Presentación realizada en: 14th WMO-GAW Brewers Users Group Meeting celebrada en Tenerife del 24 al 28 de marzo de 2014

Burrows, J. P.

Casale, G. R.

Diémoz, Henri

Eleftheratos, Kostas

Hilboll, A.

Redondas, Alberto

Richter, A.

Savastiouk, Volodya

Siani, Anna Maria

Stanek, Martin

Vrekoussis, Mihalis

Zerefos, Christos S.

English

Savastiouk, Vladimir

Casale, Giuseppe Rocco

Burrows, John Philip

Richter, Andreas

Hilboll, Andreas

Agencia Estatal de Meteorología

Improvements to the nitrogen dioxide observations bymeans of the MKIV Brewer spectrophotometerH. Diémoz 1,2 A. M. Siani 2 V. Savastiouk 3 A. Redondas 4 K.Eleftheratos 5 C. S. Zerefos 5 M. Vrekoussis 6 G. R. Casale 2M. Stanek 7 J. P. Burrows 8 A. Richter 8 A. Hilboll 81ARPA Valle d'Aosta, 2Sapienza Università di Roma, 3IOS, 4AEMET, 5Academy of Athens,6EEWRC, 7HMÚ and 8University of Bremen14th WMO-GAW Brewer users group meetingTenerife, March 20141 Introduction2 Instrumental characterisation3 Updates to the algorithm4 Field measurement campaigns5 Reprocessing of long-term data sets6 Future researchIntroductionMeasurements with Brewer spectrophotometersMKIV426  453 nm (visible)original algorithm: Kerr (1989)updates (not implemented):Barton (2007)MKIII349  363 (UV-A)Cede et al. (2006)IntroductionMeasurements with Brewer spectrophotometersWhat's wrong with NO2 measurements using the Brewer?overestimations (>200%) with thecurrent algorithmI other ground-based instrumentsI satellite radiometersrandom deviationsI due to interferences (O4, H2O, Ring)I sensitivity to instrumental settings(e.g. wavelength misalignments)noiseI depends on both the algorithm andused wavelengthsno calibration service for NO2IntroductionMeasurements with Brewer spectrophotometersOpen questionscan we obtain better performances bychanging the operational wavelengths?how large is the measurementuncertainty?do direct sun and zenith sky estimatesagree within their uncertainties?how to perform a Langley plot with avariable absorber?is it possible to reprocess long-termseries?IntroductionMeasurements with Brewer spectrophotometersWhat was done1 mathematical framework and numericalsimulationsI accurate characterisation of Brewer#066I parameterisation of all influencingfactors2 updated spectroscopic dataset3 new (polarised) AMFs for ZS geometry4 variable-Langley calibration (Izaña)5 Montecarlo uncertainty budget6 reprocessing of 4 long-term series1 Introduction2 Instrumental characterisation3 Updates to the algorithm4 Field measurement campaigns5 Reprocessing of long-term data sets6 Future researchInstrumental characterisationFundamental to reveal the weak signal of NO2dispersionneutral density filterstemperature dependenceetc.[Diémoz et al., 2011, Brewer Meeting, Beijing]1 Introduction2 Instrumental characterisation3 Updates to the algorithm4 Field measurement campaigns5 Reprocessing of long-term data sets6 Future researchUpdates to the algorithmNoise reduction~γ · −→βR ≡ 0~γ · −−→αO3 ≡ 0~γ · −→δA ≡ 0~γ ·~1 ≡ 0~γ ‖ αNO26 slits =more degrees of freedom =noise reductionUpdates to the algorithmInterfering factorsConsidered factorsnoiseoxygen dimer (O4)water vapor (H2O)Ring effectsensitivity to NO2effective temperaturewavelengthmisalignments 00.010.020.030.040.05400 420 440 460 480 500opticaldepthwavelength (nm)totalO3NO2H2OO4CHOCHOUpdates to the algorithmIncreasing the DOF0123450 500 1000 1500 2000 2500 3000noise(DU)micrometer stepsFor every influencing factor a diagram was assessedand the optimal grating positions (i.e. wavelengths) were foundUpdates to the algorithmJump scans420 430 440 450 460 470 480wavelength (nm)a)b)c)11 slitsO4 and H2O included in the retrievalUpdates to the algorithmFurther updatesall cross sections were updated to recent laboratory measurements(NDACC 2012 guidelines)I NO2 - Vandaele 2002 @ 220 K (instead of Graham 1976)I O3 - Bogumil 2003 @ 223 K (instead of Vigroux 1952)I Rayleigh - Bodhaine et al. 1999 (instead of UV Brewer coefficients)I O4 - Hermans 2003 (previously neglected)I H2O - Hitran + Py4CATS (previously neglected)I0-effect taken into accountnew weighting factorspolarised AMFs for ZS geometry (SCIATRAN, full-spherical)Updates to the algorithmRadiative transfer calculations0.911.11.21.31.41.50 10 20 30 40 50 60 70 80DUsolar zenith angle (deg)[Diémoz et al., 2013, SPIE, Dresden]1 Introduction2 Instrumental characterisation3 Updates to the algorithm4 Field measurement campaigns5 Reprocessing of long-term data sets6 Future researchField measurement campaignsThe Izaña campaign38 days of measurements5 days removed because offog/rainno relevant contamination bySaharan dust on ratios2 days for initial checks16 days for direct-sunmeasurements (3 steps)15 days for zenith-skymeasurements (3 steps and 2polarizations)5 days for O3 and O4 direct-sunmeasurementsField measurement campaignsLangley in varying conditionsImproving the Langley: linear changes with timey(t)µ(t)=a1µ(t)+ b(t)=a1µ(t)− δ − ξt(1)Field measurement campaignsLangley in varying conditions(a δ ξ)T= A†(y1µ1... ynµn)T(2)Field measurement campaignsLangley in varying conditions-0.100.10.20.30.48 10 12 14 16 18NO2columndensity(DU)time(hours)Izana clim. (AM)Izana clim. (PM)linear fitsite reference daytime increasing rate (1013 moleccm2 h)Zugspitze/Garmisch Sussmann et al. (2005) 515Izaña Gil et al. (2008) 6Pacific Ocean Peters et al. (2012) 8.7±0.5Izaña present study 7.012.5Field measurement campaignsThe Izaña campaign-0.4-0.200.20.40.60.81-40 -30 -20 -10 0 10 20 30 40DUairmassdirectzenith (parallel)zenith (perpendicular)Measurements using the three different geometries are equivalentwithin their respective uncertainties(airmass < 0 morning; > 0 afternoon)Field measurement campaignsThe Izaña campaign0.060.070.080.090.10.110.120.130.140.150.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15Brewer(DU)NDACC (DU)fity=xThe Brewer does not overestimate anymoreField measurement campaignsComparison among different algorithms-0.2-0.100.10.20.30.40.50.6260 262 264 266 268 270 272 274 276DUdayIzaña (2012)  Pink: Kerr's algorithm;green: filters and Rayleigh updates; blue: new algorithm.Field measurement campaignsUncertainty budget00.050.10.150.20.250.30.350.410 20 30 40 50 60 70 80NO2uncertainty(DU)solar zenith anglefilters correctionPoissondark currentcross sectionsNO2 effective heightNO2 effective temperatureα Angstromwavelengthdead timeO4 correctionresolutiontotalMonte Carlo uncertainty budget> 10 factors taken into accountField measurement campaignsComparison among different algorithms-3-2-10123260 262 264 266 268 270 272 274 276DUdayMuch less noise than Barton's algorithm (2007)...Field measurement campaignsComparison among different algorithms-3-2-10123264.2 264.3 264.4 264.5 264.6 264.7 264.8 264.9DUday... and much smaller dependence on wavelengths misalignments(crosses: hg test misalignments on same scale)Field measurement campaignsOther retrievable quantities00.10.20.30.40.50.60.70.8-100 -50 0 50 100Lpsolar zenith angle-0.4-0.200.20.40.60.8-100 -50 0 50 100Lpsolar zenith angleNew product: degree of linear polarisation of the sky(left: clear sky; right: fog)Field measurement campaignsOther retrievable quantities-20-15-10-505101520291 292 293 294 295 296O4opticaldepth(ratio)dayNew product: oxygen dimer (O2O2) optical depth(too weak absorption by H2O in the blue band)Field measurement campaignsThe Saint-Christophe campaignThe Brewer #066 calibration can be successfully transferred1 Introduction2 Instrumental characterisation3 Updates to the algorithm4 Field measurement campaigns5 Reprocessing of long-term data sets6 Future researchReprocessing of long-term data setsThe stationsMinimum-Amount Langley Extrapolationand Bootstrap Estimation techniquesHerman (2009)Reprocessing of long-term data setsWavelength misalignments-1-0.500.511.52007 2008 2009 2010 2011 2012 2013NO2(DU)dateAthens, Brewer #001Reprocessing of long-term data setsWavelength misalignments-1-0.500.511.52007 2008 2009 2010 2011 2012 2013NO2(DU)dateAthens, Brewer #001Reprocessing of long-term data setsWavelength misalignments-0.0500.050.10.150.20.250.31 1.5 2 2.5 3 3.5 4 4.5 5retrievedNO2(DU)µNO2step 1002step 998reference step (1000)Reprocessing of long-term data setsWavelength misalignments-0.500.511.522.52007 2008 2009 2010 2011 2012 2013NO2(DU)datePiecewise calibrationAthens, Brewer #001Reprocessing of long-term data setsExploratory data analysisstationIQR (DU)new algorithmIQR (DU)old algorithmoverestimationby oldalgorithmSaint-Christophe 0.190.3 1.01.3 340%Hradec Králové 0.30.5 1.31.9 275%Rome 0.280.6 1.21.8 275%Athens 0.30.7 0.81.5 120%Years: 20072013Reprocessing of long-term data setsCorrelation with in situ concentrations0.150.20.250.30.350.40.450.5DU2008 2009 2010 2011 2012 20131020304050607080µgm3datein situ concentrationBrewer VCDAosta, Brewer #066 (monthly averages)Spearman's rs = 0.7 when compared to in situ concentrationsReprocessing of long-term data setsSeasonal cycle00.511.52J F M A M J J A S O N DNO2(DU)monthAosta, Brewer #066temperature inversionsand stagnationincreased photolysisduring summerincreased NO2 lifetimeduring winter (lowertemperatures)increased emissions inwinterReprocessing of long-term data setsWeekly cycle00.511.522.5S M T W T F SNO2(DU)day of weekRome, Brewer #067Significant differences between weekdays and weekendsin all analysed stationsReprocessing of long-term data setsDaily cycle00.20.40.60.816 8 10 12 14 16 18NO2(DU)hour (UT)Aosta, Brewer #066Morning rush hours  No (inverse-)U shapeReprocessing of long-term data setsSpaceborne estimatesmuch morecomparable, nowoverall bias -2.4%low correlationlack of seasonalitycompared to satellites 00.20.40.60.811.22007 2008 2009 2010 2011 2012 2013DUdateBrewerOMISCIAMACHYGOME2aRome, Brewer #067Monthly averages1 Introduction2 Instrumental characterisation3 Updates to the algorithm4 Field measurement campaigns5 Reprocessing of long-term data sets6 Future researchFuture researchAOD retrieval at 440 nm (STSM)more accurate Brewer-satellites comparison (STSM)Ring effectI more accurate zenith sky measurementsstratosphere-troposphere partitioning (ds + zs)Moon measurements (already started)View publication stats

Improvements to the nitrogen dioxide observations by means of the MKIV Brewer spectrophotometer

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Improvements to the nitrogen dioxide observations by means of the MKIV Brewer spectrophotometer

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