Biogenic Carbon and Anthropogenic Pollutants Combine to Form a Cooling Haze over the Southeastern US
Abstract
Remote sensing data over North America documents the ubiquity of secondary aerosols resulting from a combination of primary biogenic and anthropogenic emissions. The spatial and temporal distribution of aerosol optical thickness (AOT) over the southeastern United States (SE US) cannot be explained by sulfate aerosols alone, but is consistent with the spatial and seasonal distribution as well as the temperature dependence of natural biogenic volatile organic compound (BVOC) emissions. These patterns, together with observations of organic aerosol in this region being dominated by modern 14°C, indicate non-fossil fuel origins of the aerosols and strongly suggest the dominant AOT signal is due to secondary aerosol formed from BVOC oxidation. In addition, the AOT of the SE US possesses a weekly cycle with 30% higher AOT on weekdays, pointing to an anthropogenic contribution, likely associated with higher diesel truck emissions. A link between vehicular and biogenic emissions forming secondary aerosols that dominate the regional AOT is supported by recent measurement of organosulfates in aerosols formed by BVOC oxidation in a NOx and sulfate rich environment, or by more rapid oxidation of BVOC and formation of secondary aerosol under higher NOx conditions. Even though ground based measurements from the IMPROVE network suggest higher sulfate than organic concentrations near the surface in this region, we infer that much of the secondary organic aerosol in the southeast must occur above the surface layer, consistent with reported observations of the organic fraction of the total aerosol increasing with height. The observed AOT is large enough in summer to provide regional cooling; thus we conclude that this secondary aerosol source is climatically relevant with significant potential for a regional negative climate feedback as BVOC emissions increase with temperature.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A54D..04G
- Keywords:
-
- 0345 Pollution: urban and regional (0305;
- 0478;
- 4251)