Improvements to the nitrogen dioxide observations by means ... › bitstream › 20.500... · Improvements to the nitrogen dioxide observations by means of the MKIV Brewer spectrophotometer

Improvements to the nitrogen dioxide observations by

means of the MKIV Brewer spectrophotometer

H. 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 2

M. Stanek 7 J. P. Burrows 8 A. Richter 8 A. Hilboll 8

1ARPA Valle d'Aosta, 2Sapienza Università di Roma, 3IOS, 4AEMET, 5Academy of Athens,6EEWRC, 7�HMÚ and 8University of Bremen

14th WMO-GAW Brewer users group meetingTenerife, March 2014

1 Introduction

2 Instrumental characterisation

3 Updates to the algorithm

4 Field measurement campaigns

5 Reprocessing of long-term data sets

6 Future research

IntroductionMeasurements with Brewer spectrophotometers

MKIV

426 � 453 nm (visible)

original algorithm: Kerr (1989)

updates (not implemented):Barton (2007)

MKIII

349 � 363 (UV-A)

Cede et al. (2006)


What's wrong with NO2 measurements using the Brewer?

overestimations (>200%) with thecurrent algorithm

I other ground-based instrumentsI satellite radiometers

random deviationsI due to interferences (O4, H2O, Ring)I sensitivity to instrumental settings

(e.g. wavelength misalignments)

noiseI depends on both the algorithm and

used wavelengths

no calibration service for NO2


Open questions

can 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?


What was done

1 mathematical framework and numericalsimulations

I accurate characterisation of Brewer#066

I parameterisation of all in�uencingfactors

2 updated spectroscopic dataset

3 new (polarised) AMFs for ZS geometry

4 variable-Langley calibration (Izaña)

5 Montecarlo uncertainty budget

6 reprocessing of 4 long-term series

1 Introduction





6 Future research

Instrumental characterisation

Fundamental to reveal the weak signal of NO2

dispersion

�neutral density� �lters

temperature dependence

etc.

[Diémoz et al., 2011, Brewer Meeting, Beijing]

1 Introduction





6 Future research

Updates to the algorithmNoise reduction

~γ ·−→βR ≡ 0

~γ · −−→αO3 ≡ 0

~γ ·−→δA ≡ 0

~γ ·~1 ≡ 0

~γ ‖ αNO2

6 slits =more degrees of freedom =

noise reduction

Updates to the algorithmInterfering factors

Considered factors

noise

oxygen dimer (O4)

water vapor (H2O)

Ring e�ect

sensitivity to NO2

e�ective temperature

wavelengthmisalignments 0

0.01

0.02

0.03

0.04

0.05

400 420 440 460 480 500

opticaldepth

wavelength (nm)

totalO3

NO2H2OO4

CHOCHO

Updates to the algorithmIncreasing the DOF

0

1

2

3

4

5

0 500 1000 1500 2000 2500 3000

noise

(DU)

micrometer steps

For every in�uencing factor a diagram was assessedand the optimal grating positions (i.e. wavelengths) were found

Updates to the algorithmJump scans

420 430 440 450 460 470 480

wavelength (nm)

a)

b)

c)

11 slitsO4 and H2O included in the retrieval

Updates to the algorithm

Further updates

all 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 coe�cients)I O4 - Hermans 2003 (previously neglected)I H2O - Hitran + Py4CATS (previously neglected)

I0-e�ect taken into account

new weighting factors

polarised AMFs for ZS geometry (SCIATRAN, full-spherical)

Updates to the algorithmRadiative transfer calculations

0.9

1

1.1

1.2

1.3

1.4

1.5

0 10 20 30 40 50 60 70 80

DU

solar zenith angle (deg)

[Diémoz et al., 2013, SPIE, Dresden]

1 Introduction





6 Future research

Field measurement campaignsThe Izaña campaign

38 days of measurements

5 days removed because offog/rain

no relevant contamination bySaharan dust on ratios

2 days for initial checks

16 days for direct-sunmeasurements (3 steps)

15 days for zenith-skymeasurements (3 steps and 2polarizations)

5 days for O3 and O4 direct-sunmeasurements

Field measurement campaignsLangley in varying conditions

Improving the Langley: linear changes with time

y(t)

µ(t)=a

1

µ(t)+ b(t)

=a1

µ(t)− δ − ξt

(1)


(a δ ξ

)T= A

†(

y1µ1

... ynµn

)T(2)


-0.1

0

0.1

0.2

0.3

0.4

8 10 12 14 16 18

NO2columndensity

(DU)

time(hours)

Izana clim. (AM)Izana clim. (PM)

linear �t

site reference daytime increasing rate (1013 molec

cm2 h)

Zugspitze/Garmisch Sussmann et al. (2005) 5�15Izaña Gil et al. (2008) 6

Paci�c Ocean Peters et al. (2012) 8.7±0.5Izaña present study 7.0�12.5


-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-40 -30 -20 -10 0 10 20 30 40

DU

airmass

directzenith (parallel)

zenith (perpendicular)

Measurements using the three di�erent geometries are equivalentwithin their respective uncertainties

(airmass < 0 morning; > 0 afternoon)


0.06

0.07

0.08

0.09

0.1

0.11

0.12

0.13

0.14

0.15

0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15

Brewer

(DU)

NDACC (DU)

�ty=x

The Brewer does not overestimate anymore

Field measurement campaignsComparison among di�erent algorithms

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

260 262 264 266 268 270 272 274 276

DU

day

Izaña (2012) � Pink: Kerr's algorithm;green: �lters and Rayleigh updates; blue: new algorithm.

Field measurement campaignsUncertainty budget

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

10 20 30 40 50 60 70 80

NO2uncertainty

(DU)

solar zenith angle

�lters correctionPoisson

dark currentcross sections

NO2 e�ective heightNO2 e�ective temperature

α Angstromwavelengthdead time

O4 correctionresolution

total

Monte Carlo uncertainty budget> 10 factors taken into account


-3

-2

-1

0

1

2

3

260 262 264 266 268 270 272 274 276

DU

day

Much less noise than Barton's algorithm (2007)...


-3

-2

-1

0

1

2

3

264.2 264.3 264.4 264.5 264.6 264.7 264.8 264.9

DU

day

... and much smaller dependence on wavelengths misalignments(crosses: hg test misalignments on same scale)

Field measurement campaignsOther retrievable quantities

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-100 -50 0 50 100

Lp

solar zenith angle

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-100 -50 0 50 100

Lp

solar zenith angle

New product: degree of linear polarisation of the sky(left: clear sky; right: fog)

Field measurement campaignsOther retrievable quantities

-20

-15

-10

-5

0

5

10

15

20

291 292 293 294 295 296

O4opticaldepth

(ratio)

day

New product: oxygen dimer (O2�O2) optical depth(too weak absorption by H2O in the blue band)

Field measurement campaignsThe Saint-Christophe campaign

The Brewer #066 calibration can be successfully transferred

1 Introduction





6 Future research

Reprocessing of long-term data setsThe stations

�Minimum-Amount Langley Extrapolation�and �Bootstrap Estimation� techniques

Herman (2009)

Reprocessing of long-term data setsWavelength misalignments

-1

-0.5

0

0.5

1

1.5

2007 2008 2009 2010 2011 2012 2013

NO2(D

U)

date

Athens, Brewer #001


-1

-0.5

0

0.5

1

1.5

2007 2008 2009 2010 2011 2012 2013

NO2(D

U)

date

Athens, Brewer #001


-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

1 1.5 2 2.5 3 3.5 4 4.5 5

retrievedNO2(D

U)

µNO2

step 1002step 998

reference step (1000)


-0.5

0

0.5

1

1.5

2

2.5

2007 2008 2009 2010 2011 2012 2013

NO2(D

U)

date

�Piecewise� calibrationAthens, Brewer #001

Reprocessing of long-term data setsExploratory data analysis

stationIQR (DU)

new algorithmIQR (DU)

old algorithm

overestimationby old

algorithm

Saint-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�2013

Reprocessing of long-term data setsCorrelation with in situ concentrations

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

DU

2008 2009 2010 2011 2012 201310

20

30

40

50

60

70

80

µg

m3

date

in situ concentrationBrewer VCD

Aosta, Brewer #066 (monthly averages)Spearman's rs = 0.7 when compared to in situ concentrations

Reprocessing of long-term data setsSeasonal cycle

0

0.5

1

1.5

2

J F M A M J J A S O N D

NO2(D

U)

month

Aosta, Brewer #066

temperature inversionsand stagnation

increased photolysisduring summer

increased NO2 lifetimeduring winter (lowertemperatures)

increased emissions inwinter

Reprocessing of long-term data setsWeekly cycle

0

0.5

1

1.5

2

2.5

S M T W T F S

NO2(D

U)

day of week

Rome, Brewer #067Signi�cant di�erences between weekdays and weekends

in all analysed stations

Reprocessing of long-term data setsDaily cycle

0

0.2

0.4

0.6

0.8

1

6 8 10 12 14 16 18

NO2(D

U)

hour (UT)

Aosta, Brewer #066Morning rush hours � No (inverse-)U shape

Reprocessing of long-term data setsSpaceborne estimates

much morecomparable, nowoverall bias -2.4%

low correlation

lack of seasonalitycompared to satellites 0

0.2

0.4

0.6

0.8

1

1.2

2007 2008 2009 2010 2011 2012 2013

DU

date

BrewerOMI

SCIAMACHYGOME2a

Rome, Brewer #067Monthly averages

1 Introduction





6 Future research

Future research

AOD retrieval at 440 nm (STSM)

more accurate Brewer-satellites comparison (STSM)

Ring e�ectI more accurate zenith sky measurements

stratosphere-troposphere partitioning (ds + zs)

Moon measurements (already started)

View publication statsView publication stats

https://www.researchgate.net/publication/310000587

Documents

Improvements to the nitrogen dioxide observations by means ... › bitstream › 20.500... · Improvements to the nitrogen dioxide observations by means of the MKIV Brewer spectrophotometer