global free t ropospheric no 2 abundances derived using a cloud slicing technique from aura omi

Global free tropospheric NO2 Abundances Derived using a Cloud Slicing Technique

from Aura OMI

S. Choi, J. Joiner, Y. Choi, B. N. Duncan, and E. J. Bucsela

OMI Science Team Meeting2014. 3. 13.

2OMI Science Team Meeting 2014

Outline

Background

Cloud slicing technique Evaluation of cloud slicing technique in conjunction

with INTEX-B data

Global seasonal climatology of free tropospheric NO2

Profile analysis Stratospheric column NO2

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Free Tropospheric NO2

Atmospheric NO2

– Produced by combustion, lightning, and in soil– Affects air quality - affects ozone production and criteria pollutant itself

Indirect radiative impacts in troposphere– Ozone has largest warming effect in upper-troposphere– Impacts methane concentrations

Tropospheric vertical column densities (VCD) of NO2 are available from satellites (GOME, OMI, SCIAMACHY, GOME-2)– No profile information

A few types of free-tropospheric NO2 measurements available– Aircraft in situ measurements, MAX-DOAS, NO2 sondes, etc.

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Cloud Slicing Technique

Utilize above-cloud NO2 column (where CRF > 0.9)– Good quality column measurements as clouds provide bright

surface– Usually neglected in the view of surface pollution

Data obtained– Free tropospheric NO2 volume mixing ratio (VMR)

– Stratospheric column NO2

Independent of– A priori information– Prescribed stratospheric column estimate

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Ground

Top of Atmosphere (TOA)

Clou

d sc

ene

pres

sure

(hPa

)

NO2 VCD above the clouds

Cloud scenepressure

NO2 VMR

= *kB*g/Rair

dVCDdP

ΔP

ΔVCD

Measurement at Cloudy Scenes Observed Column vs Pressure

Ground

TOA

~1013

0

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The slope between NO2 VCD and cloud pressure is proportional to NO2 volume mixing ratio (VMR)

Ground


Clou

d sc

ene

pres

sure

(hPa

)

NO2 VCD above the clouds

Cloud scenepressure

NO2 VMR

= *kB*g/Rair

dVCDdP

ΔP

ΔVCD


Ground

TOA

~1013

0

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Extended linear fit to the tropopause gives an estimate of stratospheric column

Ground


Cloud scenepressure

ΔP

ΔVCD


Ground

TOA

~1013

0

TropopausePressure

Strat NO2 VCD (above-tropopause column)

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Assumptions– Uniform NO2 VMR in the sampling pressure ranges– No stratospheric variation in the sampling

spatial/temporal ranges (6ox 8o, calculated per orbit)

Limitations– Represent cloudy conditions only– Magnitudes only as accurate as above-cloud NO2 VCD

• SCD may be overestimated up to ~30% in current study

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Comparison with INTEX-B Data

A case near Houston, TX Reasonable agreement with positive bias (~35%)

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Comparison with INTEX-B Data

A case over northeast Pacific Reasonable agreement with positive bias (~35%)

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Evaluation of Cloud Slicing NO2 VMR

All available matchups No correlation Similar magnitude with positive bias3/13/2014


Evaluation of Cloud Slicing NO2 VMR

INTEX-B VMR standard error < 5 pptv Weak correlation and positive bias Reasonable agreement despite the intrinsic limits:

– Poor collocation, small scale features, clear/cloudy conditions3/13/2014


Global Seasonal Climatology

Global seasonal free-tropospheric NO2 climatology– Take advantage of high spatial/temporal coverage of

satellite measurements– Concentrate on spatial and seasonal patterns

Large volume of data required for reasonable results– 3-year OMI data accumulated (2005-2007)– Coarse resolution (6o latitude x 8o longitude)

Distinct patterns in the free tropospheric VMR– Independent source of data to study free troposphere

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3/13/2014 OMNO2B



Different spatial patterns from tropospheric column

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Appears to be anthropogenic contributions (uplifted pollution & outflow)

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Appears to be lightning contributions(dominates during summer months)

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Appears to be anthropogenic contributions (uplifted pollution & outflow)

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Appears to be lightning contributions(dominates during summer months)

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Profile Analysis

Coarse profile analysis (~100 hPa resolution)

Requires even more data with significant cloud pressure variability

Two example cases– East Asia and its outflow for anthropogenic NO2

– Tropical oceans of NH and SH for lightning NO2

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Profile Analysis

High NO2 at 600-800 hPa

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Profile Analysis

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Profile Analysis

High NO2 above 500 hPa in summer

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Estimates of Stratospheric Column NO2

Estimate from cloud slicing agrees very well with independently derived estimates from OMNO2B – provides further confidence in derived free-tropopsheric VMRs3/13/2014


Conclusions Free tropospheric NO2 VMR derived using cloud slicing

Global seasonal climatology shows anthropogenic and natural (lightning) features of free tropospheric NO2, independent of the tropospheric column

Profile analysis shows uplifted anthropogenic NO2 in the middle troposphere as well as lightning NO2 in the upper troposphere

Estimated stratospheric column NO2 agrees well with independent stratospheric NO2 estimates

Expect collaborations with free tropospheric NO2 measurements including NO2 sondes

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Thank you

S. Choi et al.: Global free tropospheric NO2 Abundances Derived using a Cloud Slicing Technique from Aura OMI, Atmos. Chem. Phys. Discuss., 2013


Backup slides

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Detail/Data Screening Criteria

Use slant column density (OMNO2A) and geometric AMF

Cloud radiance fraction > 0.9 Aerosol index < 1.0 No snow/ice surface Solar zenith angle < 80 degree Gradient of NO2 VMR < 0.33 pptv / hpa (profiles from

GMI model or INTEX-B measurements)

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Example of Calculated NO2 Climatology

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Free Trop. NO2 VMR (OMI vs GMI)OMI GMI

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Tropospheric Column NO2 (OMI vs GMI)OMI GMI

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global free t ropospheric no 2 abundances derived using a cloud slicing technique from aura omi

Documents

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cloud no2 vcdscd

cloud pressure

cloud slicing techniqueutilize

no2 sondes

intexb dataa case

types of free

positive biasreaso