH 4 etc Value on certificate are expressed as on a scale

13 CCQM-K52 (2006) carbon dioxide in air Participation of WMO laboratory in Australia The WMO scale and the SI values from NMIs agree C C Q M G A W G

14 New NPL method for CO2 dual scale / SI values Purified air % N2, % O2, 0.93 % Ar Coherence CO 2 <1 ppm CH 4 < 10 ppb CO < 10 ppb Precision (5 min) 25 ppb Analysed by GC-DID against air gravimetrically spiked with trace CO 2 and CH 4 Gravimetric addition of pure CO 2, CH 4 etc Certificate will show: Value from comparison with WMO scale, and Value from preparation (SI) Commercial CO 2 blended with 13 CO 2 to achieve close to d 13 C of 8 per mil

15 Global traceability for methane CCQM-P41 CH 4 at 1.8 mmol/mol) 2002 DQO for GAW CCL is 2 ppb (0.1%) Participation of WMO laboratory in Australia C C Q M G A W G

16 Plans for CCQM-K82 (methane in whole air) Participants: 7 NMIs + NOAA CH 4 /air (1.70 to 2.20 µmol/mol) Each participant will submit two standards of CH4/air Synthetic or ambient air (inc Ar and CO) Reference Value Calculated from GLS regression line to response data Comparisons carried out using CRDS and GC-FID methods Measurements during 2012/3 C C Q M G A W G

17 Trends in surface ozone at Mace Head, Ireland

18 Reference method for ozone ATTENUATED LIGHT INTENSITY I LIGHT INTENSITY I 0 OZONE SAMPLE T Temperature in the cells P Pressure in the cells L opt light path length D Product of transmittance of the two cells R Gas constant x mole fraction of ozone in dry air (nmol/mol) x 1 T R s L P N 2 opt A ln( D) N A Avogadro constant s Ozone absorption cross-section at nm at STP Bureau International des Poids et Mesures 18

19 NIST ISCIII ERLAP Environment Canada METAS SRP18 METAS SRP14 KRISS LNE VNIIM FMI WMO/WCC-EMPA UBA (A) SP NPL NDENW UBA (D) NIES CHMI CSIR-NML(1) NERI NILU NMi-VSL IMGC CSIR-NML (2) BIPM GPT NIES GPT Degree of equivalence (nmol/mol) International comparison of ozone D x x CCQM-P28 i (at L420 A B i nmol/mol) B I P M (k=2) Gas Phase Titration Bureau International des Poids et Mesures 19

20 NO standard Cross-section (cm 2 ) UV photometry and GPT traceability chains Pure ozone concentration c assessed by pressure measurements s ( ) Primary UV photometer I 0 I I 0 1 I s ( ) ln L I opt c I nm (Hg line) wavelength (nm) 1 I c' ln L opt s ( ) I0 Equivalent? Coherence NO x GPT stoichiometric reaction O 3 Chemiluminscence NO x analyser calibrated by gravimetric NO standard NO + O 3 NO 2 + O 2 Calibration of O 3 analyser

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22 Climate Change Quantification Control Carbon CO 2, N 2 O, & halocarbons Particles CO, CH 4, & trace halocarbons Water vapour Ozone O 2 VOCs C C Q M G A W G

23 What does metrology bring to studies of the environment? Traceability to the SI gives: Measurements that are stable Long-term trends can be used for decision making Measurements that are comparable Results from different laboratories can be brought together Measurements that are coherent Results for different compounds and from different methods can be brought together eg carbon dioxide, ozone, Coherence

24 A different paradigm - traceability to a scale Much of environmental science is focussed on measuring and identifying trends It has exploited the scale approach maintain links to (physically) the same standards for the longest term possible The NMI ( traceability ) approach seek to establish the best representation of the SI (updated whenever necessary). Uncertainty in trends (eg global T at 500 hpa) Trend of 0.2 K / decade

25 The basis for measurements The scale approach Rationale Values disseminated are traceable to a collection ( family ) of artefacts carefully, monitored and maintained The SI traceability approach Rationale Values disseminated are traceable to the Sl as realised by a primary method. Benefits Highly consistent ( precise ) Good trend data Disadvantages Responsibility / cost of maintenance concentrated at one institution Impossible to regenerate or develop independently (May be) insensitive to drift in the reference artefacts Benefits Highly coherent and accurate Good absolute data Possibility for more than one source. Coherence Disadvantages Values may change (in absolute terms) within stated uncertainties but will always improve. Traceability to the SI uniquely gives coherence

26 Mixing Ratio, pptv X Global monitoring of organics (eg ethane) Organic compounds are responsible, with NO x, for the photochemical formation of O 3 and other photo-oxidant pollutants including secondary organic aerosol. Ethane - lifetime of 1.5 months and strong seasonal dependence in concentration. Magnitude of the seasonal cycle is a sensitive indicator of hemispheric scale oxidising capacity. The emission sources of ethane are relatively well defined, and are strongly connected to natural gas (i.e. methane) and biomass burning emissions VOC - Trends at Hohenpeissenberg Ethane -2% /year Acetylene -3% /year Ethene -3% /year Benzene -4% /year Toluene -6% /year p,m-xylene -8% /year Eos of American Geophysical Union, Vol. 90, No. 52, 29 December 2009

27 Volatile Organic Compounds (VOCs) targeted for monitoring Ethane Ethene Propane Propene iso-butane n-butane Acetylene trans-2-butene 1-Butene cis-2-butene 2-Methyl Butane n-pentane 1,3-Butadiene trans-2-pentene 1-Pentene 2-Methyl Pentane n-hexane Isoprene n-heptane Benzene 2,2,4-tri Methyl Pentane n-octane Toluene Ethyl-Benzene m+p-xylene o-xylene 1,3,5-tri Methyl Benzene 1,2,4-tri Methyl Benzene 1,2,3-tri Methyl Benzene Formaldehyde NMHCs 17 target compounds chosen by WMO addressing ozone formation fugitive emissions biogenic emissions biomass burning aerosol precursors ocean emissions Ozone precursor compounds specified by EU Ozone Directive (2002/3/EC)

28 Preparation of primary VOC standards Passivated Cylinders NPL-pattern valves Micro-loop injections Pure compounds ethylbenzene m-xylene p-xylene o-xylene 1,2,4-trimethylbenzene 1,2,3-trimethylbenzene 1,3,5-trimethylbenzene benzene toluene Pre-mixtures 2.5ppm Intermediate parents Parent mixture 200ppb Final mixture 4ppb 100ppm 10ppm 200ppb 4ppb ppb concentration in 3-4 steps n-pentane 2-methylbutane 1-pentene trans-2-pentene isoprene n-hexane 2-methylpentane n-heptane n-octane 2,2,4-trimethylpentane n-butane i-butane 1-butene trans-2-butene cis-2-butene ethane ethene acetylene propane propene 1,3-butadiene Relative gravimetric uncertainty (k=2) 100ppm 12ppm 250ppb 5ppb 150ppm 18ppm 350ppb 7ppb 1.5 % 300 ppm 15ppm 300ppb 6ppb 0.03% % 0.05% % 0.13% % 0.18% 0.84% Standard mixtures of ambient VOCs in synthetic and whole air with stable reference values - R.J.P. Grenfell, M.J.T. Milton*, G.M. Vargha, C. Brookes, P.G. Quincey and P.T. Woods J Geophys Res (2010) 115 D14302,

29 Comparison of NPL primary standards

30 Estimate of the drift parameter 2 versions 3-8ppb 30 component ozone precursor standard Expanded uncertainty based on u a Now recognised as GAW Primary Standard for 8 hydrocarbons

31 VOC standards for the stations in the Global Atmospheric Watch of the WMO now provided by NPL C C Q M G A W G

32 From Andrew Manning and Ralph Keeling GHG Measurements Royal Society, London, 2010.

33 Coherence From Andrew Manning and Ralph Keeling GHG Measurements Royal Society, London, 2010.

34 Atmospheric oxygen/nitrogen ratio Through the 1990s oxygen concentration decreased more slowly than was expected from fossil-fuel consumption alone. This suggests that the earth's biosphere has acted as a source of oxygen and hence a sink for carbon dioxide. Challenge a global sink of 2Pg[C] causes 1.8 * mole change in global oxygen abundance change in atmospheric oxygen of %(relative) Absolute change of 160 mmol/mol in 0.32 mol/mol

35 Source of uncertainty sources in oxygen standards at the % level Keeling and Manning Tellus (2007) Achieved using standards stored and used horizontally in isothermal conditions. But these uncertainties refer to relative performance. Absolute standards are required.

36 Atmospheric water vapour Stratospheric water vapour concentrations decreased by about 10% after the year 2000, which acted to slow the rate of increase in global surface temperature over 2000 to 2009 by about 25% compared to that which would have occurred due only to carbon dioxide and other greenhouse gases Solomon et al; Science (2010) Significant difficulties with producing comparable data from different instrumental methods under field conditions.

37 H 2 O measurements at NMIs Coherence EURAMET Project 1002 Measurements of Trace Water Vapour NIST 1 NIST 2 NPL-GM PTB NMIJ

38 Atmospheric particles

39 Strong present-day aerosol cooling implies a hot future, Andreae et al, Nature 2005

40 EURAMET Airborne nanoparticle concentration Comparison of concentration measurement for pseudo mono-disperse size distribution (50 nm) and at two concentrations each.

41 Measurement challenges - nanoparticles Parameter Requirement Status Mass concentration eg PM 10 (μg/m 3 ) Number concentration (cm -3 ) Air quality regulation Vehicle emission regulation; atmospheric studies; workplace exposure Mature (but significant problems) Recent activity at some NMIs Size distribution (typically cm -3 /log(nm)) Atmospheric and health studies Highly instrument dependent Surface area concentration (μm 2 /cm 3 ) Composition etc.. Health studies Highly method dependent

42 Future Challenge Regional inventory verification Standards required to 0.05 ppm globally.

43 Where next? Commercial networks for environmental monitoring Earth Networks will invest $25 million to develop and implement networks that measure environmental factors such as air quality, water quality, wind and pollution

44 April 2010 The WMO sign the CIPM MRA Three institutes designated by the WMO can now participate fully in the MRA Others may follow. A new set of opportunities for collaboration and for the NMIs to support global atmospheric monitoring C C Q M G A W G

45 Where next? Low cost multi-species sensing msec timescales real-time data access

46 Deployment of 50 sensor nodes at LHR Deployed Not yet deployed

47 But.. how do we calibrate the data? S11 S12 S14 S16

48 What does metrology bring to studies of the environment? Measurements that are stable Long-term trends can be used for decision making Measurements that are comparable Results from different laboratories can be brought together Measurements that are coherent Coherence Results for different compounds and from different methods can be brought together eg carbon dioxide, ozone, trace water vapour These can all be achieved through a focus on traceability to the SI.