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Vital improvements to the retrieval of tropospheric NO2 columns from the Ozone Monitoring Instrument

(1) Eindhoven University of Technology, Eindhoven, The Netherlands (2) Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands

(3) Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium (4) Delft University of Technology, Delft, The Netherlands

J.D. Maasakkers1,2,*, K.F. Boersma1,2, J.E. Williams2, J. van Geffen2, H.J. Eskes2, G.C.M. Vinken1, M. Sneep2, J. de Haan2, F. Hendrick3, M. van Roozendael3 and, J.P. Veefkind2,4

A Introduction D Cloud temperature dependence

Satellite observations of nitrogen dioxide (NO2) are important for monitoring and studying concentrations of nitrogen oxides, but considerable uncertainties on the accuracy and robustness of the retrievals, and their fitness for model evaluation still persist. Here, we present a number of relevant improvements to the slant and vertical NO2 column retrieval algorithm from OMI (first steps to DOMINO v3).

While DOMINO v2 [Boersma et al., 2011] used a TM4 a priori profiles at 3°×2°, we have now coupled our new version 3 retrieval to the TM5 global 3D CTM, which provides a priori profiles with a 1°×1° resolution. As suggested previously by Boersma et al. (2007) and demonstrated by Heckel et al. (2011), the better resolved a priori profile shapes lead to a better understanding of pollution gradients observed from space. Figure C1 shows the difference between modeled tropospheric NO2 columns of TM5 at 3°×2° (left) and 1°×1° (right). Figure C2 shows the difference between OMI tropospheric NO2 columns retrieved with TM5 at 3°×2° and 1°×1°.

R References [Boersma et al., 2007] K. F. Boersma, H. J. Eskes, J. P. Veefkind, E. J. Brinksma, R. J. van der A, M. Sneep, G. H. J. van den Oord, P. F. Levelt, P. Stammes, J. F. Gleason, and E. J. Bucsela (2007), Near-real time retrieval of tropospheric NO2 from OMI, Atmos. Chem. Phys., 7, 2103-2118 [Heckel et al., 2011] A. Heckel, S.-W. Kim, G. J. Frost, A. Richter, M. Trainer, and J.P. Burrows (2011), Influence of low spatial resolution a priori data on tropospheric NO2 satellite retrievals, Atmos. Meas. Tech., 4, 1805-1820 [Boersma et al, 2011] K.F. Boersma, H.J. Eskes, R.J. Dirksen, R.J. van der A, J.P. Veefkind, P. Stammes, V. Huijnen, Q.L. Kleipool, M. Sneep, J. Claas, J. Leitão, A. Richter, Y. Zhou, and D. Brunner (2011), An improved tropospheric NO2 column retrieval algorithm for the Ozone Monitoring Instrument, Atmos. Meas. Tech. Discuss., 4, 2329-2388

B Slant column revision

The OMI cloud retrieval uses the absorption of the O2-O2 collision complex at 477nm to determine the cloud fraction and cloud pressure. This retrieval, assumes a constant mid-latitude summer temperature profile (Tmls) for every measurement. This leads to errors in the assumed O2-O2 density. The bias is most important for measurements with small cloud fractions. Here, we apply a correction (C ) to the O2-O2 slant column that takes into account the actual temperature profile as provided by TM5 (TTM5). Here, m is the altitude-dependent air mass factor (AMF), pTOA the pressure at the top of the atmosphere, and pc the cloud pressure. After the correction, we recalculate the cloud parameters using the LUT from the cloud retrieval with the corrected O2-O2 slant column. The impact on the NO2 tropospheric columns over Europe is shown in figure D.

Fig B1, OMI stratospheric VCDs compared to GOME-2 and SCIAMACHY values over the Pacific

Fig C2, Tropospheric NO2 OMI columns retrieved with TM5 at 1°×1° - retrieved with TM5 at 3°×2° over Europe for 3-8 October 2004

Fig C1, TM5 tropospheric columns at October 8 2004, 1:30PM at 3°×2°(left) and 1°×1° (right)

C Using higher resolution a priori profiles

Fig B2, OMI SCD and accompanying RMS using the improved calibration, as a function of the wavelength window used for the NO2 fit

Fig D, impact on the tropospheric NO2 column for 20-30 October 2004

TTM5 < Tmls ► O2O2 column↑ ► Cloud pressure ↑ ► AMF ↑ ► Retrieved NO2 ↓

A priori NO2↑ ► Lower tropospheric AMF↓ ► Retrieved NO2 ↑

Comparison of stratospheric NO2 columns measured by different instruments shows that OMI retrieves higher values than other satellite instruments (Fig B1) and ground based instruments. This difference in NO2 values is markedly higher than what is expected due to the difference in measurement time. An improved wavelength calibration of the OMI lv1b data reduces the retrieved total slant column density (SCD) by about 13% and the root-mean-square (RMS) of the DOAS fit by about 20%. The RMS can be further reduced by changing the OMI NO2 fit window from the current 405-465 nm to 415-465 nm (Fig B2), which also reduces the SCD. Combining the two changes reduces the SCD over the Pacific Ocean by about 23% and the RMS by about 25%.

Vital improvements to the retrieval of tropospheric NO2 columns from the Ozone Monitoring Instrument

(1) Eindhoven University of Technology, Eindhoven, The Netherlands (2) Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands

(3) Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium (4) Delft University of Technology, Delft, The Netherlands

J.D. Maasakkers1,2,*, K.F. Boersma1,2, J.E. Williams2, J. van Geffen2, H.J. Eskes2, G.C.M. Vinken1, M. Sneep2, J. de Haan2, F. Hendrick3, M. van Roozendael3 and, J.P. Veefkind2,4

A Introduction D Cloud temperature dependence

Satellite observations of nitrogen dioxide (NO2) are important for monitoring and studying concentrations of nitrogen oxides, but considerable uncertainties on the accuracy and robustness of the retrievals, and their fitness for model evaluation still persist. Here, we present a number of relevant improvements to the slant and vertical NO2 column retrieval algorithm from OMI (first steps to DOMINO v3).

While DOMINO v2 [Boersma et al., 2011] used a TM4 a priori profiles at 3°×2°, we have now coupled our new version 3 retrieval to the TM5 global 3D CTM, which provides a priori profiles with a 1°×1° resolution. As suggested previously by Boersma et al. (2007) and demonstrated by Heckel et al. (2011), the better resolved a priori profile shapes lead to a better understanding of pollution gradients observed from space. Figure C1 shows the difference between modeled tropospheric NO2 columns of TM5 at 3°×2° (left) and 1°×1° (right). Figure C2 shows the difference between OMI tropospheric NO2 columns retrieved with TM5 at 3°×2° and 1°×1°.

R References [Boersma et al., 2007] K. F. Boersma, H. J. Eskes, J. P. Veefkind, E. J. Brinksma, R. J. van der A, M. Sneep, G. H. J. van den Oord, P. F. Levelt, P. Stammes, J. F. Gleason, and E. J. Bucsela (2007), Near-real time retrieval of tropospheric NO2 from OMI, Atmos. Chem. Phys., 7, 2103-2118 [Heckel et al., 2011] A. Heckel, S.-W. Kim, G. J. Frost, A. Richter, M. Trainer, and J.P. Burrows (2011), Influence of low spatial resolution a priori data on tropospheric NO2 satellite retrievals, Atmos. Meas. Tech., 4, 1805-1820 [Boersma et al, 2011] K.F. Boersma, H.J. Eskes, R.J. Dirksen, R.J. van der A, J.P. Veefkind, P. Stammes, V. Huijnen, Q.L. Kleipool, M. Sneep, J. Claas, J. Leitão, A. Richter, Y. Zhou, and D. Brunner (2011), An improved tropospheric NO2 column retrieval algorithm for the Ozone Monitoring Instrument, Atmos. Meas. Tech. Discuss., 4, 2329-2388

B Slant column revision

The OMI cloud retrieval uses the absorption of the O2-O2 collision complex at 477nm to determine the cloud fraction and cloud pressure. This retrieval, assumes a constant mid-latitude summer temperature profile (Tmls) for every measurement. This leads to errors in the assumed O2-O2 density. The bias is most important for measurements with small cloud fractions. Here, we apply a correction (C ) to the O2-O2 slant column that takes into account the actual temperature profile as provided by TM5 (TTM5). Here, m is the altitude-dependent air mass factor (AMF), pTOA the pressure at the top of the atmosphere, and pc the cloud pressure. After the correction, we recalculate the cloud parameters using the LUT from the cloud retrieval with the corrected O2-O2 slant column. The impact on the NO2 tropospheric columns over Europe is shown in figure D.

Fig B1, OMI stratospheric VCDs compared to GOME-2 and SCIAMACHY values over the Pacific

Fig C2, Tropospheric NO2 OMI columns retrieved with TM5 at 1°×1° - retrieved with TM5 at 3°×2° over Europe for 3-8 October 2004

Fig C1, TM5 tropospheric columns at October 8 2004, 1:30PM at 3°×2°(left) and 1°×1° (right)

C Using higher resolution a priori profiles

Fig B2, OMI SCD and accompanying RMS using the improved calibration, as a function of the wavelength window used for the NO2 fit

Fig D, impact on the tropospheric NO2 column for 20-30 October 2004

TTM5 < Tmls ► O2O2 column↑ ► Cloud pressure ↑ ► AMF ↑ ► Retrieved NO2 ↓

A priori NO2↑ ► Lower tropospheric AMF↓ ► Retrieved NO2 ↑

Comparison of stratospheric NO2 columns measured by different instruments shows that OMI retrieves higher values than other satellite instruments (Fig B1) and ground based instruments. This difference in NO2 values is markedly higher than what is expected due to the difference in measurement time. An improved wavelength calibration of the OMI lv1b data reduces the retrieved total slant column density (SCD) by about 13% and the root-mean-square (RMS) of the DOAS fit by about 20%. The RMS can be further reduced by changing the OMI NO2 fit window from the current 405-465 nm to 415-465 nm (Fig B2), which also reduces the SCD. Combining the two changes reduces the SCD over the Pacific Ocean by about 23% and the RMS by about 25%.

Vital improvements to the retrieval of tropospheric NO2 columns from the Ozone Monitoring Instrument

(1) Eindhoven University of Technology, Eindhoven, The Netherlands (2) Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands

(3) Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium (4) Delft University of Technology, Delft, The Netherlands

J.D. Maasakkers1,2,*, K.F. Boersma1,2, J.E. Williams2, J. van Geffen2, H.J. Eskes2, G.C.M. Vinken1, M. Sneep2, J. de Haan2, F. Hendrick3, M. van Roozendael3 and, J.P. Veefkind2,4

A Introduction D Cloud temperature dependence

Satellite observations of nitrogen dioxide (NO2) are important for monitoring and studying concentrations of nitrogen oxides, but considerable uncertainties on the accuracy and robustness of the retrievals, and their fitness for model evaluation still persist. Here, we present a number of relevant improvements to the slant and vertical NO2 column retrieval algorithm from OMI (first steps to DOMINO v3).

While DOMINO v2 [Boersma et al., 2011] used a TM4 a priori profiles at 3°×2°, we have now coupled our new version 3 retrieval to the TM5 global 3D CTM, which provides a priori profiles with a 1°×1° resolution. As suggested previously by Boersma et al. (2007) and demonstrated by Heckel et al. (2011), the better resolved a priori profile shapes lead to a better understanding of pollution gradients observed from space. Figure C1 shows the difference between modeled tropospheric NO2 columns of TM5 at 3°×2° (left) and 1°×1° (right). Figure C2 shows the difference between OMI tropospheric NO2 columns retrieved with TM5 at 3°×2° and 1°×1°.

R References [Boersma et al., 2007] K. F. Boersma, H. J. Eskes, J. P. Veefkind, E. J. Brinksma, R. J. van der A, M. Sneep, G. H. J. van den Oord, P. F. Levelt, P. Stammes, J. F. Gleason, and E. J. Bucsela (2007), Near-real time retrieval of tropospheric NO2 from OMI, Atmos. Chem. Phys., 7, 2103-2118 [Heckel et al., 2011] A. Heckel, S.-W. Kim, G. J. Frost, A. Richter, M. Trainer, and J.P. Burrows (2011), Influence of low spatial resolution a priori data on tropospheric NO2 satellite retrievals, Atmos. Meas. Tech., 4, 1805-1820 [Boersma et al, 2011] K.F. Boersma, H.J. Eskes, R.J. Dirksen, R.J. van der A, J.P. Veefkind, P. Stammes, V. Huijnen, Q.L. Kleipool, M. Sneep, J. Claas, J. Leitão, A. Richter, Y. Zhou, and D. Brunner (2011), An improved tropospheric NO2 column retrieval algorithm for the Ozone Monitoring Instrument, Atmos. Meas. Tech. Discuss., 4, 2329-2388

B Slant column revision

The OMI cloud retrieval uses the absorption of the O2-O2 collision complex at 477nm to determine the cloud fraction and cloud pressure. This retrieval, assumes a constant mid-latitude summer temperature profile (Tmls) for every measurement. This leads to errors in the assumed O2-O2 density. The bias is most important for measurements with small cloud fractions. Here, we apply a correction (C ) to the O2-O2 slant column that takes into account the actual temperature profile as provided by TM5 (TTM5). Here, m is the altitude-dependent air mass factor (AMF), pTOA the pressure at the top of the atmosphere, and pc the cloud pressure. After the correction, we recalculate the cloud parameters using the LUT from the cloud retrieval with the corrected O2-O2 slant column. The impact on the NO2 tropospheric columns over Europe is shown in figure D.

Fig B1, OMI stratospheric VCDs compared to GOME-2 and SCIAMACHY values over the Pacific

Fig C2, Tropospheric NO2 OMI columns retrieved with TM5 at 1°×1° - retrieved with TM5 at 3°×2° over Europe for 3-8 October 2004

Fig C1, TM5 tropospheric columns at October 8 2004, 1:30PM at 3°×2°(left) and 1°×1° (right)

C Using higher resolution a priori profiles

Fig B2, OMI SCD and accompanying RMS using the improved calibration, as a function of the wavelength window used for the NO2 fit

Fig D, impact on the tropospheric NO2 column for 20-30 October 2004

TTM5 < Tmls ► O2O2 column↑ ► Cloud pressure ↑ ► AMF ↑ ► Retrieved NO2 ↓

A priori NO2↑ ► Lower tropospheric AMF↓ ► Retrieved NO2 ↑

Comparison of stratospheric NO2 columns measured by different instruments shows that OMI retrieves higher values than other satellite instruments (Fig B1) and ground based instruments. This difference in NO2 values is markedly higher than what is expected due to the difference in measurement time. An improved wavelength calibration of the OMI lv1b data reduces the retrieved total slant column density (SCD) by about 13% and the root-mean-square (RMS) of the DOAS fit by about 20%. The RMS can be further reduced by changing the OMI NO2 fit window from the current 405-465 nm to 415-465 nm (Fig B2), which also reduces the SCD. Combining the two changes reduces the SCD over the Pacific Ocean by about 23% and the RMS by about 25%.

Bram  Maasakkers