the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics

The influence of biogenic emissions from Africa on tropical tropospheric ozone during 2006: a global modeling stud

Airborne measurements of biomass burning products over Africa

Ozone has been observed in elevated concentrations by satellites over hitherto believed 'background' areas. There is meteorological evidence that these ozone 'plumes' found over the Atlantic ocean originate from biomass fires on the African continent. Therefore we have investigated ozone and assumed precursor compounds over African regions. The measurements revealed large photosmog layers in altitudes between 1.5 and 4 km. Here we will focus on some results of ozone mixing ratios obtained during the DECAFE 91/FOS experiment and estimate the relevance of biomass burning as a source by comparing the strength of this source to stratospheric input

The influence of biogenic emissions from Africa on tropical tropospheric ozone during 2006: a global modeling study

We have performed simulations using a 3-D global chemistry-transport model to investigate the influence that biogenic emissions from the African continent exert on the composition of the troposphere in the tropical region. For this purpose we have applied two recently developed biogenic emission inventories provided for use in large-scale global models (Granier et al., 2005; LathiSre et al., 2006) whose seasonality and temporal distribution for biogenic emissions of isoprene, other volatile organic compounds and NO is markedly different. The use of the 12 year average values for biogenic emissions provided by LathiSre et al. (2006) results in an increase in the amount of nitrogen sequestrated into longer lived reservoir compounds which contributes to the reduction in the tropospheric ozone burden in the tropics. The associated re-partitioning of nitrogen between PAN, HNO3 and organic nitrates also results in a similar to 5% increase in the loss of nitrogen by wet deposition. At a global scale there is a reduction in the oxidizing capacity of the model atmosphere which increases the atmospheric lifetimes of CH4 and CO by similar to 1.5% and similar to 4%, respectively. Comparisons against a range of different measurements indicate that applying the 12 year average of LathiSre et al. (2006) improves the performance of TM4_AMMA for 2006 in the tropics. By the use of sensitivity studies we show that the release of NO from soils in Africa accounts for between similar to 2-45% of tropospheric ozone in the African troposphere, similar to 10% in the upper troposphere and between similar to 5-20% of the tropical tropospheric ozone column over the tropical Atlantic Ocean. The subsequent reduction in OH over the source regions allows enhanced transport of CO out of the region. For biogenic volatile organic C1 to C3 species released from Africa, the effects on tropical tropospheric ozone are rather limited, although this source contributes to the global burden of VOC by between similar to 2-4% and has a large influence on the organic composition of the troposphere over the tropical Atlantic Ocean

Clues for a standardised thermal-optical protocol for the assessment of organic and elemental carbon within ambient air particulate matter

Along with some research networking programmes, the European Directive 2008/50/CE requires chemical speciation of fine aerosol (PM_2.5), including elemental (EC) and organic carbon (OC), at a few rural sites in European countries. Meanwhile, the thermal-optical technique is considered by the European and US networking agencies and normalisation bodies as a reference method to quantify EC–OC collected on filters. Although commonly used for many years, this technique still suffers from a lack of information on the comparability of the different analytical protocols (temperature protocols, type of optical correction) currently applied in the laboratories. To better evaluate the EC–OC data set quality and related uncertainties, the French National Reference Laboratory for Ambient Air Quality Monitoring (LCSQA) organised an EC–OC comparison exercise for French laboratories using different thermal-optical methods (five laboratories only). While there is good agreement on total carbon (TC) measurements among all participants, some differences can be observed on the EC / TC ratio, even among laboratories using the same thermal protocol. These results led to further tests on the influence of the optical correction: results obtained from different European laboratories confirmed that there were higher differences between OC_TOT and OC_TOR measured with NIOSH 5040 in comparison to EUSAAR-2. Also, striking differences between EC_TOT / EC_TOR ratios can be observed when comparing results obtained for rural and urban samples, with EC_TOT being 50% lower than EC_TOR at rural sites whereas it is only 20% lower at urban sites. The PM chemical composition could explain these differences but the way it influences the EC–OC measurement is not clear and needs further investigation. Meanwhile, some additional tests seem to indicate an influence of oven soiling on the EC–OC measurement data quality. This highlights the necessity to follow the laser signal decrease with time and its impact on measurements. Nevertheless, this should be confirmed by further experiments, involving more samples and various instruments, to enable statistical processing. All these results provide insights to determine the quality of EC–OC analytical methods and may contribute to the work toward establishing method standardisation

L'initiative européenne "Suivi global pour l'environnement et la sécurité'' et le protocole de Kyoto

International audienceEn 1992 la Convention Cadre des Nations Unies pour le Contrôle du Changement du Climat (UNFCCC) a montré la prise de conscience internationale des effets néfastes de l'accumulation dans l'atmosphère des gaz à effet de serre, conduisant à un réchauffement climatique, sous l'effet direct ou indirect des activités anthropiques. Le Protocole de Kyoto, adopté en 1997, a fixé des engagements quantitatifs que les parties signataires s'engageaient à respecter. Ceci suppose des moyens d'observation afin de comprendre, modéliser, mesurer l'évolution des sources et des puits de gaz à effet de serre, et tout particulièrement celles sur lesquelles l'Homme peut avoir une influence directe. Conjointement aux mesures in situ, l'observation de la Terre par satellite s'avère un moyen puissant pour répondre à cet objectif. L'Europe, comme le rappelle le "Manifeste de Baveno" adopté par un certain nombre d'agences impliquées dans les activités spatiales, dispose d'atouts majeurs pour remplir de tels objectifs. Le présent article s'efforce de donner une vue synthétique des différentes informations à rassembler pour le suivi des clauses du Protocole de Kyoto, de l'UNFCCC et de leurs conséquences globales sur le changement climatique, mettant en évidence les résultats obtenus, les moyens à entreprendre, les recherches restant à mener, pour atteindre ces buts

Trends and seasonal variability in ammonia across major biomes in western and central Africa inferred from long-term series of ground-based and satellite measurements

Ammonia (NH3) is the most abundant alkaline component in the atmosphere. Changes in NH3 concentrations have important implications for atmospheric chemistry, air quality, and ecosystem integrity. We present a long-term ammonia (NH3) assessment in the western and central African regions within the framework of the International Network to study Deposition and Atmospheric chemistry in Africa (INDAAF) programme. We analyse seasonal variations and trends in NH3 concentrations and total column densities along an African ecosystem transect spanning dry savannas in Banizoumbou, Niger, and Katibougou, Mali; wet savannas in Djougou, Benin, and Lamto, Côte d'Ivoire; and forests in Bomassa, Republic of the Congo, and Zoétélé, Cameroon. We use a 21-year record of observations (1998–2018) from INDAAF passive samplers and an 11-year record of observations (2008–2018) of atmospheric vertical column densities from the Infrared Atmospheric Sounding Interferometer (IASI) to evaluate NH3 ground-based concentrations and total column densities, respectively. Climatic data (air temperature, rainfall amount, and leaf area index), as well as ammonia emission data of biomass combustion from the fourth version of the Global Fire Emissions Database (GFED4) and anthropogenic sources from the Community Emissions Data System (CEDS), were compared with total NH3 concentrations and total columns over the same periods. Annual mean ground-based NH3 concentrations are around 5.7–5.8 ppb in dry savannas, 3.5–4.7 ppb in wet savannas, and 3.4–5.6 ppb in forests. Annual IASI NH3 total column densities are 10.0–10.7 × 1015 molec. cm−2 in dry savanna, 16.0–20.9 × 1015 molec. cm−2 in wet savanna, and 12.4–13.8 × 1015 molec. cm−2 in forest stations. Non-parametric statistical Mann–Kendall trend tests applied to annual data show that ground-based NH3 concentrations increase at Bomassa (+2.56 % yr−1) but decrease at Zoétélé (−2.95 % yr−1) over the 21-year period. The 11-year period of IASI NH3 total column density measurements show yearly increasing trends at Katibougou (+3.46 % yr−1), Djougou (+2.24 % yr−1), and Zoétélé (+3.42 % yr−1). From the outcome of our investigation, we conclude that air temperature, leaf area index, and rainfall combined with biomass burning, agricultural, and residential activities are the key drivers of atmospheric NH3 in the INDAAF stations. The results also show that the drivers of trends are (1) agriculture in the dry savanna of Katibougou; (2) air temperature and agriculture in the wet savanna of Djougou and Lamto; and (3) leaf area index, air temperature, residential, and agriculture in the forest of Bomassa.</p

Conditions of malaria transmission in Dakar from 2007 to 2010

Background: Previous studies in Dakar have highlighted the spatial and temporal heterogeneity of Anopheles gambiae s.l. biting rates. In order to improve the knowledge of the determinants of malaria transmission in this city, the present study reports the results of an extensive entomological survey that was conducted in 45 areas in Dakar from 2007 to 2010. Methods: Water collections were monitored for the presence of anopheline larvae. Adult mosquitoes were sampled by human landing collection. Plasmodium falciparum circumsporozoite (CSP) protein indexes were measured by ELISA (enzyme-linked immunosorbent assay), and the entomological inoculation rates were calculated. Results: The presence of anopheline larvae were recorded in 1,015 out of 2,683 observations made from 325 water collections. A water pH of equal to or above 8.0, a water temperature that was equal to or above 30 degrees C, the absence of larvivorous fishes, the wet season, the presence of surface vegetation, the persistence of water and location in a slightly urbanised area were significantly associated with the presence of anopheline larvae and/or with a higher density of anopheline larvae. Most of the larval habitats were observed in public areas, i.e., freely accessible. A total of 496,310 adult mosquitoes were caught during 3096 person-nights, and 44967 of these specimens were identified as An. gambiae s.l. The mean An. gambiae s.l. human-biting rate ranged from 0.1 to 248.9 bites per person per night during the rainy season. Anopheles arabiensis (93.14%), Anopheles melas (6.83%) and An. gambiae s.s. M form (0.03%) were the three members of the An. gambiae complex. Fifty-two An. arabiensis and two An. melas specimens were CSP-positive, and the annual CSP index was 0.64% in 2007, 0.09% in 2008-2009 and 0.12% in 2009-2010. In the studied areas, the average EIR ranged from 0 to 17.6 infected bites per person during the entire transmission season. Conclusion: The spatial and temporal heterogeneity of An. gambiae s.l. larval density, adult human-biting rate (HBR) and malaria transmission in Dakar has been confirmed, and the environmental factors associated with this heterogeneity have been identified. These results pave the way for the creation of malaria risk maps and for a focused anti-vectorial control strategy