## 3 Results and Discussion
### Application of the Modified Methodology
Now the amount of days still exceeding the limit value is very well comparable as if DD days were identified using model and trajectory analysis. An influence on the exceedance of the 35 day/year limit remains scarce (compare column 3 and 5 in Table 4) and occurs only in one year (2015) when the adapted methodology using the thresholds led to no reduction below the 35 day/year limit, whereas it would fall below if the identified DD days were used. The general agreement and disagreement with the evaluation of identified DD days is given as contingency table (see columns 6 to 10 in Table 4), while evaluations of the single days are given in the supplement (Table S1). In total 16 days (6.6%) were identified as true positive (TP) DD days, whereas 184 days (76.0%) were identified as true negatives (TN). This means, that 82% of the days exceeding the daily limit were correctly classified in DD and non-DD days using the thresholds. Regarding the remaining days, five days (2%) were identified as false positive (FP) DD days, while 34 days (13.6%) were found to be false negatives. For 20 of these days some uncertainty of the classification of DD days based on model and \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline  & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** \\ \hline \multirow{3}{*}{**Year**} & \multirow{3}{*}{
\begin{tabular}{c} **PM\({}_{\mathrm{10}}\)** **DB** \\ **\(>\)**50\(\mathrm{\mu g/m^{3}}\)** \\ **\end{tabular} } & **Identified** & **PM\({}_{\mathrm{10}}\)**DB** & **Estimated** & **PM\({}_{\mathrm{10}}\)**DB** & **Estimated** & **PM\({}_{\mathrm{10}}\)**DB** & **Estimated** & **PM\({}_{\mathrm{10}}\)**DB** & **FIP** & **FN** & **NAs** \\  & & **DD Days** & **50\(\mathrm{\mu g/m^{3}}\)** & **DD Days** & **50\(\mathrm{\mu g/m^{3}}\)** & **DP Days** & **50\(\mathrm{\mu g/m^{3}}\)** & **TP** & **TN** & **FP** & **FN** & **NAs** \\  & & **(GDD)** & **10D Days** & **(eDD)** & **eDD Days** & & & & & \\ \hline
2013 & 44 & 8 (4) & 40 & 6 (5) & 39 & 3 & 32 & 3 & 4 & 2 \\
2014 & 27 & 10 (7) & 20 & 4 (4) & 23 & 4 & 17 & 0 & 6 & 0 \\
2015 & 39 & 10 (5) & 34 & 3 (3) & 36 & 3 & 28 & 0 & 7 & 1 \\
2016 & 39 & 2 (2) & 37 & 2 (2) & 37 & 2 & 37 & 0 & 0 & 0 \\
2017 & 54 & 11 (1) & 53 & 0 (0) & 54 & 0 & 43 & 0 & 10 & 1 \\
2018 & 39 & 10 (1) & 38 & 6 (1) & 38 & 4 & 27 & 2 & 6 & 0 \\ \hline Sum & 242 & 51 (20) & 222 & 21 (15) & 227 & 16 & 184 & 5 & 33 & 4 \\  & & & & & (6.6\%) & (76.0\%) & (2.1\%) & (13.6\%) & (1.7\%) \\ \hline \end{tabular}
\end{table} 
Table 4: Column 1: Amount of days of PM\({}_{\mathrm{10}}\) exceedance at DB, Column 2: Identified desert dust days (iDD), amount of DD days leading to a reduction below 50 \(\mathrm{\mu g/m^{3}}\) shown in brackets, Column 3: Remaining days exceeding the daily limit after deduction of the \(\mathrm{NDL_{MB}}\) on estimated DD days Column 6–10: Contingency table (TP = true positives, TN = true negatives, FP = false positives, FN = false negatives, NAs = no PM\({}_{\mathrm{10}}\) data from Masenberg available). trajectory analysis remains, i.e., the visualizations showed slightly different results or the influence can be expected to be very small. The other 14 days show a clear influence of DD. Still all 34 days need further investigations, as this classification as false negatives could easily be an effect of the systematic error introduced by our calculation of the BGL. Adjusting the calculation procedure for every DD event could overcome this limitation, but this adjustment could also make the identification of DD days slightly more subjective. For 15 out of these 34 days the NDL\({}_{\text{MB}}\) was below 2 ug/m\({}^{3}\) while PM\({}_{10}\) concentrations at DB ranged from 51 to 139 ug/m\({}^{3}\) with a mean value of 64 ug/m\({}^{3}\), indicating on one hand that DD is not the main influence on PM\({}_{10}\) concentrations at this site, on the other hand that an increase of NDL\({}_{\text{MB}}\) via a reduction of the BGL would allow to reach a reduction below the daily limit value in single cases.