Temperature correction for OMI NO2 slant column densities (SCD) [405-465 nm]

Revisiting the temperature correction factor for OMI

1. DOMINO-2: GOME data

fitted in 425-450 nm

1. Reevaluation

1. Reprocessed OMI NO2

SCDs (v2.0) fitted with cross-sections at 220°K, 240°K, 294°K.

1. Non-linear fit to the

nominal temperature correction factors of 220°K, 240°K, 294°K.

Uncertainty Analysis on OMI NO2 SCDs: • Intercomparison between DOMINO-2, DOMINO-3,

and QA4ECV SCDs

• Theory vs Practice (T5.5)

statistics on SCDs

DO

AS

Reprocessed OMI NO2 Slant Columns

DOMINO-3

1. Account for wavelength dependency of OMI slit function.

1. Wavelength

calibration window optimized.

1. Reference spectra

update. 1. Inclusion of

absorption by O2-O2 and H2Oliq.

QA4ECV

1. Account for viewing angle dependency of OMI slit function.

2. Different fitting equation (optical density vs. intensity fitting).

3. Inclusion of intensity offset term (1/I0).

DOMINO-3- QA4ECV SCDs

in agreement within 5%

QA4ECV SCDs reduced by 15%

Methodology

• Selection of 2° x 2° boxes over the Pacific

2°

2°

• AMF variability check

Slant Column Uncertainty: DOMINO-2, DOMINO-3, QA4ECV SCDs

6% lower SCD uncertainty for QA4ECV SCDs

SCD uncertainty =

Fitting uncertainty + Stripiness

Slant Column Uncertainty: DOMINO-2, DOMINO-3, QA4ECV SCDs

6% lower SCD uncertainty for QA4ECV SCDs

SCD uncertainty =

Fitting uncertainty + Stripiness

Theory vs Practice: Uncertainty of the Uncertainty

15%

DOMINO-2

45% 22%

QA4ECV

DOMINO-3

Higher agreement for DOMINO-3 & QA4ECV SCDs

Conclusions

• Revisit on the temperature correction for OMI NO2 SCDs; implementation in DOMINO-3: temperature sensitivity drops from 4.8%/°K to 3.2%/°K.

• Consistency between new DOMINO-3- and QA4ECV- NO2 SCDs within 5%.

• Statistical evaluations suggest NO2 SCD uncertainty reduced by 6%.

• Better match between DOAS-fit- and statistical NO2 SCD uncertainty;

better understanding of the DOAS fitting uncertainty.(∗∗)

T5.5 Slant column QA (evaluate theoretical precision against statistical uncertainty over

reference sector)

(∗∗)

Temperature Correction Factors so far

I.

III.

Boersma et al. [2002] & Bucsela et al. [2013] (405-465 nm):

II.

Boersma et al.[2004] (425-450 nm):

Present Work (425-450 nm)

SP2

DOMINO-2

DOMINO-3

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Simplest approach: Scaled Cross-Sections (X)

240°K– and 294°K- differential X are a scaled version of 220°K- differential X: A as a scaling factor

To = 220 K

A240 = 0.939

A294 = 0.789

Differences between Scaled X: contributor to the ‘DOAS fitting residuals’

min.

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A240 = 0.939 A294 = 0.789

Temperature correction factors, C, are considerably close to scaling factors, A.

C(T) magnitude dominated when #observations is highest

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Wavelength Window

A (240°K) C (240°K) A (294°K) C (294°K)

405 – 465 nm 0.939 0.938 0.789 0.785

425 – 450 nm 0.935 0.773

The different wavelength window

explains ≈ 25%

Good agreement between the scaling factors, especially for lower temperatures

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Underestimation

Overestimation

Figure courtesy of Henk Eskes (KNMI)

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AMF variability

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