|Title||Radiative forcing of organic aerosol in the atmosphere and on snow: Effects of SOA and brown carbon|
|Publication Type||Journal Article|
|Year of Publication||2014|
|Authors||Lin G.X, Penner JE, Flanner M.G, Sillman S., Xu L, Zhou C|
|Journal||Journal of Geophysical Research-Atmospheres|
|Type of Article||Article|
|Keywords||alpha-pinene; black carbon; complex refractive-index; global-model; glyoxal uptake; intercomparison project accmip; light-absorption; optical-properties; spectral dependence; substances hulis|
Organic aerosols (OA) play an important role in climate change. However, very few calculations of global OA radiative forcing include secondary organic aerosol (SOA) or the light-absorbing part of OA (brown carbon). Here we use a global model to assess the radiative forcing associated with the change in primary organic aerosol (POA) and SOA between present-day and preindustrial conditions in both the atmosphere and the land snow/sea ice. Anthropogenic emissions are shown to substantially influence the SOA formation rate, causing it to increase by 29 Tg/yr (93%) since preindustrial times. We examine the effects of varying the refractive indices, size distributions for POA and SOA, and brown carbon fraction in SOA. The increase of SOA exerts a direct forcing ranging from -0.12 to -0.31W m(-2) and a first indirect forcing in warm-phase clouds ranging from -0.22 to -0.29W m(-2), with the range due to different assumed SOA size distributions and refractive indices. The increase of POA since preindustrial times causes a direct forcing varying from -0.06 to -0.11W m(-2), when strongly and weakly absorbing refractive indices for brown carbon are used. The change in the total OA exerts a direct forcing ranging from -0.14 to -0.40W m(-2). The atmospheric absorption from brown carbon ranges from +0.22 to +0.57W m(-2), which corresponds to 27%similar to 70% of the black carbon (BC) absorption predicted in the model. The radiative forcing of OA deposited in land snow and sea ice ranges from +0.0011 to +0.0031W m(-2) or as large as 24% of the forcing caused by BC in snow and ice simulated by the model.