According to the authors,
"The atmospheric aerosols could thus disturb solar radiation income and global climate through influencing the transfer of energy in the atmosphere in two ways (Hansen et al. 1997, Carslaw et al. 2013). On the one hand, the atmospheric aerosols can directly reflect and absorb the solar radiation in both the troposphere and stratosphere. On the other hand, the atmospheric aerosols could modify the optical properties of clouds through cloud condensation nuclei which lead to increase cloud droplet number concentrations, and thus affect the incoming radiation indirectly"
"The atmospheric aerosols play a dominant role in the global energy balance by contributing to a net reduction of 5 to 10% in solar energy received at the Earth's surface, therefore the dynamics of the atmospheric aerosol load is of vital importance for the science and policy of environmental pollution and global climate change"
A 5-10% decrease in solar energy received at the Earth's surface due to aerosols is huge [up to 136 W/m2], and far more than the ~0.5 W/m2 increase alleged due to man-made greenhouse gases since the beginning of the industrial revolution. A mere 1-2% change in global albedo from clouds/aerosols is sufficient to tip the balance between global warming or cooling.
"Our understanding of the global aerosol change is rather limited, although it is well known that aerosol forcing could affect the global radiative budget, hydrological processes, carbon, nitrogen and sulfur cycles, as well as climate change."Although aerosol emissions have been sharply curtailed and continue to decline in industrialized countries, little to no regulation is in place in developing countries, thus the authors find
"It is interesting to find that high concentrations of aerosols are mainly distributed in regions where developing countries are located (Asia and Africa), and an increasing trend could also be observed."