## 3 Results and Discussion
### eBC Mass Concentrations
The Conditional Probability Function (CPF) is a commonly used approach when identifying atmospheric pollutant sources, since it provides directional information concerning major sources (i.e., it shows which wind direction and wind speed intervals are dominated by high concentrations and give the probability of this occurring) [43,44]. Figure 4 shows a CPF plot for eBC over the entire sampling period. It is clear that the highest concentrations (95 th percentile eBC concentration: 2.5 \(\upmu\)g m\({}^{-3}\)) are dominated by south and easterly wind directions. In this case, these directions correspond respectively to (i) a group of single family homes and (ii) one of the most transited roads near to the sampling site. There are very low conditional probabilities of these concentrations being experienced for other wind directions. That is to say, apportions coming from the closest large population city (A Coruna) or coming from the industrial area above-commented are not relevant, as well as the ones coming from the sea (NW winds). Very similar results are observed when representing the CPF plot over the sampling data segmented by the seasons of the year. Figure 4: A CPF (conditional probability function) plot of eBC concentrations > 95 th percentile (2.5 \(\upmu\)g m\({}^{-3}\)) using the entire sampling period. Figure 3: Percentile rose plot of eBC concentrations (\(\upmu\)g m\({}^{-3}\)). With the AE33 aethalometer, ultra-violet light absorption can be assessed. Thus, the independent effect of background wood smoke particles can be identified where wood burning is a major source of personal exposure to carbonaceous particles [45]. [PERSON] et al. [46] commented that organic components of wood smoke particles absorb light at 370 nm more effectively than 880 nm. As commented above, this enhanced absorption (\(\Delta\)C = BC (370 nm)--BC (880 nm)) can serve as an indicator of residential wood smoke particles. In this paper, the enhanced absorption was calculated for absorption at 470 and 950 nm, respectively. As can be seen in Figure 5a,b, the \(\Delta\)C median values were substantially higher during cold seasons compared to warmer seasons, as was also reported by [PERSON] et al. [46] (these authors found a difference between winter and summer of \(\Delta\)C = 0.18 \(\upmu\)g m\({}^{-3}\) (0.24-0.06 \(\upmu\)g m\({}^{-3}\))). During summer, a high dispersion of concentrations was found, probably due to episodes of biomass burning. The diurnal pattern showed an evening peak probably due to the use of biomass for domestic heating in the single family homes near to the sampling site. Figure 5: (**a**) Day of the week variation of median enhanced absorption (\(\Delta\)C) concentrations. (**b**) Hour of day variation of median \(\Delta\)C concentrations. The shading shows the extent to the 25/75 th and 5/95 th quantiles. With regard to Nt concentrations, they are higher on average in the autumn and winter and when the wind comes from the south and east (Figure 7). But in summer during daylight hours Nt increases with different wind directions (east, northeast and southwest). Additionally, but in less proportion, Nt increases in spring, both during daylight hours and night hours, when wind comes from the northwest (from A Coru\(\alpha\) city and its industrial area). Figure 6: **(a)** Day of the week variation of eBC (\(\mu\)g m\({}^{-3}\)) and total number of particles (Nt) (particles cm\({}^{-3}\)) normalized concentrations (variable (s) are divided by their mean values; this helps to compare the shape of the trends for these two variables with different scales). **(b)** Hour of day variation of eBC (\(\mu\)g m\({}^{-3}\)) and Nt (particles cm\({}^{-3}\)) normalized concentrations. The shaded area represents the range of values in which 95% of sample means lie.