Comparison of source apportionment targeting hot-spot concentration and average population exposure

Source apportionment (SA) is an essential first step in supporting the design of air quality plans. However, SA results can strongly be influenced by the choice of setting parameters, such as the indicator used. In this study, we assess how different choices of indicator for PM_2.5 (hot spot concentrations, average population exposure and average concentration) impact the SA results. Our analysis reveals that, in general, there is a good correlation between results obtained with these three indicators. The correlation is higher for sectors that are well-distributed spatially at city scale, such as residential and traffic, and lower for sectors characterized by important local emissions, such as waste and shipping. In most cases, results based on average indicators (average population exposure and average concentration) underestimates those based on the concentration hot spot location. Interestingly, we find that the choice of indicator has a strong impact on the estimation of the local contribution to air pollution in the city, but the relative share of the sectors is generally preserved across indicators. In other words, the priority sector remains similar, but the resulting scale of action can differ in some cities.