Xu Chen , Jiayu Rong, Junxuan Fan, Renbin Zhan , Charles E. Mitchell, David A.T. Harper, Michael J. Melchin, Ping'an Peng, Stan C. Finney, and Xiaofeng Wang. Episodes 2006;29:183-96. https://doi.org/10.18814/epiiugs/2006/v29i3/004

Incomplete understanding of the sources of secondary organic aerosol (SOA) leads to large uncertainty in both air quality management and in climate change assessment. Chemical reactions occurring in the atmospheric aqueous phase represent an important source of SOA mass, yet, the effects of anthropogenic emissions on the aqueous SOA (aqSOA) are not well constrained. Here we use compound-specific dual-carbon isotopic fingerprints (δ¹³C and Δ¹⁴C) of dominant aqSOA molecules, such as oxalic acid, to track the precursor sources and formation mechanisms of aqSOA. Substantial stable carbon isotope fractionation of aqSOA molecules provides robust evidence for extensive aqueous-phase processing. Contrary to the paradigm that these aqSOA compounds are largely biogenic, radiocarbon-based source apportionments show that fossil precursors produced over one-half of the aqSOA molecules. Large fractions of fossil-derived aqSOA contribute substantially to the total water-soluble organic aerosol load and hence impact projections of both air quality and anthropogenic radiative forcing. Our findings reveal the importance of fossil emissions for aqSOA with effects on climate and air quality.

Many large paleo-lakes in North China were formed after the Triassic Era. Seawater incursion events (SWIEs) in these lakes have been extensively discussed in the literature, yet lack reliable methodology and solid evidence, which are essential for reconstructing and confirming SWIEs. The present study employs specific marine biological markers (24-n-propyl and 24-isopropyl cholestanes) to trace SWIEs in a dated core taken from the Songliao Basin (SLB). Two SWIEs were identified. The first SWIE from 91.37 to 89.00 Ma, was continuous and variable but not strong, while the second SWIE from 84.72 to 83.72 Ma was episodic and strong. SWIEs caused high total organic carbon (TOC) and negative δ¹³C_orgvalues in the sediments, which were interpreted as an indication of high productivity in the lake, due to the enhancement of nutrient supplies as well as high levels of aqueous CO₂, due to the mixing of alkaline seawater and acidic lake water. The SWIEs in SLB were controlled by regional tectonic activity and eustatic variation. Movement direction changes of the Izanagi/Kula Plate in 90 Ma and 84 Ma created faults and triggered SWIEs. A high sea level, from 90 to 84 Ma, also facilitated the occurrence of SWIEs in SLB.

X-ray photoelectron spectroscopy (XPS) is a powerful technique for determining the surface chemical composition of atmospheric particles. In this article, we employed XPS to study atmospheric particles collected from Guangzhou city in typical sites and seasons. The results showed that the weight percentage of carbon, oxygen, nitrogen, and sulfur were about 70.5–87.1%, and these species dominated the surface structure of the particles independent of the collection site and season. Inorganic elements including Si, Na, Ca, Cl, Fe, K, Al, and Cu were also found on the particle surfaces. The high-resolution XPS spectra revealed: (1) High aromatic and aliphatic C-H, and other oxidized carbons were found on the surface of particles. (2) The nitrogen species were characterized by pyridinic, pyrrolic/amide, quaternary type nitrogen functionalities, and nitrate groups, indicating that inorganic and organic N species are both important components of N-containing particles. (3) Sulfate and sulfone groups were also present on the surface and were important components. The oxidized groups of C, N, and S were higher in winter samples, consistent with the monsoon weather of Guangzhou in winter, which is favorable for the formation of oxidized species. A comparison between total and surface analyses showed that the surface of particles was relatively high in organic carbon, NO₃ ⁻, and SO₄ ²⁻, and the interior of particles was higher in NH₄ ⁺. These results provide information on the formation of aerosols, e.g., NH₄ ⁺ may act as a very important nucleus and organic carbon, NO₃ ⁻, and SO₄ ²⁻ coat the nuclei during particle growth.