Special Session on Optical Properties of Atmospheric Aerosol ― Observation, Measurement Techniques and Model Analysis for Improving the Accuracy of Aerosol Light Absorption Determinations in Polluted Sites

Nopasika A. Xulu This email address is being protected from spambots. You need JavaScript enabled to view it.1, Stuart J. Piketh1, Gregor T. Feig This email address is being protected from spambots. You need JavaScript enabled to view it.3,5, Daniel A. Lack4, Rebecca M. Garland1,2

1 Unit for Environmental Sciences and Management, North-West University, Potchefstroom, 2520, South Africa
2 Natural Resources and the Environment, Council for Scientific and Industrial Research, PO Box 395, Pretoria, 0001, South Africa
3 South African Air Quality Information (SAAQIS), South African Weather Service, Pretoria, South Africa
4 Daniel A Lack, Transport Emissions, Air Quality and Climate, Brisbane, Queensland, Australia
5 Department of Geography, Geoinformatics and Meteorology, University of Pretoria, South Africa


 

Received: September 9, 2019
Revised: May 25, 2020
Accepted: June 8, 2020

 Copyright The Author's institutions. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited. 


Download Citation: ||https://doi.org/10.4209/aaqr.2019.09.0443 

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Cite this article:

Xulu, N.A., Piketh, S.J., Feig, G.T., Lack, D.A. and Garland, R.M. (2020). Characterizing Light‑absorbing Aerosols in a Low‑income Settlement in South Africa. Aerosol Air Qual. Res. https://doi.org/10.4209/aaqr.2019.09.0443


HIGHLIGHTS

  • Absorbing aerosol levels increased in winter and during peak hours in a low-income area
  • Black carbon and brown carbon were estimated from solid fuel burning air pollution
  • Measured absorbing aerosol mass proportions were higher than in Kenya and India.
 

ABSTRACT


Light‑absorbing aerosols, particularly black carbon (BC), have significant impacts on human health and the climate. They are also the least‑studied fraction of atmospheric particles, particularly in residential areas of southern Africa. The optical characteristics of ground‑based light‑absorbing aerosols from Kwadela Township in South Africa are investigated in this study. Daily averaged ambient PM2.5 highest levels were 51.39 µg m‑3 and 32.18 µg m‑3, whereas hourly averages peaked at 61.31 µg m‑3 and 34.69 µg m‑3 during winter and summer, respectively. Levels of daily averaged light–absorbing aerosols were 2.9 times higher (1.89 ± 0.5 μg m‑3) in winter 2014 than in summer 2015 (0.66 ± 0.2 μg m‑3). In both seasons, hourly averaged levels showed bimodal diurnal cycles, which correlated with the PM2.5 diurnal patterns that indicated distinct peaks in the morning and evening. These diurnal cycle peak periods corresponded with the times of increased solid domestic fuel usage, road traffic, and also shallower boundary layer. On average, light‑absorbing aerosols contributed a larger proportion of total ambient PM2.5 levels in winter (6.5 ± 1.0 %) than in summer (3.4 ± 1.0 %). The winter average Absorption Ångstrӧm exponent AAE(370/880 nm) (1.7± 0.5), indicated the dominance of brown carbon (BrC) from biofuel/biomass burning and/or low‑quality coal combustion emissions. In summer, the average AAE(370/950 nm) (1.3 ± 0.7), suggested the presence of BC and BrC in the mornings and evenings possibly from fossil fuel combustion sources. At midday and at night in summer, the AAE was close to 1, suggesting more BC contributions from sources such as diesel emissions during this time. A combination of BC and BrC particulates dominated on 50 % and 5 % of the summer days, respectively, whereas fresh BC were only measured in summer days (23 %). Residential solid‑fuel and/biomass combustion are important sources of light‑absorbing aerosols in this study region, with concomitant human health and environmental impacts.


Keywords: Light absorbing aerosols; Absorption Ångstrӧm exponent; Residential solid fuel combustion; Aethalometer; Mpumalanga; South Africa.



Aerosol Air Qual. Res. 20:-. https://doi.org/10.4209/aaqr.2019.09.0443 


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