Seasonal characteristics of spectral aerosol optical properties at a sub-Saharan site

Nwofor, O. K.; Chineke, Theo Chidiezie; Pinker, R. T.

doi:10.1016/j.atmosres.2006.11.002

Cited by 14 publications

(16 citation statements)

References 24 publications

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“…Thus biomass burning aerosol which originates at latitudes south of 11°N (Figure 1), may be advected hundreds of kilometers north of its origin. This is the reason why biomass burning aerosol that is detected in the regions of active fires such as the Djougou site [e.g., Mallet et al , 2008; Pelon et al , 2008] and Ilorin site [ Nwofor et al , 2007] is so frequently detected at altitude over Niamey [e.g., Heese and Wiegner , 2008; Johnson et al , 2008b] site.…”

Section: Overview Of Meteorological Conditions Affecting Aerosol Tranmentioning

confidence: 99%

Overview of the Dust and Biomass‐burning Experiment and African Monsoon Multidisciplinary Analysis Special Observing Period‐0

et al. 2008

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[1] The African Monsoon Multidisciplinary Analysis (AMMA) is a major international campaign investigating far-reaching aspects of the African monsoon, climate and the hydrological cycle. A special observing period was established for the dry season (SOP0) with a focus on aerosol and radiation measurements. SOP0 took place during January and February 2006 and involved several ground-based measurement sites across west Africa. These were augmented by aircraft measurements made by the Facility for Airborne Atmospheric Measurements (FAAM) aircraft during the Dust and Biomass-burning Experiment (DABEX), measurements from an ultralight aircraft, and dedicated modeling efforts. We provide an overview of these measurement and modeling studies together with an analysis of the meteorological conditions that determined the aerosol transport and link the results together to provide a balanced synthesis. The biomass burning aerosol was significantly more absorbing than that measured in other areas and, unlike industrial areas, the ratio of excess carbon monoxide to organic carbon was invariant, which may be owing to interaction between the organic carbon and mineral dust aerosol. The mineral dust aerosol in situ filter measurements close to Niamey reveals very little absorption, while other measurements and remote sensing inversions suggest significantly more absorption. The influence of both mineral dust and biomass burning aerosol on the radiation budget is significant throughout the period, implying that meteorological models should include their radiative effects for accurate weather forecasts and climate simulations. Generally, the operational meteorological models that simulate the production and transport of mineral dust show skill at lead times of 5 days or more. Climate models that need to accurately simulate the vertical profiles of both anthropogenic and natural aerosols to accurately represent the direct and indirect effects of aerosols appear to do a reasonable job, although the magnitude of the aerosol scattering is strongly dependent upon the emission data set.

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Section: Overview Of Meteorological Conditions Affecting Aerosol Tranmentioning

confidence: 99%

Overview of the Dust and Biomass‐burning Experiment and African Monsoon Multidisciplinary Analysis Special Observing Period‐0

et al. 2008

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“…Due to position of Nigeria in sub-Sahara West Africa, aerosol pollution is a familiar phenomenon of which its concentrations exhibit strong seasonal variability mainly driven by seasonally changed air mass (northeasterly trade wind and southwesterly trade wind) patterns during Harmattan (November-March) and Summer (April-October) seasons [3]. The two main seasons not only dictate variations in concentrations, but also types, and distributions of aerosols both spatially and temporally.…”

Section: Introductionmentioning

confidence: 99%

Seasonal Variations of Aerosol Optical Properties and Identification of Different Aerosol Types Based on AERONET Data over Sub-Sahara West-Africa

Balarabe

Abdullah

Adlan

2016

ACS

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The uncertainty in the quantification of aerosol properties such as concentration, size, and composition, spatially and temporally makes regional studies important. Therefore, this study presents seasonal variations of aerosol optical properties over Ilorin (8˚32'N, 4˚34'E), Nigeria. Long-term (1998-2013) records of aerosol optical depth (AOD) and angstrom exponent α, from ground-based Aerosol Robotic Network (AERONET) are used to study the seasonal variability, characteristics and types of aerosol. The study showed that seasonal variations (Harmattan and Summer) result in different aerosol concentration, characteristics, and types. The magnitude and sensitivity of AOD to wavelength are found low in Summer with significant increase during Saharan dust transport season (Harmattan). The average mean AODs are 0.73 ± 0.50, 0.97 ± 0.52 and 0.46 ± 0.29 with corresponding mean angstrom of 0.66 ± 0.36, 0.68 ± 0.34, and 0.64 ± 0.37 for the entire period, Harmattan and Summer seasons. High frequency of occurrence of angstrom exponent below 1 (78% and 81%) which were observed during Harmattan and Summer indicates that the particles are generally coarse in mode. The results revealed that for both Harmattan and Summer seasons, the dominant aerosol was dust (DA) with frequency of occurrence of 82% and 79%. However, mixed aerosol (MIXA) (14.4%) is the second dominant case during Harmattan while in Summer maritime aerosol (MA) (9.1%) associated with transport due to southwesterly trade wind is the second dominant aerosol. This conclusion is supported by size distribution data for the study site which showed that large volume of aerosol particle size are enclosed in largely coarse mode range in all seasons. A 7-day back trajectory seasonal frequency plot sourced from the Hysplit Single Particles Lagrangian Integrated Trajectory model (Hysplit_4 model) shows that dust are transported from the Saha-* Corresponding author. ra during north-easterly trade wind flow while the observed marine aerosols are conveyed by the southwesterly trade wind influences to the study site.

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“…Maximum α values are largest in March, at the end of the dry season, correlating closely to the monthly highest AOD, and are lowest in June or July during the wet season. These maximum monthly estimates of α (1.68 -1.52) are at the top when compared to similar studies, such as Pinker et al [57] in southwestern United States (α = 1.60), Masmoudi et al [6] in north Africa (α = 0.88), Nwofor et al [21] in Ilorin, Nigeria (α = 0.70) Ogunjobi et al [25] in five west African sites (α = 1.07-0.93 for urban pollution), Eck et al [58] in southern Africa (α > 1.80 for biomass burning season) and Schafer et al [50] in Amazonia (α > 1.80 for smoke).…”

Section: Discussionmentioning

confidence: 79%

Aerosol Optical Properties at Four Sites in Thailand

Janjai¹,

Núñez²,

Masiri³

et al. 2012

ACS

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This paper presents column integrated aerosol optical properties including aerosol optical depth (AOD), Angstrom wavelength exponent (), single scattering albedo (SSA), and size distribution from ground-based measurements at four sites in Thailand: Chiang Mai (18.78˚N, 98.98˚E), Ubon Ratchathani (15.25˚N, 104.87˚E), Nakhon Pathom (13.82˚N, 100.04˚E), and Songkhla (7.2˚N, 100.60˚E). Results show a marked seasonal trend in AOD at 500 nm for the first three stations, with the monthly average maxima of 0.92, 0.78 and 0.61 for Chiang Mai, Ubon Ratchathani and Nakhon Pathom, respectively. These maxima occur in the dry season (November-April). Minimum values for these stations were recorded during the wet season (May-October). A similar pattern is exhibited in the  for the three stations, with maxima in the dry season and minima in the wet season. The lowest SSA values occur at Chiang Mai, which means this station has the highest absorption, with the highest SSA values occurring at Songkhla which corresponds to the lowest absorption. The southern station at Songkhla differs from the other three as it has less local pollution sources and is subjected to the influence of the tropical maritime environment. AOD at Songkhla maintains a low and more constant value year round with the maximum monthly average AOD of 0.27 and the minimum of 0.16. Diurnal changes in AOD at the four stations are discussed and related to various external variables.

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Seasonal characteristics of spectral aerosol optical properties at a sub-Saharan site

Cited by 14 publications

References 24 publications

Overview of the Dust and Biomass‐burning Experiment and African Monsoon Multidisciplinary Analysis Special Observing Period‐0

Overview of the Dust and Biomass‐burning Experiment and African Monsoon Multidisciplinary Analysis Special Observing Period‐0

Seasonal Variations of Aerosol Optical Properties and Identification of Different Aerosol Types Based on AERONET Data over Sub-Sahara West-Africa

Aerosol Optical Properties at Four Sites in Thailand

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