Assessment of Secondary Organic Carbon in the Southeastern United States: A Review

摘要

Organic carbon (OC) is one of the major components of ambient PM_2.5 (particulate matter [PM] ≤2.5 μm in aero-dynamic diameter) and a significant portion of OC is from secondary organic aerosol (SOA) formation in the south-eastern United States. Various approaches (based on mea-surement and modeling results) are applied to estimate secondary organic carbon (SOC) and its origins in the region. SOC estimates by various methods are consistent as to clear seasonal variation (i.e., relatively higher SOC in summer) and little spatial variability (i.e., a regional char-acteristic of SOC). However, there are differences as to the origins of SOC. SOA organic tracer and emission-based modeling studies indicate that the biogenic origin of SOC is dominant in the Southeast, showing that biogenic-origin SOC accounts for 90% of SOC in summer and more than 70% even in other seasons. However, results from other studies suggest that the anthropogenic origin of SOC is dominant, significant amounts of anthropogenic-origin SOC, or important roles of anthropogenic pollut-ants for SOA formation, especially at urban areas, as strong correlations between water-soluble OC (an indica-tor of SOC) and anthropogenic pollutants, considerable amounts of fossil water-soluble OC, and significant con-tributions of fossil SOC (37-52% in summer months, 70-73% in winter months) are observed. Therefore, more studies are needed to reconcile the differences in the source attribution of SOC measurements.