# Effects of Aerosols on Gross Primary Production from Ecosystems to the Globe
## 3 Results
### Impact of Aerosols on GPP  
The impact of aerosols on GPP (\(\Delta\)GPP = \(\pm\)400 g C m\({}^{-2}\) yr\({}^{-1}\)) showed spatial heterogeneity on a global scale (Figure 6a). Aerosols had positive effects on GPP in many areas across the globe, such as northern China, Central Asia, India, Europe, tropical and southern Africa, and Mexico, and the positive impact of \(\Delta\)GPP could be up to 300\(-\)400 g C m\({}^{-2}\) yr\({}^{-1}\) (6-8%) (Figure 6a,c). The negative effects of aerosols on GPP were mainly concentrated in tropical Asia, western Europe, Amazon, and coastal areas in some regions (Figure 6a). From the perspective of latitude distribution, aerosols had a large weakening effect on \(\Delta\)GPP (200 g C m\({}^{-2}\) yr\({}^{-1}\)) in tropical and high latitude (220 g C m\({}^{-2}\) yr\({}^{-1}\)) regions but had a large enhancement effect for most subtropical (110 g C m\({}^{-2}\) yr\({}^{-1}\)) and temperate (80 g C m\({}^{-2}\) yr\({}^{-1}\)) regions (Figure 6b,d). From the percentage change in the spatial distribution of GPP caused by the aerosol, it was found that there was a large substantial increase in  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**EC-LUE**} & \multicolumn{3}{c}{**AOD-LUE**} \\ \hline
**Vegetation Types** & **Abbreviation** & **R\({}^{2}\)** & **RMSE** & **SD** & **R\({}^{2}\)** & **RMSE** & **SD** \\ \hline Crop & CRO & 0.78 *** & 3.04 & 6.20 & 0.80 *** & 2.97 & 5.64 \\ Closed Shrub & CSH & 0.18 ** & 2.76 & 1.88 & 0.29 ** & 2.59 & 1.69 \\ Deciduous Broadleaf Forest & DBF & 0.79 *** & 2.79 & 5.78 & 0.81 *** & 2.77 & 5.23 \\ Evergreen Broadleaf Forest & EBF & 0.35 ** & 2.21 & 2.07 & 0.45 ** & 2.09 & 1.87 \\ Evergreen Needleleaf Forest & ENF & 0.61 *** & 1.79 & 2.03 & 0.66 *** & 1.73 & 1.86 \\ Grassland & GRA & 0.72 *** & 2.82 & 3.26 & 0.76 *** & 2.71 & 2.95 \\ Mixed Forest & MF & 0.71 *** & 1.91 & 3.05 & 0.77 *** & 1.75 & 2.68 \\ Open Shrub & OSH & 0.65 ** & 0.66 & 0.81 & 0.68 *** & 0.59 & 0.74 \\ Wetlands & WET & 0.68 *** & 2.40 & 4.51 & 0.72 *** & 2.21 & 4.14 \\ Woody Savanna & WSA & 0.63 *** & 1.60 & 1.80 & 0.67 *** & 1.46 & 1.65 \\ \hline \hline \end{tabular}  
* * \(p\) <0.001; ** 0.001\(\leq p<\) 0.01 (2-tailed).  
\end{table}
Table 1: The performance of AOD-LUE and EC-LUE in simulating GPP for each vegetation type.  
Figure 5: (**a**) Comparison of GPP (g C m\({}^{-2}\) day\({}^{-1}\)) calculated by EC-LUE model and AOD-LUE model with GPP based on EC flux towers. The dotted red line shows the intersection of the two models. (**b**) illustrates how the AOD-LUE model compares with the EC-LUE model when the changed percentage value of R\({}^{2}\) ((AOD-LUE \(-\) EC-LUE)/EC-LUE) \(\times\) 100) varies with the R\({}^{2}\) value of the EC-LUE model.  
Different terrestrial ecosystems responded differently to aerosols (Figure 7). Among all vegetation types, aerosols had a positive impact of 2.38% on \(\Delta\)GPP and a negative impact of 3.83%. The GPP increased for some subtropical and temperate vegetation, some drought-tolerant woods and dry grasslands, but decreased for other vegetation types, including tropical vegetation and alpine vegetation (Figure 7). Specifically, there was a negative correlation between \(\Delta\)GPP and aerosols in Evergreen Broadleaf Forest (EBF) (\(-\)6.45%), Evergreen Broadleaf Forest (EBF) (\(-\)3.97%), Evergreen Needleleaf Forest (ENF) (\(-\)3.36%) and Wetlands (WET) (\(-\)4.67%). Aerosol positively influenced \(\Delta\)GPP in the mainly Grassland (GRA) (3.19%) and Deciduous Broadleaf Forest (DBF) (2.63%), graminoid and Open Shrub (OSH) (2.38%), Crop (CRO) (2.19%) and Woody Savanna (WSA) (1.49%).  
Figure 6: The spatial distribution of aerosol effects on global (**a**) \(\Delta\)GPP (g C m\({}^{-2}\) yr\({}^{-1}\)) and the variation of its annual (**b**) latitude from 2000 to 2019.The percentage changes in the spatial distribution of (**c**) \(\Delta\)GPP (%) (GPP(AOD-LUE) \(-\) GPP(EC-LUE)/GPP(EC-LUE) \(\times\) 100) caused by aerosols and the variation of its (**d**) latitude from 2000 to 2019.