Source apportionment using radiocarbon and organic tracers for PM2.5 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 ((14)C) 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 (14)C, 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.

The use of levoglucosan and radiocarbon for source apportionment of PM(2.5) carbonaceous aerosols at a background site in East China.

Samples of fine particulate matter (PM2.5) were collected during July 2009 to March 2010 at a regional background site in East China. The mass concentrations of organic carbon (OC) and elemental carbon (EC) were characterized by the highest levels in winter (December to February) and the lowest abundances in summer (June to August). Conversely, the concentrations of levoglucosan were higher in summer than in winter. The observations were associated to the anthropogenic air pollutions (predominantly fossil-fuel combustions) transport from the center and north China with the northwest winds in winter and large contribution of the open biomass burning activities in South China and East China in summer, which was evident by air-mass trajectories and MODIS satellite fire counts. To assign fossil and nonfossil contributions of carbonaceous matters, the radiocarbon contents in water-insoluble OC (WINSOC) and EC in 4 combined samples representing four seasons were analyzed using the isolation system established in China. The results indicated that biomass burning and biogenic sources (59%) were the major contribution to the WINSOC, whereas fossil fuel (78%) was the dominant contributor to the refractory EC at this site. The source variation obtained by radiocarbon was consistent with other indicators, such as the OC/EC ratios and the levoglucosan concentration. Biomass burning and biogenic emissions were found to predominate in the summer and autumn, whereas fossil fuel emissions predominate in winter and spring.

Dual carbon isotopes (14C and 13C) and optical properties of WSOC and HULIS-C during winter in Guangzhou, China.

Water-soluble brown carbon (ws-BrC) exerts an important influence on climate change, but its emission sources and optical properties remain poorly understood. In this study, we isolated two ws-BrC proxies, water-soluble organic carbon (WSOC) and humic-like substance carbon (HULIS-C), from particulate matter collected in Guangzhou, China, during December 2012 for the measurement of dual carbon isotopes (14C and 13C) and light absorption. The mass absorption efficiencies of WSOC and HULIS-C at 365nm were 0.81±0.16 and 1.33±0.21m2g-1C, respectively. The 14C results showed that two-thirds of WSOC and HULIS-C were derived from non-fossil sources (e.g., biomass burning and biogenic emission), and the remaining third was derived from fossil sources. The δ13C values of WSOC and HULIS-C were -23.7±1.2‰ and -24.2±0.9‰, respectively, underlining the limited influences of C4 plants and natural gas on ws-BrC. Fitting the data to a multiple linear regression, we further concluded that approximately 80% and 10% of the light absorption at 365nm was due to non-fossil and fossil carbon, respectively. Non-fossil sources of ws-BrC, such as the burning of agricultural residue, were responsible for the light absorption recorded in Guangzhou.

Sources, compositions, and optical properties of humic-like substances in Beijing during the 2014 APEC summit: Results from dual carbon isotope and Fourier-transform ion cyclotron resonance mass spectrometry analyses.

Humic-like substances (HULIS) are a class of high molecular weight, light-absorbing compounds that are highly related to brown carbon (BrC). In this study, the sources and compositions of HULIS isolated from fine particles collected in Beijing, China during the 2014 Asia-Pacific Economic Cooperation (APEC) summit were characterized based on carbon isotope (13C and 14C) and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses, respectively. HULIS were the main light-absorbing components of water-soluble organic carbon (WSOC), accounting for 80.2 ±â€¯6.1% of the WSOC absorption capacity at 365 nm. The carbon isotope data showed that HULIS had a lower non-fossil contribution (53 ±â€¯4%) and were less enriched with 13C (-24.2 ±â€¯0.6‰) relative to non-HULIS (62 ±â€¯8% and -20.8 ±â€¯0.3‰, respectively). The higher relative intensity fraction of sulfur-containing compounds in HULIS before and after APEC was attributed to higher sulfur dioxide levels emitted from fossil fuel combustion, whereas the higher fraction of nitrogen-containing compounds during APEC may have been due to the relatively greater contribution of non-fossil compounds or the influence of nitrate radical chemistry. The results of investigating the relationships among the sources, elemental compositions, and optical properties of HULIS demonstrated that the light absorption of HULIS appeared to increase with increasing unsaturation degree, but decrease with increasing oxidation level. The unsaturation of HULIS was affected by both sources and aging level.

Mysterious abrupt carbon-14 increase in coral contributed by a comet.

A large and sudden increase in radiocarbon ((14)C) around AD 773 are documented in coral skeletons from the South China Sea. The (14)C increased by ~ 15‰ during winter, and remain elevated for more than 4 months, then increased and dropped down within two months, forming a spike of 45‰ high in late spring, followed by two smaller spikes. The (14)C anomalies coincide with an historic comet collision with the Earth's atmosphere on 17 January AD 773. Comas are known to have percent-levels of nitrogen by weight, and are exposed to cosmic radiation in space. Hence they may be expected to contain highly elevated (14)C/(12)C ratios, as compared to the Earth's atmosphere. The significant input of (14)C by comets may have contributed to the fluctuation of (14)C in the atmosphere throughout the Earth's history, which should be considered carefully to better constrain the cosmic ray fluctuation.

[Composition and seasonal variations of carbon isotopes in aerosols of Lhasa, Tibet].

A total of 30 samples of total suspended particles were collected at an urban site in western of Lhasa city, Tibet from August 2006 to July 2007 for investigating carbonaceous aerosol features. 14C was taken as a reference to quantitatively distinguish the fossil and biogenic-derived origins along with the characteristics of seasonal variations of all carbonaceous materials in Lhasa are discussed. The results showed that the f(c) values in Lhasa ranged from 0.357 to 0.702, with an average of 0.493, which is higher than Beijing and Tokyo, but are far lower than that of remote/rural regions such as Launceston, indicating a major biogenic influence in Lhasa. Values of f(c) displayed clear seasonal variations with higher mean value in winter, a decreasing trend in spring, while relatively lower values in summer and autumn. Higher f(C) values in winter demonstrate that carbonaceous aerosol is mainly dominated by wood burning and incineration of agricultural wastes during the winter. The lower f(c) values in summer and autumn might be caused by increased diesel engines, motor vehicles emissions, which are related to the tourism in Lhasa. delta13C values ranged from -26.40% per hundred to approximately -25.10% per hundred, with an average of -25.8% per hundred, and showed no clear seasonal variation. The relative higher values in summer reflected the increment of fossil carbon emissions. 13C(TC) values are relatively homogeneous at -25.8% per hundred, considering the characteristics of seasonal variations of f(c) values, it can be concluded that carbonaceous aerosol of Lhasa was mainly influenced by a constant mixing of several pollution sources such as motor vehicles and wood burning emissions.

[Spatial and temporal differentiation of mountainous soil organic matter delta 13C in Dinghushan Biosphere Reserve].

Based on the determinations of soil organic matter (SOM) content, SOM delta 14C, and SOM delta13C of the samples collected by thin-layered sampling method, this paper studied the spatial and temporal differentiation of SOM delta13 C in the soil profiles at different altitudes in Dinghushan Biosphere Reserve. The results showed that the vertical differentiation of SOM delta13C at different altitudes was controlled by the development of soil profile, and closely correlated with the composition of SOM and its turnover processes. The fractionation of carbon isotope was happened during both the transformation of vegetation debris into topsoil organic matter (OM) and its regeneration after the topsoil buried, which resulted in a significant increase of SOM delta13C. Relative to plant debris delta13C, the delta13 C increment of topsoil OM was more dependent on its turnover rate. Both the delta13C of plant debris and topsoil OM increased with altitude, indicating the regular variation of vegetations with altitude, which was consensus to the vertical distribution of vegetations in Dinghushan Biosphere Reserve. Soil profiles at different altitudes had similar characteristics in vertical differentiation of SOM delta13C, vertical distribution of SOM content, and increasing apparent age of SOM 14C with soil depth, which were resulted from the successive turnover of SOM during the development of soil profile. The maximum depth of SOM delta13C in soil profile was different in origin and magnitude with the penetration depth of 14C produced by nuclear explosion in the atmosphere, indicating the controlling effects of topography and vegetation on the distribution of SOM carbon isotope with soil depth.

[Quantitative simulation on the vertical distribution of soil organic matters in mountainous soil profiles in the subtropical area, south China].

Quantitative descriptions of soil organic matter (SOM) dynamics, i.e., their distribution, turnover and movement, are essential for the running of the simulation of terrestrial ecosystem organic matter models. In this study, based on utilizing SOM diffusion-translation-decomposition model, two soil profiles were selected in different vegetation zones at Dinghushan Mountain for quantitative studies on SOM dynamics and their controlling factors. SOM were divided into three kinds of compartments: rapid compartment with turnover rate of 0.1-1.yr-1, slow compartment with turnover rate of 0.002-0.02.yr-1, and stable compartment with turnover rate of 0.0001-0.001.yr-1. The numerical results suggested that SOM distribution in soil profile in subtropical mountainous areas of south China obeyed the law of diffusion motion, translation motion and decomposition. The turnover rate of SOM rapid compartment was 0.483.yr-1 in the forest vegetation zone, and was 0.694.yr-1 in the shrub vegetation zone. The turnover rates of SOM slow compartment in the two kinds of vegetation zones were both 0.02.yr-1, and the turnover rates of SOM stable compartment in the two kinds of vegetation zones were both 0.001.yr-1. SOM diffusion rate and translation rate for the forest vegetation zone was 4 cm2.yr-1 and 0.2 mm.yr-1, respectively, and the two rates of the shrub vegetation zone were 1 cm2.yr-1 and 0.5 mm.yr-1, respectively. The obvious discrepancy between numerical values and measuring values for SOM content occurred in the 0-10 cm sections of the profiles, which might be due to the fact that the upper sections were at the interface between lithosphere and atmosphere, and were influenced directly by changes of climatic and environmental factors. The two kinds of values for SOM content were identical below the upper section of the profiles, and it indicated stable pedogenesis environments. Diffusion motion had obvious influences on SOM vertical distribution, and translation motion had clear impacts on SOM distribution only in the upper 0-10 cm section. Comparison analysis suggested that SOM dynamics were controlled mainly by soil profile qualities such as SOM content, clay content, soil fabric, void types and their developments, soil fauna and microorganism activities, etc. With the increasing of primary production of aboveground vegetation, the turnover rate of SOM rapid compartment decreased and SOM content increased, which provided scientific basis for increasing soil carbon sink through anthropogenic effects.