Characterising indoor and ambient particulate matter in Kwazamokuhle, Mpumalanga

Abstract

KwaZamokuhle is typical of the townships home to a large portion of South Africans. If the air quality here can be understood, it may help researchers find better solutions to poor air quality including particulate matter (PM), one of South Africa’s biggest environmental issues. This study focused on the characterisation of indoor/outdoor (I/O) PM4 concentrations at two Reconstruction and Development Program (RDP) houses, one which practiced solid fuel burning and the second solely reliant on electricity. The study further established the I/O relationship of PM4 in the representative dwellings in the community and lastly identified sources of PM4. KwaZamokuhle often has little wind, resulting in smoke from coal stoves remaining trapped by the inversion layer overlying the community, especially during winter. Therefore, although ambient air quality standards are exceeded most days of the year, the exceedances are greatest during the coldest part of winter (June–August). The health risk to the local community from poor air quality from household coal and wood use is thus greatest during the winter. The morning and evening pollution concentration peaks are associated with domestic cooking and space-heating with solid fuels. Respirable particulate matter (PM4) was found to be especially high indoors and could be attributed to the morning and evening peak pollution concentrations. The 24-hr National Ambient Air Quality Standard (NAAQS) for PM2.5 (40 μg m-3) showed exceedances of up to 30% in the morning and 60 % in the evening. The 24-hr PM10 limit (75 μg m-3) was exceeded by a factor of 10. It was found that during periods of the day where no indoor solid fuel burning was practiced, there is still a noticeable increase in PM4 levels inside the dwellings of both fuel-burning and electricity-based households. This finding suggests the infiltration of PM into the dwellings. Source apportionment results showed that during winter, the dominant sources in the coarse fractions were residential coal burning (38 %) and soil dust (28 %). Suspended ambient dust made up the largest contribution to the PM loading when accounting for all sources associated with crustal material in the coarse fraction (42.5 %). During the summer, road and wind-blown dust (43 %), motor vehicle emissions (26 %) and coal combustion (15 %) contributed most to the detected aerosol loading. Domestic coal combustion particulates accounted for 52 % of the fine fraction during the winter in KwaZamokuhle. Emissions from petrol motor vehicles (~11 %) and secondary aerosols (7 %) (sulfate and nitrate) and re-suspended and wind-blown dust (8 %) were also important sources of PM in the township. During the summer motor vehicle emissions (34 %) had the highest contribution to the fine fraction. Road and wind-blown dust (16 %) and secondary aerosols (13 %) contributed almost equal amounts. A large contribution for an as yet unaccounted-for source or sources was present in the fine fraction of the collected PM mass (21 %).