Secondary organic aerosol yields from cloud-processing of isoprene oxidation products

While there is a growing understanding from laboratory studies of aqueous phase chemical processes that lead to secondary organic aerosol (SOA) formation in cloud droplets (SOA(drop)), the contribution of aqueous phase chemistry to atmospheric SOA burden is yet unknown. Using a parcel model including a multiphase chemical mechanism, we show that SOA(drop) carbon yields (Y-c) from isoprene (1) depend strongly on the initial volatile organic lcarbon (VOC)/NOx ratio resulting in 42% > Y-c > 0.4% over the atmospherically-relevant range of 0.25 < VOC/NOx < 100; (2) increase with increasing cloud-contact time; (3) are less affected by cloud liquid water content, pH, and droplet number. (4) The uncertainty associated with gas/particle-partitioning of semivolatile organics introduces a relative error of -50% <= Delta Y-c < + 100%. The reported yields can be applied to air quality and climate models as is done with SOA formed on/in concentrated aerosol particles (SOA(aer)).