DN-PMF as a Sensitivity Test for Conventional PMF (C-PMF) Source Apportionment in Three Cities in South Africa, 2017–2018

Source apportionment through factorization is a common method for identifying sources of air pollution. Both PCA and DN-PMF have assumptions, strengths, and limitations. Assigning sources to factors is inherently subjective and can introduce bias. PCA for the number of sources, C-PMF and DN-PMF is performed on data from three cities which were sampled at the same time, 16 April 2017 to 18 April 2018. The DN-PMF was able to give seasonal information to support the source apportionment. Results of the PCA included 6 factors for Thohoyandou and Pretoria and 7 factors for Cape Town. At the two large city sites, the C-PMF presented a dominant coal emissions source (29% and 35.6%) yearly and a strong biomass source during winter (24% and 17%). The dominant yearly source shifted to vehicular emissions with the DN-PMF model in Pretoria and Cape Town (41% and 12%) and coal burning at Thohoyandou (33%). By considering the mixing layer and meteorological conditions the factors shifted while keeping the dominant Cl-Pb and Cu-Zn tracer combinations.