# Summertime Aerosol Radiative Effects and Their Dependence on Temperature over the Southeastern USA
## 2 Methodology
### Aerosol-Climate Model  
In this study, the contribution of biogenic sources to the temperature dependence of the AOD over the southeastern USA was also assessed using the development version of the global aerosol-climate model ECHAM-HAMMOZ [31; 32; 33; 34; 35], version ECHAM6.1-HAM2.2-SALSA. The atmospheric circulation model ECHAM solves the fundamental equations for the atmospheric flow, physics and tracer transport. The aerosol model HAM takes advantage of the Sectional Aerosol module for Large-Scale Applications (SALSA), which was used to calculate the aerosol microphysics [33; 35; 52]. SALSA describes the aerosol population consisting of sulphate (SO\({}_{4}\)), sea salt, organic carbon (OC), black carbon (BC), mineral dust, and water, and uses seven size sections with moving centres to cover the size range from 3 nm to 10 \(\upmu\)m. External mixing of the aerosol particles was tracked with seven additional sections. Anthropogenic aerosol emissions were described with AeroCom-II Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) data [53; 54]. For biomass burning emissions, the Global Fire Emissions Database (GFEDv2; [55]) was used. Annual and monthly averages were used for the anthropogenic and biomass burning emissions, respectively. The activation of aerosol particles into cloud droplets was calculated with the semi-empirical parameterization of [PERSON] (1997) [56]. In our implementation of SOA formation in ECHAM-HAMMOZ, organic mass is emitted both as primary organic matter (POM) and in the form of volatile organic compounds (VOC). Here we consider xylene (XYL), toluene (TOL), and benzene (BENZ) as anthropogenic VOCs, which are entered into the model based on the AeroCom II ACCMIP emission inventories [53; 54]. BVOC emissions are computed online using the Model of Emissions of Gases and Aerosols from Nature (MEGAN, [57]). In our implementation, isoprene (ISOP) and monoterenes (MTP) are considered for BVOC emissions. POM is emitted only from anthropogenic sources and wildfires. Once emitted, all VOCs are subject to gas-phase oxidation. Here we consider the hydroxyl radical (OH) and ozone (O\({}_{3}\)) as daytime oxidants and nitrate radical (NO\({}_{3}\)) as a night time oxidant. The concentrations of OH, O\({}_{3}\) and NO\({}_{3}\) are prescribed with pre-computed climatological 3D fields from the MOZART model [58]. The applied reaction coefficients are listed in Table 2 and the reaction equation is given in the table caption. The oxidation products are grouped into two categories, the first of which contains semi- and non-volatile compounds that partition onto aerosols directly from the gas phase. The second category contains organic compounds that form SOA through aqueous phase chemistry. The compounds in the first category are grouped according to their volatility using the volatility basis set (VBS) approach [59; 60]. In our implementation we group them into three volatility \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**OH**} & \multicolumn{2}{c}{**O\({}_{3}\)**} & \multicolumn{2}{c}{**NO\({}_{3}\)**} \\ \cline{2-7}  & \(\mathbf{k_{0}}\) & \(\mathbf{E^{\prime}_{a}}\) & \(\mathbf{k_{0}}\) & \(\mathbf{E^{\prime}_{a}}\) & \(\mathbf{k_{0}}\) & \(\mathbf{E^{\prime}_{a}}\) \\ \hline XYL & \(2.31\times 10^{-11}\) & \(0\) & \(0.0\) & \(0\) & \(2.6\times 10^{-16}\) & \(0\) \\ TOL & \(1.81\times 10^{-12}\) & \(338\) & \(0.0\) & \(0\) & \(0.0\) & \(0\) \\ BENZ & \(2.33\times 10^{-12}\) & \(-193\) & \(0.0\) & \(0\) & \(0.0\) & \(0\) \\ ISOP & \(2.7\times 10^{-11}\) & \(390\) & \(1.03\times 10^{-14}\) & \(-1995\) & \(3.15\times 10^{-12}\) & \(-450\) \\ MTP & \(1.2\times 10^{-11}\) & \(440\) & \(6.3\times 10^{-16}\) & \(-580\) & \(1.2\times 10^{-12}\) & \(490\) \\ GLYX & \(0.0\) & \(0\) & \(0.0\) & \(0\) & \(6.0\times 10^{-13}\) & \(-1900\) \\ IEPOX & \(3.56\times 10^{-11}\) & \(0\) & \(0.0\) & \(0\) & \(0.0\) & \(0\) \\ \hline \hline \end{tabular}
\end{table}