scholarly journals Optical properties of atmospheric aerosol over Cape Town, Western Cape of South Africa: Role of biomass burning

Atmósfera ◽  
2020 ◽  
Author(s):  
Abdulaziz Tunde Yakubu ◽  
Naven Chetty
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Atmospheric Aerosol ◽  
Cape Town ◽  
Optical Characteristics ◽  
Western Cape ◽  
Climate Trend ◽  
General Terms ◽  
Coarse Mode ◽  
The Impact

The optical characteristics of atmospheric aerosol are vital in the determination of the regional climate trend. Biomass burning is typically known to influence aerosol optical characteristics. Following the incessant biomass burning and the recent drop in precipitation over Western Cape, the aerosol optical properties with a focus on the impact of biomass burning are studied over Cape Town using data from AERONET (Aerosol Robotic Network) and MODIS (Moderate Resolution Imaging Spectroradiometer). In general terms, measurements from both platforms significantly agree on the estimates of aerosol optical depth (AOD) and water vapor content (WVC). The mean AOD 0.075 (± 0.022) and Ångström exponent (AE) 0.63 (± 0.19) derived from AERONET demonstrate the dominance of coarse mode aerosol typical of maritime aerosol. Similarly, aerosol particle size distributions display the predominance of coarse mode particles. However, the derived refractive index is more representative of urban-industrial aerosol. Also, estimated back-trajectories show that more than 70% of the aerosol particles over the region originate over the ocean. Atmospheric vapor increases from winter to summer and mainly influenced by air temperature, supersaturation level, and absorbing aerosol. Furthermore, two significant sources accounted for biomass burning related to high AOD values: local biomass burning and regionally transported aged smoke majorly from elsewhere in Sothern Africa.

scholarly journals Modelling the optical properties of fresh biomass burning aerosol produced in a smoke chamber: results from the EFEU campaign

2007 ◽  
Vol 7 (4) ◽  
pp. 12657-12686 ◽  
Author(s):  
K. Hungershöfer ◽  
K. Zeromskiene ◽  
Y. Iinuma ◽  
G. Helas ◽  
J. Trentmann ◽  
...  
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Absorption Efficiency ◽  
Max Planck ◽  
Fresh Biomass ◽  
Biomass Burning Aerosol ◽  
Smoke Chamber ◽  
The Impact ◽  
Mass Absorption Efficiency

Abstract. A better characterisation of the optical properties of biomass burning aerosol as a function of the burning conditions is required in order to quantify their effects on climate and atmospheric chemistry. Controlled laboratory combustion experiments with different fuel types were carried out at the combustion facility of the Max Planck Institute for Chemistry (Mainz, Germany) as part of the 'Impact of Vegetation Fires on the Composition and Circulation of the Atmosphere' (EFEU) project. Using the measured size distributions as well as mass scattering and absorption efficiencies, Mie calculations provided mean effective refractive indices of 1.60−0.010i and 1.56−0.010i (λ=0.55 μm) for smoke particles emitted from the combustion of savanna grass and an African hardwood (musasa), respectively. The relatively low imaginary parts suggest that the light-absorbing carbon of the investigated fresh biomass burning aerosol is only partly graphitized, resulting in strongly scattering and less absorbing particles. While the observed variability in mass scattering efficiencies was consistent with changes in particle size, the changes in the mass absorption efficiency can only be explained, if the chemical composition of the particles varies with combustion conditions.

scholarly journals Biomass burning and urban emission impacts in the Andes Cordillera region based on in situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)

2019 ◽  
Vol 19 (23) ◽  
pp. 14805-14824
Author(s):  
Aurélien Chauvigné ◽  
Diego Aliaga ◽  
Karine Sellegri ◽  
Nadège Montoux ◽  
Radovan Krejci ◽  
...  
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Light Absorption ◽  
Amazon Basin ◽  
Dry Season ◽  
La Paz ◽  
Extinction Coefficients ◽  
Aerosol Emission ◽  
El Alto ◽  
The Impact

Abstract. This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240 m a.s.l.), in Bolivia. Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz–El Alto, located approximately 20 km away and 1.5 km below the sampling site. The extended multi-year record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96 Mm−1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68 Mm−1 respectively) and higher values during the dry season (0.80, 11.23, and 14.51 Mm−1 respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz–El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28 % to 80 % increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere.

scholarly journals Modelling the optical properties of fresh biomass burning aerosol produced in a smoke chamber: results from the EFEU campaign

2008 ◽  
Vol 8 (13) ◽  
pp. 3427-3439 ◽  
Author(s):  
K. Hungershoefer ◽  
K. Zeromskiene ◽  
Y. Iinuma ◽  
G. Helas ◽  
J. Trentmann ◽  
...  
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Elemental Carbon ◽  
Max Planck ◽  
History Of ◽  
Thermographic Analysis ◽  
Biomass Burning Aerosol ◽  
Smoke Chamber ◽  
The Impact

Abstract. A better characterisation of the optical properties of biomass burning aerosol as a function of the burning conditions is required in order to quantify their effects on climate and atmospheric chemistry. Controlled laboratory combustion experiments with different fuel types were carried out at the combustion facility of the Max Planck Institute for Chemistry (Mainz, Germany) as part of the "Impact of Vegetation Fires on the Composition and Circulation of the Atmosphere" (EFEU) project. The combustion conditions were monitored with concomitant CO2 and CO measurements. The mass scattering efficiencies of 8.9±0.2 m2 g−1 and 9.3±0.3 m2 g−1 obtained for aerosol particles from the combustion of savanna grass and an African hardwood (musasa), respectively, are larger than typically reported mainly due to differences in particle size distribution. The photoacoustically measured mass absorption efficiencies of 0.51±0.02 m2 g−1 and 0.50±0.02 m2 g−1 were at the lower end of the literature values. Using the measured size distributions as well as the mass scattering and absorption efficiencies, Mie calculations provided effective refractive indices of 1.60−0.010i (savanna grass) and 1.56−0.010i (musasa) (λ=0.55 μm). The apparent discrepancy between the low imaginary part of the refractive index and the high apparent elemental carbon (ECa) fractions (8 to 15%) obtained from the thermographic analysis of impactor samples can be explained by a positive bias in the elemental carbon data due to the presence of high molecular weight organic substances. Potential artefacts in optical properties due to instrument bias, non-natural burning conditions and unrealistic dilution history of the laboratory smoke cannot be ruled out and are also discussed in this study.

scholarly journals Space-based retrieval of NO<sub>2</sub> over biomass burning regions: quantifying and reducing uncertainties

2014 ◽  
Vol 7 (10) ◽  
pp. 3431-3444 ◽  
Author(s):  
N. Bousserez
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Shape Factor ◽  
Transport Model ◽  
Sensitivity Analyses ◽  
The Arctic ◽  
Ozone Monitoring Instrument ◽  
Aerosol Optical Properties ◽  
Atmospheric Scattering ◽  
The Impact

Abstract. The accuracy of space-based nitrogen dioxide (NO2) retrievals from solar backscatter radiances critically depends on a priori knowledge of the vertical profiles of NO2 and aerosol optical properties. This information is used to calculate an air mass factor (AMF), which accounts for atmospheric scattering and is used to convert the measured line-of-sight "slant" columns into vertical columns. In this study we investigate the impact of biomass burning emissions on the AMF in order to quantify NO2 retrieval errors in the Ozone Monitoring Instrument (OMI) products over these sources. Sensitivity analyses are conducted using the Linearized Discrete Ordinate Radiative Transfer (LIDORT) model. The NO2 and aerosol profiles are obtained from a 3-D chemistry-transport model (GEOS-Chem), which uses the Fire Locating and Monitoring of Burning Emissions (FLAMBE) daily biomass burning emission inventory. Aircraft in situ data collected during two field campaigns, the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and the Dust and Biomass-burning Experiment (DABEX), are used to evaluate the modeled aerosol optical properties and NO2 profiles over Canadian boreal fires and West African savanna fires, respectively. Over both domains, the effect of biomass burning emissions on the AMF through the modified NO2 shape factor can be as high as −60%. A sensitivity analysis also revealed that the effect of aerosol and shape factor perturbations on the AMF is very sensitive to surface reflectance and clouds. As an illustration, the aerosol correction can range from −20 to +100% for different surface reflectances, while the shape factor correction varies from −70 to −20%. Although previous studies have shown that in clear-sky conditions the effect of aerosols on the AMF was in part implicitly accounted for by the modified cloud parameters, here it is suggested that when clouds are present above a surface layer of scattering aerosols, an explicit aerosol correction would be beneficial to the NO2 retrieval. Finally, a new method that uses slant column information to correct for shape-factor-related AMF error over NOx emission sources is proposed, with possible application to near-real-time OMI retrievals.

scholarly journals AN ASSESSMENT OF SEVERITY OF ENVIRONMENTAL AEROSOL PARTICLES DURING PRECIPITATION

2015 ◽  
Vol 4 (3) ◽  
pp. 81-95
Author(s):  
T. S. Verma ◽  
K. S. Madhava Rao ◽  
Shibu K. John
Keyword(s):  
Mathematical Model ◽  
Biomass Burning ◽  
Atmospheric Aerosols ◽  
Atmospheric Aerosol ◽  
Aerosol Particles ◽  
Carbon Dioxide Concentration ◽  
Objective Criterion ◽  
Different Seasons ◽  
Index Of Severity ◽  
The Impact

Africa is one of the sources of biomass burning emissions. It is estimated that about 6 million tons of fuel per day is consumed in the southern hemisphere. Biomass burning has an important contribution on aerosol particle concentrations in the atmosphere. Efforts have been made to conduct research in Gaborone to monitor the concentration of atmospheric aerosols in atmosphere. These studies were mainly confined to measurement of concentration of aerosols and establishing a relation with determinants such as carbon dioxide concentration, biomass burning, and precipitation among others. However, very little seems to have been done in relating the empirical data to a mathematical model or to study quantitatively the impact of precipitation on the concentration of aerosols larger than 0.3?m in the atmosphere. In this paper we provide an objective criterion for classifying measurements on concentration of atmospheric aerosol particles and build a mathematical model that helps us to understand variations in weekly aerosol concentrations in terms of their severity. We also construct an index of severity which when applied to different seasons under the study period indicates that precipitation significantly scavenges atmospheric aerosols.International Journal of Environment Volume-4, Issue-3, June-August 2015Page: 81-95

scholarly journals Space-based retrieval of NO<sub>2</sub> over biomass burning regions: quantifying and reducing uncertainties

2013 ◽  
Vol 6 (4) ◽  
pp. 6645-6684 ◽  
Author(s):  
N. Bousserez
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Shape Factor ◽  
Sensitivity Analyses ◽  
Aerosol Layer ◽  
Aerosol Optical Properties ◽  
Atmospheric Scattering ◽  
Savanna Fires ◽  
Retrieval Errors ◽  
The Impact

Abstract. The quality of space-based nitrogen dioxide (NO2) retrievals from solar backscatter depends on a priori knowledge of the vertical profiles of NO2 and aerosol optical properties. This information is contained in an air mass factor (AMF), which accounts for atmospheric scattering and is used to convert the measured line-of-sight "slant" columns into vertical columns. In this study we investigate the impact of biomass burning emissions on the AMF in order to quantify NO2 retrieval errors in the Ozone Monitoring Instrument (OMI) products over these sources. Sensitivity analyses are conducted using the Linearized Discrete Ordinate Radiative Transfer (LIDORT) model and the GEOS-Chem chemistry-transport model with an improved daily biomass burning emission inventory. Aircraft in situ data collected during two field campaigns, Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and Dust and Biomass-burning Experiment (DABEX), are used to evaluate the modeled aerosol optical properties and NO2 profiles over Canadian boreal fires and western Africa savanna fires respectively. Biomass burning aerosols increase the AMF by 3 to 15% over boreal fires, while they decrease the AMF by −10 to −30% over savanna fires. The presence of an elevated aerosol layer over west Africa due to the Harmattan front explains the negative aerosol effect over this area. The impact of fires on the AMF is driven by the NO2 shape profile perturbations, which decrease the AMF by −10 to −60% over both regions. Aerosol and shape factor effects are most sensitive to surface reflectance and clouds. In particular, retrieval errors associated with shape factor uncertainties can increase by a factor of 2 due to the presence of clouds. In contrast with conclusions from previous studies, we demonstrate that in the presence of pre-existing clouds, the effect of aerosols on the AMF cannot be fully accounted for through the modified retrieved cloud parameters. Finally, a new method that uses slant column information to correct for shape factor error in the retrieval is proposed and tested over west African fires.

scholarly journals The Power and Perils of Participant Observation in Library and Information Science Research: Reflections on Three South African Studies

Mousaion ◽  
2018 ◽  
Vol 35 (3) ◽  
Author(s):  
Genevieve Hart
Keyword(s):  
South African ◽  
Information Science ◽  
Participant Observation ◽  
Cape Town ◽  
School Libraries ◽  
Research Literature ◽  
Library And Information Science ◽  
Western Cape ◽  
Ethical Challenges ◽  
The Impact

This article reports on three participant observation studies conducted in schools and libraries in South Africa, between 1999 and 2015. The study findings have been reported on elsewhere, thus the focus is on the methodologies used, with the common thread being the author’s preoccupation with the information literacy education of South African pupils. The author’s purpose was to provide evidence of the impact of the dire lack of resources and libraries at South African schools. The first study in 1999 explored how teachers at an underresourced primary school in Cape Town, Western Cape, were coping with the demands of the new curriculum. The second study in 2006 examined two public libraries in a rural town in Mpumalanga, with seven local schools, but no school libraries. The third study in 2015 involved the library at a high school in Kayelitsha township outside Cape Town, which is part of a non-governmental organisation (NGO) project to employ school leavers to manage school libraries. Participant observation is rare in the Library and Information Science (LIS) research literature and the author’s aim is to demonstrate its power to dig beneath the surface. The article uncovers the complex relations and tacit beliefs that existed at the three research sites, which are probably at play in other contexts and which have to be taken into account in planning effective programmes in South African schools and libraries. The article also acknowledges the ethical challenges, arguably inherent in participant observation, which relate to the often sensitive relations among participants, and to the researcher’s positioning.

scholarly journals Closing the reporting gap for childhood tuberculosis in South Africa: improving hospital referrals and linkages

2020 ◽  
Vol 10 (1) ◽  
pp. 38-46
Author(s):  
K. du Preez ◽  
H. S. Schaaf ◽  
R. Dunbar ◽  
A. Swartz ◽  
P. Naidoo ◽  
...  
Keyword(s):  
South Africa ◽  
Multivariable Analysis ◽  
Cape Town ◽  
Linkage To Care ◽  
Western Cape ◽  
Intervention Period ◽  
Loss To Follow Up ◽  
Referral Service ◽  
The Impact

Setting: A referral hospital in Cape Town, Western Cape Province, Republic of South Africa.Objective: To measure the impact of a hospital-based referral service (intervention) to reduce initial loss to follow-up among children with tuberculosis (TB) and ensure the completeness of routine TB surveillance data.Design: A dedicated TB referral service was established in the paediatric wards at Tygerberg Hospital, Cape Town, in 2012. Allocated personnel provided TB education and counselling, TB referral support and weekly telephonic follow-up after hospital discharge. All children identified with TB were matched to electronic TB treatment registers (ETR.Net/EDRWeb). Multivariable logistic regression was used to compare reporting of culture-confirmed and drug-susceptible TB cases before (2007–2009) and during (2012) the intervention.Results: Successful referral with linkage to care was confirmed in 267/272 (98%) and successful reporting in 227/272 (84%) children. Children with drug-susceptible, culture-confirmed TB were significantly more likely to be reported during the intervention period than in the pre-intervention period (OR 2.52, 95%CI 1.33–4.77). The intervention effect remained consistent in multivariable analysis (adjusted OR 2.62; 95%CI 1.31–5.25) after adjusting for age, sex, human immunodeficiency virus status and the presence of TB meningitis.Conclusions: A simple hospital-based TB referral service can reduce initial loss to follow-up and improve recording and reporting of childhood TB in settings with decentralised TB services.

scholarly journals A new method to quantify mineral dust and other aerosol species from aircraft platforms using single particle mass spectrometry

2019 ◽  
Author(s):  
Karl D. Froyd ◽  
Daniel M. Murphy ◽  
Charles A. Brock ◽  
Pedro Campuzano-Jost ◽  
Jack E. Dibb ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Biomass Burning ◽  
Single Particle ◽  
Atmospheric Aerosol ◽  
Mineral Dust ◽  
Sea Salt ◽  
Particle Mass ◽  
Coarse Mode ◽  
Sampling Statistics ◽  
Mass Concentrations

Abstract. Single-particle mass spectrometer (SPMS) instruments characterize the composition of individual aerosol particles in real time. Their fundamental ability to differentiate the externally mixed particle types that constitute the atmospheric aerosol population enables a unique perspective into sources and transformation. However, quantitative measurements by SPMS systems are inherently problematic. We introduce a new technique that combines collocated measurements of aerosol composition by SPMS and size-resolved absolute particle concentrations on aircraft platforms. Quantitative number, surface area, volume, and mass concentrations are derived for climate-relevant particle types such as mineral dust, sea salt, and biomass burning smoke. Additionally, relative ion signals are calibrated to derive mass concentrations of internally mixed sulfate and organic material that are distributed across multiple particle types. The NOAA Particle Analysis by Laser Mass Spectrometry (PALMS) instrument measures size-resolved aerosol chemical composition from aircraft. We describe the identification and quantification of nine major atmospheric particle classes, including sulfate/organic/nitrate mixtures, biomass burning, elemental carbon, sea salt, mineral dust, meteoric material, alkali salts, heavy fuel oil combustion, and a remainder class. Classes can be sub-divided as necessary based on chemical heterogeneity, accumulated secondary material during aging, or other atmospheric processing. Concentrations are derived for sizes that encompass the accumulation and coarse size modes. A statistical error analysis indicates that particle class concentrations can be determined within a few minutes for abundances above ~ 10 ng m−3. Rare particle types require longer sampling times. We explore the instrumentation requirements and the limitations of the method for airborne measurements. Reducing the size resolution of the particle data increases time resolution with only a modest increase in uncertainty. The principal limiting factor to fast time response concentration measurements is statistically relevant sampling across the size range of interest, in particular, sizes D  2 μm for coarse mode analysis. We demonstrate the use of a virtual impactor to enhance sampling statistics for the inherently sparse coarse mode. Performance is compared to other airborne and ground-based composition measurements, and examples of atmospheric mineral dust concentrations are given. The wealth of information afforded by composition-resolved size distributions for all major aerosol types represents a new and powerful tool to characterize atmospheric aerosol properties in a quantitative fashion.

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