Characterisation of respirable indoor particulate matter in South African low-income settlements

Abstract

Air pollution is a leading health risks that individuals face daily. Emissions and contribution from scheduled industrial sources has been a focus within South Africa air quality management for decades. In recent years, the importance of dense, low-income residential environments has been recognised due to ambient air quality measurements conducted with these communities. Extremely high levels of particulate matter were recorded in part created by residential solid fuel combustion. Indoor air quality studies in South Africa tend to have a narrow geographic focus while investigating small sample groups, mostly on a case-study basis. Existing studies further have not considered the apportionment of indoor sources. These limitations have impeded a comprehensive understanding of the air pollution problem facing our most vulnerable population groups. In this thesis, the respirable (PM4) fraction of indoor particulate matter was examined within two coal-burning- (KwaDela and KwaZamokuhle), one urban- (Jouberton), and two wood-burning- (Agincourt and Giyani) low-income settlements in South Africa. This included: i) a field evaluation of the photometric particulate monitoring used; ii) an assessment of the status of air quality with respect to the PM4 mass concentrations; iii) the identification of possible sources contributing to the indoor environment; and iv) an Characterisation of respirable indoor particulate matter in South African low-income settlements Abstract Page | ii evaluation of the relationship between the observed synoptic circulations, local meteorology and indoor PM4 loadings. PM4 data were collected in the indoor environment of households within the above mentioned settlements, between 2013 and 2017, across 21 individual seasonal sampling campaigns. Three main method of sampling were conducted, namely i) continuous monitoring by photometric instruments (DustTrak, DustTrak II, and SidePak); ii) gravimetric filter sampling which were analysed by WD-XRF for the elemental chemical composition; and iii) a collocated sampling method for the field evaluation of the instrumentations. The photometric instruments both over-and underestimated the continuous indoor PM4 mass concentrations which resulted in the development of twenty-nine (29) PCFs. The comparability of different instrument models improved between 15 and 46% when applying instrument-specific PCFs calculated for the specific micro-environment. A conversion factor of 0.92 was determined to convert indoor PM4- to PM2.5 mass concentration. This enables some comparison of the measurements with ambient air quality standards. The low-income settlement had a mean (±SD) indoor PM4 loading of 116 (±357) μg.m-3. Coal-burning (137 (±403) μg.m-3) communities experiencing PM4 loadings which are three times higher than the urbanised- (53 (±171) μg.m-3) and wood-burning (58 (±143) μg.m-3) communities. A distinct bi-modal diurnal pattern is present within all the communities. The indoor PM2.5 were above the 24-hr NAAQS (40 μg.m-3) and WHO (25 μg.m-3) guideline for~57 and 76% of the daily averages. The qualitative source contribution was estimated based on the elemental mass concentrations, crustal enrichment factors, and principal component analysis (PCA). The main sources included crustal soil-, road traffic-, solid fuel combustion-, waste burning-, and biomass burning emissions. All households (regardless of their fuel use) in dense-, low-income settlements experience high levels of indoor PM4. Current health impact assessments likely grossly underestimate the scale of the problem. This highlights the need to improve understanding at a local scale and formulate mitigation strategies for all low-income communities individually.