Measurement report: Size-resolved chemical characterisation of aerosols in low-income urban settlements in South Africa
Authors: Segakweng Constance K. , van Zyl Pieter G. , Liousse Cathy , Beukes Johan P. , Swartz Jan-Stefan , Gardrat Eric , Dias-Alves Maria , Language Brigitte , Burger Roelof P. , Piketh Stuart J. 
Published: August 2022

Abstract. Naturally and anthropogenically emitted aerosols, which are determined by
their physical and chemical properties, have an impact on both air quality
and the radiative properties of the earth. An important source of
atmospheric particulate matter (PM) in South Africa is household combustion
for space heating and cooking, which predominantly occurs in low-income
urban settlements. The aim of this study was to conduct a detailed
size-resolved assessment of chemical characteristics of aerosols associated
with household combustion through the collection of particulates in
low-income urban settlements in South Africa to quantify the extent
of the impacts of atmospheric pollution. Outdoor (ambient) and indoor
aerosols in different size fractions were collected during summer and winter
in four low-income urban settlements located in the north-eastern interior
on the South African Highveld, i.e. Kwadela, Kwazamokuhle, Zamdela, and
Jouberton. Mass concentration and chemical composition was determined
for three size fractions, namely, PM1, PM2.5, and PM2.5−10.
The highest concentrations of particulates were measured indoors with the
highest mass concentration determined in the indoor PM2.5−10 (coarse)
size fraction. However, the highest mass concentrations were determined in
PM1 in all outdoor aerosol samples collected during winter and summer,
and in indoor samples collected during summer. Significantly higher concentrations were determined for SO4-2 in
outdoor and indoor particulates compared to other ionic species, with
NH4+ and NO3- being the second most abundant.
SO4-2 and NH4+ almost exclusively occurred in the
PM1 size fraction, while NO3- was the major constituent in
the larger size fractions. The highest SO4-2 levels were recorded
for the winter and summer outdoor campaigns conducted at Zamdela, while
NO3- and NH4+ concentrations were higher during the
winter outdoor campaign. The combined concentrations of trace elements were
higher for indoor particulates compared to outdoor aerosols, while the total
trace element concentrations in PM1 were substantially higher than
levels thereof in the two larger size fractions of particulates collected
during all sampling campaigns. No distinct seasonal trend was observed for the concentrations of trace
elements. Na, Ca, and Cr had the highest concentrations in particulates
collected during outdoor and indoor sampling campaigns. Ni concentrations in
outdoor and indoor aerosols exceeded the annual average European standard.
PM1 collected during all sampling campaigns in low-income urban
settlements had the highest organic carbon (OC) and elemental carbon (EC)
concentrations. The highest OC and EC levels were determined in PM1 collected during the winter indoor campaign. OC and EC concentrations were
highest during winter, which can be attributed to changes in meteorological
patterns and increased household combustion during winter. Low OC/EC ratios
determined for particulates collected in low-income urban settlements are
indicative of OC and EC being mainly associated with local sources of these
species. OC concentrations determined in this study were an order of
magnitude lower than OC concentrations determined for ambient aerosols
collected in the north-eastern interior of South Africa, while similar EC
levels were measured. According to estimated dust concentrations, it was
indicated that dust is the major constituent in all size ranges of
particulates collected in this study, while trace elements were the second
most abundant. However, trace elements made the highest contribution to
indoor PM1 and PM1−2.5 mass. Mass concentrations and chemical
concentrations determined for aerosols collected in low-income settlements
reflect the regional impacts of anthropogenic sources in the north-eastern
interior of South Africa and the influence of local sources.