## 3 Results
### Atmospheric Investigation
#### 3.2.2 Atmospheric Composition Investigation (SO\({}_{2}\), DMS, Aerosol and CO)
On the other hand, Figure 15A (25 March 2021) and Figure 15B (18 May 2021) show high concentrations in the Canarias volcano caldera, even if the La Palma volcano does not seem to observe particularly high concentrations. The aerosol distribution reported in Figure 15D,E (12 July 2021 at 13 and 23 UT) suggest that around the volcano, the aerosol was lower, and it is difficult to think that it is produced by the volcanic activity, even if it cannot be excluded some indirect phenomena. Figure 16 shows the carbon monoxide time series in the six months preceding \"La Palma\" volcano eruption. CO presents several anomalous values, and maps of some of them are represented in Figure 17. It is also interesting to note that from the end of July, the CO trend seems to increase with respect to the typical historical value, as we marked  
Figure 12: Dimethyl Sulphide (DMS) time series in the six months before La Palma volcano eruption. The values are extracted at 23 UT. Figure 13: Distribution maps of the DMS for one of each of the three groups of anomalous days depicted by the time series around La Palma volcano (represented by a white star). The values are extracted at 23 UT. with the black dot bold arrow in Figure 16. Investigating the maps, it is possible to exclude a volcano source for the 19 April and 2 August anomalies, while the other days could be related to the volcanic activity but still not directly emitted from the volcano. In particular, the values of 25 March and 14 September 2021 are spatially closer to the volcano and Canarias caldera. Figure 14: Aerosol time series in the six months before La Palma volcano eruption. The values are extracted at 23 UT. 1990, 2002, and 2020 have been automatically excluded from the analysis due to the presence of outliers. Figure 15: Distribution maps of the aerosol for some representative days of the various groups of anomalies depicted by the time series: (**A**) 25 March 2021, 23 UT, (**B**) 18 May 2021, 23 UT, (**C**) 9 June 2021, 23 UT, (**D**) 12 July 2021, 13 UT, (**E**) 12 July 2021, 23 UT, and (**F**) 15 August 2021, 23 UT. On the day of the eruption, only SO2, CO, and aerosol presented particularly high values, as shown in Figure 18 and Figure S4 (in Supplementary Materials File S1), while DMS showed normal values above la Palma. In Figure 18A, we identified the start of the emission of SO2 around 9 UT, even if in the hours before there was an almost-continuous emission but with a lower intensity. The start of emission of carbon monoxide seems later at about 11 UT, as shown in Figure 18C. Both the parameters reached the maximum concentrations at 17 UT, as depicted in Figure 18B,D. It is possible to note that the maximum concentrations of SO2 are not affected by the presence of outliers. Figure 11:0 Carbon monoxide time series in the six months before La Palma volcano eruption. The values are extracted at 23 UT. The years 2010, 2012, and 2016 have been automatically excluded from the analysis due to the presence of outliers. Figure 11:1 Distribution maps of the CO for some representative days of the various groups of anomalies depicted by the time series. The values are extracted at 23 UT. value is about ten times higher than previous maps, i.e., the typical value. This high concentration is very likely due to the volcano's eruption, and we expect it to be much more intense than possible pre-eruption emissions. Figure 19 represents the daily mean value of SO\({}_{2}\), dimethyl sulphide (DMS), aerosol, and CO inside a 3 degrees side square box centred on the volcano. A linear fit has been computed to estimate an eventual trend of \"global warming\", although the obtained slopes are almost null for all parameters. This is probably because the selected parameters are not substantially affected by this phenomenon, like the temperature or the greenhouse gases such as methane and carbon dioxide, which instead show such a trend, as we found in previous works [52,81,82,83].