Marine primary and secondary organic aerosols and their effect on indirect radiative forcing

Description

The effects of marine biogenic volatile organic compounds (BVOCs) and primary organic carbon aerosol emissions on microphysical properties of clouds were explored by conducting 10-year CAM5.0 model simulations at a grid resolution of 1.9°×2.5° with 30 vertical layers. The model-predicted relationship between ocean physical and biological systems and the abundance of cloud condensation nuclei (CCN) in remote marine atmosphere was compared to in situ measurements and data from the A-Train satellites. Model simulations show that on average, primary and secondary organic aerosol emissions from the ocean can yield up to a 5% increase in droplet number concentration of maritime shallow clouds and up to a 4% increase in liquid water path. Changes associated with cloud properties increase shortwave forcing over the oceans by -0.2 W/m2 and by -0.8 W/m2 over the Southern Ocean. By using different emission scenarios and droplet activation parameterizations, this study suggests that the addition of marine primary aerosols and biologically generated reactive gases makes an important difference in radiative forcing assessments.