## 2 Materials and Method
### The Seven Aging Schemes  
In the present simulations, we considered seven organic aerosol aging parameterizations, taking into account three different functionalization schemes, two biogenic SOA aging schemes and also different fragmentation probabilities. These parameterizations have been described in detail by [PERSON] et al. [20] and they were determined to have the best performance in the OA simulations in the Po Valley in Italy. In the simulations here, the same parameterizations will be used to test their robustness when applied in a very different environment, i.e., the boreal forest in Finland. Table 1 summarizes the seven parameterizations that were used in the simulations.  
Figure 1: **(a)** The ensemble of 20 trajectories calculated by HYSPLIT for air parcels arriving at the site of Hyytialä on 7 May 2013 at 15:00 LT and **(b)** the ensemble average trajectory calculated by the HYSPLIT clustering utility.  
The first set of simulations use the simple functionalization scheme (1-bin case), which assumes a one-volatility-bin reduction for every reaction with OH with a simultaneous increase in oxygen atoms, with a probability of 50% for an increase of one oxygen atom and 50% probability for an increase of two oxygen atoms. It also assumes negligible additional production of bSOA during aging (no bSOA aging) and no fragmentation of the organic compounds. Implicitly, this scheme assumes that the functionalization represents the net effect of these pathways.  
The second set of simulations (1-bin/bSOA/b = 0.15 case) explores the role of fragmentation for the 1-bin simple functionalization scheme, assuming addition/production of bSOA during aging and combined with the fragmentation parameterization with the fragmentation probability equal to 15% as estimated previously [20].  
The third set of simulations (2-bin case) uses the second simple functionalization scheme, where a two-volatility bin reduction is assumed for every reaction with a simultaneous increase in oxygen atoms. A 50% probability for the increase of one oxygen atom and 50% probability for the increase of two oxygen atoms are used similarly to the 1-bin case. Finally, there is no addition or production of bSOA, and fragmentation is neglected in this model.  
The fourth set of simulations (2-bin/\(b\) = 0.1 case) uses the 2-bin functionalization scheme, neglecting bSOA aging and assuming now a fragmentation probability equal to \(b\) = 0.1 (10%) as estimated [20]. The fifth set of simulations (2-bin/bSOA/\(b\) = 0.4 case) uses the 2-bin functionalization, with the assumption of bSOA aging and more rapid fragmentation (\(b\) = 0.4).  
In the sixth set of simulations, a more rigorous functionalization is explored, initially suggested by [PERSON] et al. [16], and which is called the detailed functionalization scheme. In this scheme, there is a 30% probability of adding one O atom, a 50% probability of adding two O atoms, and a 20% probability of adding three O atoms. Each addition of O atoms results in a different distribution of volatility reductions, with an average reduction of \(-1.75\) in log\({}_{10}\)C* per oxygen added. It also assumes negligible additional production of bSOA during aging (no bSOA aging) and assumes a fragmentation probability equal to 30%, as estimated from the simulations in the Po Valley [20]. This case is called the DET/\(b\) = 0.3 case.  
In the seventh and last simulation, the detailed functionalization, bSOA aging and intense fragmentation (\(b\) = 0.7) are assumed, and the case is called DET/bSOA/\(b\) = 0.7 case, as suggested by [PERSON] et al. [20].