## 3 Results and Discussion  
### Emission Factor of Tepenes  
Figure 3 shows the EF of isoprene increasing in the series: 11, 13, 15 and 17 h consistently for both species. The mean normalized EF obtained for _Platanus \(\times\) acerifolia_ was 20.62 \(\pm\) 18.41 \(\upmu\)g g\({}_{\text{ddw}}\)\({}^{-1}\) h\({}^{-1}\), in good agreement with the 18.5 \(\upmu\)g g\({}_{\text{ddw}}\)\({}^{-1}\) h\({}^{-1}\) reported by [PERSON] (2019) [22] in Sweden and 27 \(\pm\) 25.3 \(\upmu\)g g\({}_{\text{ddw}}\)\({}^{-1}\) h\({}^{-1}\) by [PERSON] et al. (2014) [23] for _Platanus orientalis_ in Turkey. [PERSON] et al. (2020) reported an EF for _Platanus occidentalis_ of 21.36 \(\upmu\)g g\({}_{\text{ddw}}\)\({}^{-1}\) h\({}^{-1}\) in Beijing [24]. [PERSON] et al. (2017) [18] obtained average emission values in a wide range from 1.5 to 45 \(\upmu\)g g\({}_{\text{ddw}}\)\({}^{-1}\) h\({}^{-1}\) for _P. orientalis_ depending on whether measurements were taken at the beginning or at the end of the season, respectively, in Iran, which may suggest a strong dependence of emissions on the season and variant of _Platanus_. The EF for _S. molle_, being consistent in trend with those of _P. \(\times\) acerifolia_, exhibited consistently lower values, ranging from a minimum of 1.1 \(\pm\) 0.8 \(\upmu\)g g\({}_{\text{ddw}}\)\({}^{-1}\) h\({}^{-1}\) to a  
Figure 3: Standardized emission factor of isoprene (EF) and the corresponding standard error expressed as \(\upmu\)g g\({}_{\text{ddw}}\)\({}^{-1}\) h\({}^{-1}\) for _Platanus \(\times\) acerifolia_ and _Schinus molle_ at different times of the day. maximum of 4.4 \(\pm\) 2.9 \(\mathrm{\SIUnitSymbolMicro g_{ldw}}^{-1}\) h\({}^{-1}\). Thus, the mean values of EF in _S. molle_ were 33.2%, 26.1%, 12.35% and 10.35% of those recorded for _P. \(\times\) accerifolia_ at 11:00, 13:00, 15:00 and 17:00 h, respectively (Figure 3). Terpenes other than isoprene contrasted strongly between _P. \(\times\) accerifolia_ and _S. molle_. First, _P. \(\times\) accerifolia_ emitted all 15 terpen measured other than isoprene while _S. molle_ only emitted nine (Figure 4). Second, emission factors for _S. molle_ were much greater than those of _P. \(\times\) accerifolia_ for those mono- and sesquiterpenes measured that exhibited any rate of emission for both species. Third, a marked diurnal variation was observed for some compounds also contrasting between species. Twelve monoterpens and two sesquiterpenes exhibited greater emissions in the morning, decreasing in the afternoon for _P. \(\times\) accerifolia_, which was in contrast to the behavior of normalized isoprene (Figure 3). For _S. molle_, this pattern was also observed for some terpen other than isoprene. Such pattern differences between isoprene, increasing during the day, and some terpen other than isoprene, decreasing during the day, are intriguing. We might speculate that isoprene depends mostly on cumulative radiative and temperature stresses, while terpen other than isoprene on metabolic activity which are higher at 11:00 am, with more favorable environmental conditions which become harsher later during the day. Another explanation could be that the monoterpens are synthesized and stored to be emitted when required to provide specific metabolic signals, unlike isoprene, which is synthesized and emitted immediately according to radiative and temperature stresses. The mean EF for total monoterpens and the two sesquiterpenes for _P. \(\times\) accerifolia_ was 0.11 \(\pm\) 0.03 \(\mathrm{\SIUnitSymbolMicro g_{ldw}}^{-1}\) h\({}^{-1}\). [PERSON] (2019) [22] reported an EF of total monoterpens between 0.1 and 3.9 \(\mathrm{\SIUnitSymbolMicro g_{ldw}}^{-1}\) h\({}^{-1}\) for _Platanus \(\times\) bispanica_ (or _P. \(\times\) accerifolia_). [PERSON] et al. (2014) [23] reported an EF of total monoterpens of 0.025 \(\pm\) 0.006 \(\mathrm{\SIUnitSymbolMicro g_{ldw}}^{-1}\) h\({}^{-1}\) for _P. orientalis_. The authors agree on the results for monoterpens, but not for isoprene in the case of _Platanus_. For _S.