Fossil and Nonfossil Sources of Organic and Elemental Carbon Aerosols in the Outflow from Northeast China

Source quantification of carbonaceous aerosols in the Chinese outflow regions still remains uncertain despite their high mass concentrations. Here, we unambiguously quantified fossil and nonfossil contributions to elemental carbon (EC) and organic carbon (OC) of total suspended particles (TSP) from a regional receptor site in the outflow of Northeast China using radiocarbon measurement. OC and EC concentrations were lower in summer, representing mainly marine air, than in other seasons, when air masses mostly traveled over continental regions in Mongolia and northeast China. The annual-mean contribution from fossil-fuel combustion to EC was 76 ± 11% (0.1–1.3 μg m^–3). The remaining 24 ± 11% (0.03–0.42 μg m^–3) was attributed to biomass burning, with slightly higher contribution in the cold period (∼31%) compared to the warm period (∼21%) because of enhanced emissions from regional biomass combustion sources in China. OC was generally dominated by nonfossil sources, with an annual average of 66 ± 11% (0.5–2.8 μg m^–3), approximately half of which was apportioned to primary biomass-burning sources (34 ± 6%). In winter, OC almost equally originated from primary OC (POC) emissions and secondary OC (SOC) formation from fossil fuel and biomass-burning sources. In contrast, summertime OC was dominated by primary biogenic emissions as well as secondary production from biogenic and biomass-burning sources, but fossil-derived SOC was the smallest contributor. Distinction of POC and SOC was performed using primary POC-to-EC emission ratios separated for fossil and nonfossil emissions

Radiocarbon-Based Source Apportionment of Carbonaceous Aerosols at a Regional Background Site on Hainan Island, South China

To assign fossil and nonfossil contributions to carbonaceous particles, radiocarbon (¹⁴C) measurements were performed on organic carbon (OC), elemental carbon (EC), and water-insoluble OC (WINSOC) of aerosol samples from a regional background site in South China under different seasonal conditions. The average contributions of fossil sources to EC, OC and WINSOC were 38 ± 11%, 19 ± 10%, and 17 ± 10%, respectively, indicating generally a dominance of nonfossil emissions. A higher contribution from fossil sources to EC (∼51%) and OC (∼30%) was observed for air-masses transported from Southeast China in fall, associated with large fossil-fuel combustion and vehicle emissions in highly urbanized regions of China. In contrast, an increase of the nonfossil contribution by 5–10% was observed during the periods with enhanced open biomass-burning activities in Southeast Asia or Southeast China. A modified EC tracer method was used to estimate the secondary organic carbon from fossil emissions by determining ¹⁴C-derived fossil WINSOC and fossil EC. This approach indicates a dominating secondary component (70 ± 7%) of fossil OC. Furthermore, contributions of biogenic and biomass-burning emissions to contemporary OC were estimated to be 56 ± 16% and 44 ± 14%, respectively

Source Apportionment Using Radiocarbon and Organic Tracers for PM_2.5 Carbonaceous Aerosols in Guangzhou, South China: Contrasting Local- and Regional-Scale Haze Events

We conducted a source apportionment and investigated the atmospheric behavior of carbonaceous aerosols during hazy and normal days using radiocarbon (¹⁴C) and biomass burning/secondary organic aerosol (SOA) tracers during winter in Guangzhou, China. Haze episodes were formed either abruptly by local emissions or through the accumulation of particles transported from other areas. The average contributions of fossil carbon to elemental carbon (EC), water-insoluble organic carbon, and water-soluble organic carbon were 71 ± 10%, 40 ± 6% and 33 ± 3%, respectively. High contributions of fossil carbon to EC (80–90%) were observed for haze samples that were substantially impacted by local emissions, as were the highest (lowest) ratios for NO₃^–/SO₄^2– (OC/EC), which indicates that these particles mainly came from local vehicle exhaust. Low contributions of fossil carbon to EC (60–70%) were found for haze particles impacted by regional transport. Secondary organic carbon (SOC) calculated using SOA tracers accounts for only ∼20% of the SOC estimated by ¹⁴C, which is probably because some important volatile organic carbons are not taken into account in the SOA tracer calculation method and because of the large discrepancy in ambient conditions between the atmosphere and smog chambers. A total of 33 ± 11% of the SOC was of fossil origin, a portion of which could be influenced by humidity