Global Distribution, Radiative Forcing, and Climate Impact of Carbonaceous Aerosols
This thesis is motivated by the need to better understand and quantify the climate effects of carbonaceous aerosols, i.e., black carbon (BC) and organic carbon (OC). Global three-dimensional distribution of carbonaceous aerosols is simulated online in a general circulation model (GCM). The carbona...
| Summary: | This thesis is motivated by the need to better understand and quantify the climate effects of carbonaceous aerosols, i.e., black carbon (BC) and organic carbon (OC). Global three-dimensional distribution of carbonaceous aerosols is simulated online in a general circulation model (GCM). The carbonaceous aerosol model includes primary BC, primary OC, five groups of biogenic volatile organic compounds (BVOCs), and fourteen semi-volatile products of BVOC oxidation by O3, OH, and NO3, which condense to form secondary organic aerosols (SOAs) based on an equilibrium partitioning model. Human activities since the preindustrial period are predicted to have increased global burdens of BC and OC by an order of magnitude and almost tripled the SOA production rate. Based on an older emission inventory for BC, the direct radiative forcing of increased atmospheric BC burden is estimated to warm the atmosphere by 0.51 to 0.8 W m<sup>-2</sup>, depending on how BC is mixed with other tropospheric aerosols. For OC, the estimated anthropogenic direct radiative forcing at top of the atmosphere (TOA) is -0.1 to -0.2 W m<sup>-2</sup>, depending on the water-uptake property of OC. When BC, OC and sulfate are combined, the estimated direct radiative forcing at TOA is -0.39 to -0.78 W m<sup>-2</sup>. Using an updated emission inventory, direct radiative forcing of anthropogenic BC at TOA is estimated to be +0.33 and +0.6 W m<sup>-2</sup>, for BC mixed externally and internally with present-day level of sulfate, respectively. Using a GCM coupled to a mixed-layer ocean model, these estimated forcings for BC are predicted to warm surface air temperature by 0.2 to 0.37 K. The temperature increase is the largest over northern high latitutdes during winter and early spring. Even though the predicted global-averaged warming due to BC is less than that of greenhouse gases, significant regional differences do exist, such as substantial warming in central and eastern Russia predicted for BC. In addition to temperature increase, direct radiative forcing of anthropogenic BC is also predicted to lead to a change in the hydrological cycle by shifting the intertropical convergence zone northward. |
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