Finally, in order to estimate the origin of CAPs on a day-to-day basis, we used some indexes calculating the spatial variability without averaging the data. Only the data containing concentration above the guideline of the Korean government (Table S1) were considered Indeed, the concentration below these limits are not a major issue . If a source is remote, different districts of Ulsan located a few km from each other should be impacted the same way . Therefore, the spatial variabilitybetween different sites should be very low . If a source is local and non-point, like house emission, and the spatial inter-site variability should also be quite low At the opposite, point source such as chemical industries or power plant will impact different areas in different way, and they will lead to high spatial variability between sites.