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Cross-hemispheric transport of central African biomass burning pollutants: implications for downwind ozone production

Real, E. und Orlandi, E. und Law, K. und Fierli, F. und Josset, D. und Cairo, F. und Schlager, H. und Borrmann, S. und Kunkel, D. und Volk, M. und McQuaid, J. und Stewart, D. und Lee, J. und Lewis, A. und Hopkins, J.R. und Ravegnani, F. und Ulanovsky, A. und Liousse, C. (2010) Cross-hemispheric transport of central African biomass burning pollutants: implications for downwind ozone production. Atmospheric Chemistry and Physics, 10, Seiten 3027-3046.

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Offizielle URL: http://www.atmos-chem-phys.net/10/3027/2010/

Kurzfassung

Pollutant plumes with enhanced concentrations of trace gases and aerosols were observed over the southern coast of West Africa during August 2006 as part of the AMMA wet season field campaign. Plumes were observed both in the mid and upper troposphere. In this study we examined the origin of these pollutant plumes, and their potential to photochemically produce ozone (O3) downwind over the Atlantic Ocean. Their possible contribution to the Atlantic O3 maximum is also discussed. Runs using the BOLAM mesoscale model including biomass burning carbon monoxide (CO) tracers were used to confirm an origin from central African biomass burning fires. The plumes measured in the mid troposphere (MT) had significantly higher pollutant concentrations over West Africa compared to the upper tropospheric (UT) plume. The mesoscale model reproduces these differences and the two different pathways for the plumes at different altitudes: transport to the northeast of the fire region, moist convective uplift and transport to West Africa for the upper tropospheric plume versus north-west transport over the Gulf of Guinea for the mid-tropospheric plume. Lower concentrations in the upper troposphere are mainly due to enhanced mixing during upward transport. Model simulations suggest that MT and UT plumes are 16 and 14 days old respectively when measured over West Africa. The ratio of tracer concentrations at 600 hPa and 250 hPa was estimated for 14�15 August in the region of the observed plumes and compares well with the same ratio derived from observed carbon dioxide (CO2) enhancements in both plumes. It is estimated that, for the period 1�15 August, the ratio of Biomass Burning (BB) tracer concentration transported in the UT to the ones transported in the MT is 0.6 over West Africa and the equatorial South Atlantic. Runs using a photochemical trajectory model, CiTTy- CAT, initialized with the observations, were used to estimate in-situ net photochemical O3 production rates in these plumes during transport downwind of West Africa. The mid-troposphere plume spreads over altitude between 1.5 and 6 km over the Atlantic Ocean. Even though the plume was old, it was still very photochemically active (mean net O3 production rates over 10 days of 2.6 ppbv/day and up to 7 ppbv/day during the first days) above 3 km especially during the first few days of transport westward. It is also shown that the impact of high aerosol loads in the MT plume on photolysis rates serves to delay the peak in modelled O3 concentrations. These results suggest that a significant fraction of enhanced O3 in mid-troposphere over the Atlantic comes from BB sources during the summer monsoon period. According to simulated occurrence of such transport, BB may be the main source for O3 enhancement in the equatorial south Atlantic MT, at least in August 2006. The upper tropospheric plume was also still photochemically active, although mean net O3 production rates were slower (1.3 ppbv/day). The results suggest that, whilst the transport of BB pollutants to the UT is variable (as shown by the mesoscale model simulations), pollution from biom ss burning can make an important contribution to additional photochemical production of O3 in addition to other important sources such as nitrogen oxides (NOx) from lightning.

Dokumentart:Zeitschriftenbeitrag
Titel:Cross-hemispheric transport of central African biomass burning pollutants: implications for downwind ozone production
Autoren:
AutorenInstitution oder E-Mail-Adresse der Autoren
Real, E.Univ. Pierre et Marie Curie, Paris, F
Orlandi, E.CNR, Bologna, I
Law, K.Univ. Pierre et Marie Curie, Paris, F
Fierli, F.CNR, Bologna, I
Josset, D.Univ. Pierre et Marie Curie, Paris, F
Cairo, F.Istit. per la Scienza dell'Atmos. et del clima, Roma, I
Schlager, H.DLR
Borrmann, S.Univ. of Mainz, Mainz
Kunkel, D.MPIC
Volk, M.J. W. Goethe-Univ. Frankfurt am Main
McQuaid, J.Univ. of Leeds, Leeds, UK
Stewart, D.Univ. of Reading, Reading, UK
Lee, J.Univ. of York, York, UK
Lewis, A.Univ. of York, York, UK
Hopkins, J.R.Univ. of York, York, UK
Ravegnani, F.CNR, Bologna, I
Ulanovsky, A.CAO, Moscow, R
Liousse, C.Univ. de Toulouse, F
Datum:2010
Erschienen in:Atmospheric Chemistry and Physics
Referierte Publikation:Ja
In Open Access:Ja
In SCOPUS:Ja
In ISI Web of Science:Ja
Band:10
Seitenbereich:Seiten 3027-3046
Status:veröffentlicht
Stichwörter:West Africa, biomass burning
HGF - Forschungsbereich:Verkehr und Weltraum (alt)
HGF - Programm:Weltraum (alt)
HGF - Programmthema:W EO - Erdbeobachtung
DLR - Schwerpunkt:Weltraum
DLR - Forschungsgebiet:W EO - Erdbeobachtung
DLR - Teilgebiet (Projekt, Vorhaben):W - Vorhaben Atmosphären- und Klimaforschung (alt)
Standort: Oberpfaffenhofen
Institute & Einrichtungen:Institut für Physik der Atmosphäre > Atmosphärische Spurenstoffe
Hinterlegt von: Yasemin Yilmaz
Hinterlegt am:15 Dez 2009 14:47
Letzte Änderung:12 Dez 2013 20:49

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