Terrestrial vegetation releases large quantities of plant volatiles into the atmosphere that can then oxidise to form secondary organic aerosol. These particles affect plant productivity via the diffuse radiation fertilisation effect through altering the balance between direct and diffuse radiation reaching the Earth’s surface. Here, using a suite of models describing relevant coupled components of the Earth system, we quantify the impacts of biogenic secondary organic aerosol on plant photosynthesis via this fertilisation effect. We show that this leads to a net primary productivity enhancement of 1.23 Pg C a-1 (range 0.75-1.62 Pg C a-1 due to uncertainty in biogenic secondary organic aerosol formation). Notably, this productivity enhancement is twice the mass of biogenic volatile organic compound emissions (and ~30 times larger than the mass of carbon in biogenic secondary organic aerosol) causing it. Hence, our simulations indicate that there is a strong positive ecosystem feedback between biogenic volatile organic compound emissions and plant productivity via plant-canopy light-use efficiency. We estimate a gain of 1.07 in global biogenic volatile organic compound emissions resulting from this feedback.