Study on NOx lifetime in chemistry transport model

Ran Yin

Motivation• Nitrogen oxides plays an important role in tropospheric chemistry• Discrepancy between the model simulation and satellite-retrieved troposp

heric NO2 columns: Why??• How to optimize emission inventory using space-borne column: the NOx lif

etime is a critical parameter in the inversion, especially in higher resolution.

simulated NO2 column (1015 moles/cm2)

OMI NO2 column (1015 moles/cm2)

Motivation (con’t)• GOME2 observes up to 100% higher than OMI. Can we explain the obser

ved decrease in NO2 column by a diurnal cycle of NOx lifetime?

GOME2 OMI

(1015 moles/cm2)

Background InformationHow is NO2 column measured by satellite?

SOLAR BACKSCATTER MEASUREMENTS

Scattering by Earth surface and by atmosphere

NO2 : wavelength region 420-450 nm

Top-down Information from Satellite:

GOME 1995-2003

SCIAMACHY 2002-present

OMI 2004-present

GOME-2 2006-present

Solar Io

Backscatteredintensity IB

Albedo A

∑= − seIAIBτλλλ )()()( 0

Background Information (con’t)

Emission

NO NO2

HNO3

lifetime

NITROGEN OXIDES (NOx)

Tropospheric NO2 column ~ ENOx

NOx = NO + NO2

Map Surface NOMap Surface NOx x EmissionsEmissions

Wind smears the local relationship between column and emission

Do we need to worry about the transport between grid boxes?

Method

chemistryτ transportτ

dΩdτ

=E + P−L−D + Fin −Fouτ

E: emission P: production L: loss D: deposition Fin: Flux-in Fout: Flux-out

Chemistry: principle daytime removal path for NOx is OH + NO2 + M → HNO3+ M

Comparison between two kind of lifetime:

Loss by reaction and deposition

Loss by horizontal transport to other gridbox

Simplify Eq.1:

Eq.1

dΩdτ

=E −kΩ + Fin −Fouτ

Solve continuity equation:

emission chemistry transport flux

= k-1

Using a regional chemistry transport model (REAM) :

Result: Chemistry lifetime• In every time-step (1 hr):

)/1exp()/1exp(1( chemchembeforechemchemchemafter E τττ −⋅Ω+−−⋅⋅=Ω −−

lifet

ime

[hou

r]

[hour]

determined by oxidation rate and dry deposition

OH depletion

dΩdτ

=E −kΩ

100 % difference between GOME2 overpass and OMI overpass

Result: Integrated Lifetime• Set Fin = 0, between each time-step

Ωn+1 = E ⋅τ int egrated ⋅(1− exp(−1 / τ int egrated ) + Ωn ⋅exp(−1 / τ int egrated )

lifet

ime

[hou

r]

[hour]

dΩdτ

=E −kΩ −Fouτ

much smaller difference, insufficient to explain the difference between two satellite

Result: Transport lifetime

)/1/1/(1 int chemegratedtransport τττ −=

lifet

ime

[hou

r]

[hour]

Result: Comparison between two lifetime

Red region: chemistry lifetime > transport time

GOME2 overpass OMI overpass nighttime

Conclusion• By comparison between chemistry lifetime and transpo

rt lifetime, the model with a horizontal resolution of 36 km is sensitive to NO2 signal in summer daytime

• Although chemical loss rate much higher at OMI overpass, the discrepancy between GOME2 and OMI can not be explained by the overall lifetime of NOx at different time of the day