# Effects of Aerosols on Gross Primary Production from Ecosystems to the Globe
In addition, the negative effect of high-load aerosols on GPP is also manifested in that aerosol particles are deposited on leaves, thereby blocking stomata, directly affecting plant photosynthesis and related protein expression [10]. For example, a modeling study showed that for a part of the northern coniferous forest, a relatively high aerosol loading (AOD > 2) resulted in a decrease in total radiation and thereby the GPP [4]. Second, the effect of aerosols on GPP may also be limited to the height and leaf area index (LAI) and variations in different ecosystems. Increased diffuse radiation can enhance GPP for forests (i.e., broadleaf forest) with complex canopy structure and high LAI [13; 15; 16] but not for forests with low canopy (i.e., wetlands) and LAI (i.e., needleleaf forest) [17; 18]. However, few studies have currently considered both the regional differences in aerosol loading distribution and the differences in vegetation structure characteristics [19; 20; 21]. There is an urgent need to systematically study the specific impact of aerosols on GPP from a global perspective. Existing studies have proved that incorporating the impact of aerosols on GPP in the GPP models is an important and effective way to reduce the uncertainty of GPP estimates [22; 23; 24]. The transmission of direct light and diffuse light in the canopy can differ due to aerosols [25], and therefore some models need to divide the canopy into sunlit and shaded leaves [26; 27]. For example, some current two-leaf models and land surface process models [28; 29] consider the influence of aerosols and improve the performance in simulating GPP by calculating photosynthetically active radiation and GPP for shaded and sunlit leaves separately [30]. However, most of the current light use efficient (LUE) models treat the entire canopy as a leaf [31], ignoring the differences in photosynthetic active radiation (PAR) and LUE caused by aerosols among different leaves within the canopy [16; 32; 33]. Regional and global GPP estimates have substantial uncertainty partly because the influence of aerosol on radiation is not considered [34; 35; 36]. [PERSON] et al. [31] found that ignoring the promotion of aerosols on diffuse radiation (increasing the diffuse radiation by 43%) led to an underestimation of the European GPP. Therefore, we emphasize the need to quantify the relationship between aerosols and diffuse radiation, which is a factor that cannot be ignored in future GPP simulation improvements. In this study, we improved a widely used LUE model, EC-LUE, by including aerosol-radiation effects, and examined the potential impact of aerosols on GPP at a global scale. The EC-LUE is a widely used tool to estimate large-scale real GPPs because of its reasonable performance and few input parameters [37]. Data from the EC-sites and satellites were used to monitor GPP at the global scale and evaluate the impact of aerosols on it. The objectives of this study were: (1) to quantify the relationship between aerosols and diffuse radiation; (2) to determine whether aerosols and diffuse radiation can be included in the GPP model; and (3) to quantify the aerosol impact on GPP at the global scale.