Chemical and aerosol characterisation of the troposphere over West Africa during the monsoon period as part of AMMA

Atmospheric Chemistry and Physics (Impact Factor: 5.05). 08/2010; 10(16). DOI: 10.5194/acpd-10-7115-2010
Source: DOAJ


During June, July and August 2006 five aircraft took part in a campaign over West Africa to observe the aerosol content and chemical composition of the troposphere and lower stratosphere as part of the African Monsoon Multidisciplinary Analysis (AMMA) project. These are the first such measurements in this region during the monsoon period. In addition to providing an overview of the tropospheric composition, this paper provides a description of the measurement strategy (flights performed, instrumental payloads, wing-tip to wing-tip comparisons) and points to some of the important findings discussed in more detail in other papers in this special issue.

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Available from: Andreas Minikin
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    • "These factors may have a critical role to play with respect to the 21st century climate change, along with population increases, urbanization, and landmanagement practices. Studies examining the production of tropospheric ozone, another greenhouse gas, remains uncertain in West Africa as multiple sinks and sources (deposition , photolysis, biogenic source of nitrogen, lightning, biomass burning, anthropogenic sources from urban centers, heterogeneous chemical processes) have been modeled and sampled through limited field campaigns [17] [18] [19]. There are still many uncertainties and processes related to ozone chemistry within the annual cycle and over interannual timescales in West Africa that need to be quantified further. "
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    ABSTRACT: We thank many anonymous reviewers for their careful reviews and constructive suggestions in improving each paper.
    Full-text · Article · Jul 2012 · International Journal of Geophysics
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    • "Below 8 km, CO and formaldehyde mixing ratios both decrease with altitude. Above 8 km, CO shows the " C-shaped " profile signature of deep convective transport [Blake et al., 1996; Bechara et al., 2010; Reeves et al., 2010] which uplifts gaseous trace gases from the lower troposphere to the upper troposphere (12 km). "
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    ABSTRACT: 1] In situ measurements of formaldehyde (CH 2 O) onboard four European research aircraft in August 2006 as part of the African Monsoon Multidisciplinary Analysis (AMMA) experiment in West Africa are used (1) to examine the redistribution of CH 2 O by mesoscale convective systems (MCS) in the tropical upper troposphere (UT), (2) to evaluate the scavenging efficiency (SE) of CH 2 O by MCS and (3) to quantify the impact of CH 2 O on UT photooxidant production downwind of MCS. The intercomparison of CH 2 O measurements is first tested, providing a unique and consistent 3-D-spatially resolved CH 2 O database in background and convective conditions. While carbon monoxide (CO) is vertically uplifted by deep convection up to 12 km, CH 2 O is also affected by cloud processing as seen from its ratio relative to CO with altitude. A new observation-based model is established to quantify the SE of CH 2 O. This model shows that convective entrainment of free tropospheric air cannot be neglected since it contributes to 40% of the convective UT air. For the 4 studied MCS, SE shows a large variability within a 4% to 39% range at a relative standard deviation of 30%, which is consistent with MCS features. A time-dependent photochemical box model is applied to convective UT air. After convection, 60% of CH 2 O is due to its photochemical production rather than to its direct transport. Model results indicate that CH 2 O directly injected by convection does not impact ozone and HOx production in the tropical UT of West Africa. NOx and anthropogenic hydrocarbon precursors dominate the secondary production of CH 2 O, ozone and HOx. Citation: Borbon, A., et al. (2012), Transport and chemistry of formaldehyde by mesoscale convective systems in West Africa during AMMA 2006, J. Geophys. Res., 117, D12301, doi:10.1029/2011JD017121.
    Full-text · Article · Jun 2012 · Journal of Geophysical Research Atmospheres
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    • "are quite low (∼20–40 ppb), where the latitudinal variability in the zonal mean has features similar to those observed by airborne observations [29]. For latitudes nearer to the equator and above 20 • N, the mixing ratios increase to >50 ppb due to the influence of BB in southern Africa and influx from Europe, respectively. "
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    ABSTRACT: Particle and trace gas emissions due to anthropogenic activity are expected to increase significantly in West Africa over the next few decades due to rising population and more energy intensive lifestyles. Here we perform 3D global chemistry-transport model calculations for 2025 and 2050 using both a "business-as-usual" (A1B) and "clean economy" (B1) future anthropogenic emission scenario to focus on the changes in the distribution and uncertainties associated with tropospheric O 3 due to the various projected emission scenarios. When compared to the present-day troposphere we find that there are significant increases in tropospheric O 3 for the A1B emission scenario, with the largest increases being located in the lower troposphere near the source regions and into the Sahel around 15–20 • N. In part this increase is due to more efficient NO x re-cycling related to increases in the background methane concentrations. Examining the uncertainty across different emission inventories reveals that there is an associated uncertainty of up to ∼20% in the predicted increases at 2025 and 2050. For the upper troposphere, where increases in O 3 have a more pronounced impact on radiative forcing, the uncertainty is influenced by transport of O 3 rich air from Asia on the Tropical Easterly Jet.
    Full-text · Article · Oct 2011 · International Journal of Geophysics
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