Evidence of the impact of deep convection on reactive Volatile Organic Compounds in the upper tropical troposphere during the AMMA experiment in West Africa

Bechara, J.; Borbon, A.; Jambert, Corinne; Colomb, A.; Perros, P.

doi:10.5194/acp-10-10321-2010

Cited by 25 publications

(40 citation statements)

References 46 publications

(40 reference statements)

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“…Using aircraft measurements performed in the framework of the African Monsoon Multidisciplinary Analyses (AMMA) project, showed clear signatures of convective uplift of CO and aerosols into the tropical tropopause layer (TTL). Results from Bechara et al (2010) also pointed to convection as an explanation for observed enhancements of VOCs in the UT over West Africa. Moreover, Sauvage et al (2007b, c) and Barret et al (2010) demonstrated that convection leads to production of important amounts of NO x from lightning in the UT which subsequently leads to O 3 production downwind.…”

Section: Introductionmentioning

confidence: 82%

Emission sources contributing to tropospheric ozone over Equatorial Africa during the summer monsoon

et al. 2011

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Abstract.A global chemistry-climate model LMDz INCA is used to investigate the contribution of African and Asian emissions to tropospheric ozone over Central and West Africa during the summer monsoon. The model results show that ozone in this region is most sensitive to lightning NO x and to Central African biomass burning emissions. However, other emission categories also contribute significantly to regional ozone. The maximum ozone changes due to lightning NO x occur in the upper troposphere between 400 hPa and 200 hPa over West Africa and downwind over the Atlantic Ocean. Biomass burning emissions mainly influence ozone in the lower and middle troposphere over Central Africa, and downwind due to westward transport. Biogenic emissions of volatile organic compounds, which can be uplifted from the lower troposphere to higher altitudes by the deep convection that occurs over West Africa during the monsoon season, lead to maximum ozone changes in the lower stratosphere region. Soil NO x emissions over the Sahel region make a significant contribution to ozone in the lower troposphere. In addition, convective uplift of these emissions and subsequent ozone production are also an important source of ozone in the upper troposphere over West Africa. Concerning AfricanCorrespondence to: I. Bouarar (idir.bouarar@latmos.ipsl.fr) anthropogenic emissions, they only make a small contribution to ozone compared to the other emission categories. The model results indicate that most ozone changes due to African emissions occur downwind, especially over the Atlantic Ocean, far from the emission regions. The import of Asian emissions also makes a considerable contribution to ozone concentrations above 150 hPa and has to be taken into account in studies of the ozone budget over Africa. Using IPCC AR5 (Intergovernmental Panel on Climate Change; Fifth Assessment Report) estimates of anthropogenic emissions for 2030 over Africa and Asia, model calculations show larger changes in ozone over Africa due to growth in Asian emissions compared to African emissions over the next 20 yr.

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Section: Introductionmentioning

confidence: 82%

Emission sources contributing to tropospheric ozone over Equatorial Africa during the summer monsoon

et al. 2011

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“…3.2 and 3.3). In addition, Bechara et al (2010) observed O 3 mixing ratios in the range of 45 nmol mol −1 within the fresh MCS outflow during AMMA compared to 60 nmol mol −1 outside. As the MCS outflow ages, the O 3 composition in the MCS outflow may be affected both by photochemical O 3 production/destruction of uplifted precursors and mixing with the ambient air (Chatfield and Delany, 1990).…”

Section: Production Destruction or Mixing Of O 3 In The Mcs Outflow?mentioning

confidence: 93%

“…The AMMA SOP-2a2 campaign, carried out from 25 July to 31 August 2006, involved not only the German Falcon-20 and Russian M55 Geophysica research aircraft based in Ouagadougou, but also the French Falcon-20 and ATR-42 aircraft, and the British Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 aircraft, all based further northeast in Niamey (13.5 • N, 2.1 • E) in Niger Ancellet et al, 2009;Saunois et al, 2009;Bechara et al, 2010;Law et al, 2010;Real et al, 2010;Reeves et al, 2010). Further downstream, in the Cape Verde region off the coast of West Africa, the NASA-AMMA program (NAMMA) examined the interaction between African Easterly waves (AEW) and the Saharan air layer (SAL) and their role in tropical cyclogenesis (Jenkins et al, 2008;Zipser et al, 2009;Cifelli et al, 2010).…”

Section: The Amma Sop-2a2 Campaignmentioning

confidence: 99%

“…One of the key issues was to investigate the largest mesoscale convective systems (MCS) (Houze, 1993(Houze, , 2004 and their linkage to the WAM variability. The chemical composition of the middle and upper troposphere connected to these deep convective events and their impact on the ozone budget and its precursors over West Africa was a further objective of interest (Ancellet et al, 2009;Bechara et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Mesoscale convective systems observed during AMMA and their impact on the NO<sub>x</sub> and O<sub>3</sub> budget over West Africa

et al. 2011

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Abstract. During the "African Monsoon MultidisciplinaryAnalysis" (AMMA) field phase in August 2006, a variety of measurements focusing on deep convection were performed over West Africa. The German research aircraft Falcon based in Ouagadougou (Burkina Faso) investigated the chemical composition in the outflow of large mesoscale convective systems (MCS). Here we analyse two different types of MCS originating north and south of the intertropical convergence zone (ITCZ, ∼10 • N), respectively. In addition to the airborne trace gas measurements, stroke measurements from the Lightning Location Network (LINET), set up in Northern Benin, are analysed. The main focus of the present study is (1) to analyse the trace gas composition (CO, O 3 , NO, NO x , NO y , and HCHO) in the convective outflow as a function of distance from the convective core, (2) to investigate how different trace gas compositions in the boundary layer (BL) and ambient air may influence the O 3 concentration in the convective outflow, and (3) to estimate the rate of lightningproduced nitrogen oxides per flash in selected thunderstorms and compare it to our previous results for the tropics. The MCS outflow was probed at different altitudes (∼10-12 km) and distances from the convective core (<500 km). Trace gas signatures similar to the conditions in the MCS inflow region were observed in the outflow close to the convective core, due to efficient vertical transport. In the fresh MCS outflow, low O 3 mixing ratios in the range of 35-40 nmol mol −1 were Correspondence to: H. Huntrieser (heidi.huntrieser@dlr.de) observed. Further downwind, O 3 mixing ratios in the outflow rapidly increased with distance, due to mixing with the ambient O 3 -rich air. After 2-3 h, O 3 mixing ratios in the range of ∼65 nmol mol −1 were observed in the aged outflow. Within the fresh MCS outflow, mean NO x (=NO + NO 2 ) mixing ratios were in the range of ∼0.3-0.4 nmol mol −1 (peaks ∼1 nmol mol −1 ) and only slightly enhanced compared to the background. Both lightning-produced NO x (LNO x ) and NO x transported upward from the BL contributed about equally to this enhancement. On the basis of Falcon measurements, the mass flux of LNO x in the investigated MCS was estimated to be ∼100 g(N) s −1 . The average stroke rate of the probed thunderstorms was 0.04-0.07 strokes s −1 (here only strokes with peak currents ≥10 kA contributing to LNO x were considered). The LNO x mass flux and the stroke rate were combined to estimate the LNO x production rate. For a better comparison with other published results, LNO x estimates per LINET stroke were scaled to Lightning Imaging Sensor (LIS) flashes. The LNO x production rate per LIS flash was estimated to 1.0 and 2.5 kg(N) for the MCS located south and north of the ITCZ, respectively. If we assume, that these different types of MCS are typical thunderstorms occurring globally (LIS flash rate ∼44 s −1 ), the annual global LNO x production rate was estimated to be ∼1.4 and 3.5 Tg(N) a −1 .

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“…PAN or HNO 3 ). The AFR air mass trajectories ( Figure 5) mostly originate from too far north to pick up substantial biomass burning, soil or lightning emissions of NO x (Richter and Burrows 2002;Yienger and Levy 1995), CO and NMHC (Bechara et al, 2010;Gros et al, 2004;Hao et al, 1996) from the north African savannahs (Figure 19), although an influence from these sources cannot be ruled out. The west African coastal cities of Dakar and Nouakchott as well as higher ship emissions from the north-east to easterly sectors, are also likely to influence NO y and NO x levels observed at Cape Verde.…”

Section: Greenhouse Gasesmentioning

confidence: 99%

Seasonal characteristics of tropical marine boundary layer air measured at the Cape Verde Atmospheric Observatory

et al. 2010

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Observations of the tropical atmosphere are fundamental to the understanding of global changes in air quality, atmospheric oxidation capacity and climate, yet the tropics are under-populated with long-term measurements. The first three years (October 2006 -September 2009) of meteorological, trace gas and particulate data from the global WMO/Global Atmospheric Watch (GAW) Cape Verde Atmospheric Observatory Humberto Duarte Fonseca (CVAO; 16° 51' N, 24° 52' W) are presented, along with a characterisation of the origin and pathways of air masses arriving at the station using the NAME dispersion model and simulations of dust deposition using the COSMO-MUSCAT dust model. The observations show a strong influence from Saharan dust in winter with a maximum in super-micron aerosol and particulate iron and aluminium. The dust model results match the magnitude and daily variations of dust events, but in the region of the CVAO underestimate the measured aerosol optical thickness (AOT) because of contributions from other aerosol. The NAME model also captured the dust events, giving confidence in its ability to correctly identify air mass origins and pathways in this region. Dissolution experiments on collected dust samples showed a strong correlation between soluble Fe and Al and measured solubilities were lower at high atmospheric dust concentrations.Fine mode aerosol at the CVAO contains a significant fraction of non-sea salt components including dicarboxylic acids, methanesulfonic acid and aliphatic amines, all believed to be of oceanic origin. A marine influence is also apparent in the year-round presence of iodine and bromine monoxide (IO and BrO), with IO suggested to be confined mainly to the surface few hundred metres but BrO well mixed in the boundary layer. Enhanced CO 2 and CH 4 and depleted oxygen concentrations are markers for air-sea exchange over the nearby northwest African coastal upwelling area. Long-range transport results in generally higher levels of O 3 and anthropogenic non-methane hydrocarbons (NMHC) in air originating from North America. Ozone/CO ratios were highest (up to 0.42) in European air masses that contain relatively less well-aged air. In air heavily influenced by Saharan dust the O 3 /CO ratio was as low as 0.13, possibly indicating O 3 uptake to dust. Nitrogen oxides (NO x and NO y ) show generally higher concentrations in winter when air mass origins are predominantly from Africa. High photochemical activity at the site is shown by maximum spring/summer concentrations of OH and HO 2 of 9 × 10 6 molecule cm -3 and 6 × 10 8 molecule cm -3 , respectively. After the primary photolysis source, the chemistry of IO and BrO, the abundance of HCHO, and aerosol uptake are important for the HO x budget in this region.3

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Evidence of the impact of deep convection on reactive Volatile Organic Compounds in the upper tropical troposphere during the AMMA experiment in West Africa

Cited by 25 publications

References 46 publications

Emission sources contributing to tropospheric ozone over Equatorial Africa during the summer monsoon

Emission sources contributing to tropospheric ozone over Equatorial Africa during the summer monsoon

Mesoscale convective systems observed during AMMA and their impact on the NO<sub>x</sub> and O<sub>3</sub> budget over West Africa

Seasonal characteristics of tropical marine boundary layer air measured at the Cape Verde Atmospheric Observatory

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Evidence of the impact of deep convection on reactive Volatile Organic Compounds in the upper tropical troposphere during the AMMA experiment in West Africa

Cited by 25 publications

References 46 publications

Emission sources contributing to tropospheric ozone over Equatorial Africa during the summer monsoon

Emission sources contributing to tropospheric ozone over Equatorial Africa during the summer monsoon

Mesoscale convective systems observed during AMMA and their impact on the NO&lt;sub&gt;x&lt;/sub&gt; and O&lt;sub&gt;3&lt;/sub&gt; budget over West Africa

Seasonal characteristics of tropical marine boundary layer air measured at the Cape Verde Atmospheric Observatory

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Mesoscale convective systems observed during AMMA and their impact on the NO<sub>x</sub> and O<sub>3</sub> budget over West Africa