## 3 Results and Discussion
### Source Apportionment of eBC
Moreover, Figure 9b shows wider shades during the early morning hours and the late evening of summer, probably due to (i) episodes of thermal inversion, which retain pollutants during these hours, and (ii) traditional summer barbecues around the beach and in the single family homes starting at 5 a.m. (UTC). This increase in some summertime sources of biomass burning was previously observed in London by [PERSON] et al. (2018). Figure 9: (**a**) Day of the week variation of eBCbb and eBCff (\(\mathrm{\SIUnitSymbolMicro g}\) m\({}^{-3}\)) concentrations. (**b**) Hour of day variation of eBCbb and eBCff (\(\mathrm{\SIUnitSymbolMicro g}\) m\({}^{-3}\)) concentrations. Shaded area represents the range of values in which 95% of sample means lie. In the following Figures 10 and 11, the data are split by day and night-time and the season of the year, and here the trends can be observed. In the case of eBCff, south-east and north-west wind directions contribute most to mean concentrations in autumn and spring, both during the day and at night. This could be explained by the prevailing wind direction in autumn and winter from SW, where there is a road and also an industrial area (see Figure 1). In the same seasons, NW is the dominant wind direction, which could bring pollutants from the city of A Coruna and its industrial area. No land-sea breeze effect was observed. With regard to eBCbb concentrations, south wind directions, where several single family homes are located, contribute most to overall concentrations in autumn and winter during night-time: wood stoves for domestic heating. Besides, episodes of open-air biomass burning and barbecues probably contribute to the high percentile found in summer during daylight hours. No land-sea breeze effect was observed. Figure 11: Percentile rose plot of eBCbb concentrations (\(\mu\)g m\({}^{-3}\)). Figure 10: Percentile rose plot of eBCff concentrations (\(\mu\)g m\({}^{-3}\)). Once the previous analysis had been carried out with the entire sampling data, the daily values of both eBC and Nt were represented (not shown here) and the days in which the highest values of the two pollutants occurred were chosen. Once this selection of days was made, they were compared with the \"classification of days with Saharan dust intrusion and with intrusion of particulate matter from biomass combustion provided by the Ministry for Ecological Transition\" ([[https://www.miteco.gob.es/](https://www.miteco.gob.es/)]([https://www.miteco.gob.es/](https://www.miteco.gob.es/))), to see if they coincided with any of those long-distance transport events. Two events were detected, and they are commented next through Figures 12 and 13. The data related to both events were not excluded in the overall analysis since it was confirmed that they do not affect the analysis. As shown in Figure 12, we found a strong episode with high levels of the two pollutants during 4 February 2016, which coincides with an intense fresh biomass burning episode. Another episode with high concentrations of eBC and Nt was detected from 26 October to 4 November 2016. In this case, dust and extremely fresh biomass burning episodes during those days were identified. This was confirmed by the high hourly levels found for eBCff and eBCbb (marked in yellow in Figure 13) during this period. With regard to Nt, and as happened with the above-mentioned episode, almost every hourly value are below 20,000 particles cm\({}^{-3}\) during this episode. Figure 12: eBC and Nt concentrations during an episode of biomass combustion during 4 February 2016. Figure 13: eBCff and eBCbb concentrations during a strong episode of Saharan dust intrusion and biomass combustion from 26 October to 4 November 2016.