# Simulation of Aerosol Evolution within Background Pollution for Nucleated Vehicle Exhaust via TEMOM
## 4 Results and Discussion  
The simulation results are shown through the sampling line shown in Figure 1. In the plane, the data are taken at a certain distance from the exhaust pipe, 0.1 m, 0.5 m, 2.0 m, 5.0 m. The nucleation rate has no value beyond the length greater than 1 m, so the sampling line distance of the nucleation rate is 0.1 m, 0.25 m, 0.5 m, 0.75 m. In the calculation process of nucleation rate, the upper and lower limits of nucleation rate are limited in order to ensure the correct value. The nucleation rate generally cannot break the upper limit. The lower limit can be considered to be approximately zero due to a difference of about 15 orders of magnitude from the normal value. The most detailed account of the process is to be found in the work of [PERSON] and [PERSON] (1996). Take the flow field without pollution in 2004 as an example, as shown in Figure 2, the speed of the flow field, \(m_{0}\), \(m_{1}\), and nucleation rate are shown in Figure 2. This study uses three years of data, and there are two situations each year. Six conditions need to be analyzed in one simulation. There are eight sampling lines in each situation, and each sampling line has five custom scalar quantities and eight custom physical quantities. There are 312 (\(6\times 4\times 13\)) cases of data that need to be classified and displayed. Quantitative analysis in two-dimensional figures is complicated. Other data will be organized and displayed according to conditions to facilitate the comparison of differences. In the following figure, the blue dotted line represents the data under the condition of no pollution, and the solid red line represents the data under the condition of pollution. The horizontal \(y\)-axis represents the vertical distance from the exhaust pipe on the sampling line, and the maximum is 3.15 m. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Boundary**} & \multirow{2}{*}{**Temperature (K)**} & \multirow{2}{*}{**Velocity (m/s)**} & \multirow{2}{*}{**Boundary Type**} & \multicolumn{5}{c}{**Boundary Value**} \\ \cline{5-8}  & & & & **S.1** & **S.2** & **S.3** & **S.4** & **S.5** \\ \hline inlet & 400 & 4.8 & Fixed value & 1 & 1000 & 0 & 0 \\ inlet wall & 350 & & Fixed flux & 0 & 0 & 0 & 0 \\ right & 300 & & Fixed value & 0.3 & 0 & 3.07 \(\times\) 1000 & 3.65 \(\times\) 1000 & 4.42 \(\times\) 1002 \\ up (down) & 300 & & Fixed value & 0.3 & 0 & 3.07 \(\times\) 1000 & 3.65 \(\times\) 1000 & 4.42 \(\times\) 1002 \\ left & 300 & & Fixed value & 0.3 & 0 & 3.07 \(\times\) 1000 & 3.65 \(\times\) 1000 & 4.42 \(\times\) 1002 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Example boundary setting of nonpolluted 2004. As Figure 3 shows, in three years, the \(m_{0}\) under nonpolluted conditions on each sampling line is greater than the \(m_{0}\) under polluted conditions. [PERSON] and [PERSON] once discovered this phenomenon and gave a qualitative explanation [18]. [PERSON]'s work focuses on measured data. The work only analyzes the result of quantity concentration but does not analyze how the various processes have an integrated effect. The initial value in Table 2, \(m_{0}\) under no polluted conditions is already more significant than that under polluted conditions. The right end of Figure 3 is the value at the boundary,that is, the environmental value. Except for the apparent difference in 2004, the two lines overlapped in the other two years. However, at the left end of the figure, this difference is significantly larger than the difference in the environment. Vehicle emissions will promote the difference in background aerosols. That is, the number concentration under non-polluting conditions is greater than the number concentration under pollution conditions. In the process of aerosol evolution, nucleation and coagulation will affect the number concentration of particulate matter. Nucleation will increase the number concentration of particulate matter, and aggregation will reduce particulate matter concentration.