Fang Cao

Enhanced reductive dechlorination of DDT in an anaerobic system of dissimilatory iron-reducing bacteria and iron oxide

The transformation of DDT was studied in an anaerobic system of dissimilatory iron-reducing bacteria (Shewanella decolorationis S12) and iron oxide (alpha-FeOOH). The results showed that S. decolorationis could reduce DDT into DDD, and DDT transformation rate was accelerated by the presence of alpha-FeOOH. DDD was observed as the primary transformation product, which was demonstrated to be transformed in the abiotic system of Fe(2+)+alpha-FeOOH and the system of DIRB+alpha-FeOOH. The intermediates of DDMS and DBP were detected after 9 months, likely suggesting that reductive dechlorination was the main dechlorination pathway of DDT in the iron-reducing system. The enhanced reductive dechlorination of DDT was mainly due to biogenic Fe(II) sorbed on the surface of alpha-FeOOH, which can serve as a mediator for the transformation of DDT. This study demonstrated the important role of DIRB and iron oxide on DDT and DDD transformation under anaerobic iron-reducing environments.

Is it time to tackle PM2.5 air pollutions in China from biomass-burning emissions?

An increase in haze days has been observed in China over the past two decades due to the rapid industrialization, urbanization and energy consumptions. To address this server issue, Chinese central government has recently released the Action Plan on Prevention and Control of Air Pollution, which mainly focuses on regulation of indusial and transport-related emissions with major energy consumption from fossil fuels. This comprehensive and toughest plan is definitely a major step in the right direction aiming at beautiful and environmental-friendly China; however, based on recent source apportionment results, we suggest that strengthening regulation emissions from biomass-burning sources in both urban and rural areas is needed to meet a rigorous reduction target. Here, household biofuel and open biomass burning are highlighted, as impacts of these emissions can cause local and regional pollution.

Effect of Aeromonas hydrophila on reductive dechlorination of DDTs by zero-valent iron.

This study presents a reductive transformation method that combines zerovalent iron (ZVI) and Aeromonas hydrophila HS01 with iron oxide reduction property to degrade DDT (1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) under anoxic conditions. The results suggest that HS01 has weak capability in terms of reducing DDT to DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) and nearly failed to reduce DDD or its transformed intermediates. The coexistence of ZVI and HS01 results in a slight enhancement of DDT degradation compared with the ZVI system alone. The reduction of intermediates by ZVI, however, can be obviously accelerated in the presence of HS01, and the addition of anthraquinone-2,6-disulfonic disodium salt (AQDS) can accelerate the transformation rates further, especially for intermediate reduction. The analysis of the amount and electrochemical properties of Fe(III)/Fe(II) indicates that the presence of HS01 with or without AQDS is beneficial to the reduction of Fe(III) to Fe(II), resulting in the removal of passivating ferric precipitates on the ZVI surface. A mechanism and pathway that clarify the roles of ZVI, HS01, and AQDS in the ZVI + HS01 + AQDS system for DDT transformation are proposed. The quick removal of surface ferric precipitates is thought to be the reason for the enhancement of the transformation of DDT and its intermediates.

Inorganic markers, carbonaceous components and stable carbon isotope from biomass burning aerosols in Northeast China

To better characterize the chemical compositions and sources of fine particulate matter (i.e. PM2.5) in Sanjiang Plain, Northeast China, total carbon (TC), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and inorganic ions as well as stable carbon isotopic composition (δ13C) were measured in this study. Intensively open biomass burning episodes are identified from late September to early October by satellite fire and aerosol optical depth maps. During the biomass-burning episode, concentrations of PM2.5, OC, EC, and WSOC are increased by a factor of 4-12 compared to those during the non-biomass-burning period. Non-sea-salt potassium is strongly correlated with PM2.5, OC, EC and WSOC, demonstrating an important contribution from biomass-burning emissions. The enrichment in both the non-sea-salt potassium and chlorine is significantly larger than other inorganic species, suggesting that biomass-burning aerosols in Sanjiang Plain are mostly fresh and less aged. In addition, the WSOC-to-OC ratio is lower than that reported in biomass-burning aerosols in tropical regions, further supporting that biomass-burning aerosols in Sanjiang Plain are mostly primary and secondary organic aerosols may be not significant. A lower average δ13C value (-26.2‰) is observed during the biomass-burning period, indicating a dominant contribution from combustion of C3 plants in the studied region.

Stable carbon isotopic compositions of low‐molecular‐weight dicarboxylic acids, oxocarboxylic acids, α‐dicarbonyls, and fatty acids: Implications for atmospheric processing of organic aerosols

Stable carbon isotopic compositions (δ13C) were measured for 23 individual organic species including 9 dicarboxylic acids, 7 oxocarboxylic acids, 1 tricarboxylic acid, 2 α-dicarbonyls, and 4 fatty acids in the aerosols from Gosan background site in East Asia. δ13C values of particle phase glyoxal and methylglyoxal are significantly larger than those previously reported for isoprene and other precursors. The values are consistently less negative in oxalic acid (C2, average −14.1‰), glyoxylic acid (−13.8‰), pyruvic acid (−19.4‰), glyoxal (−13.5‰), and methylglyoxal (−18.6‰) compared to other organic species (e.g., palmitic acid, −26.3‰), which can be explained by the kinetic isotope effects during atmospheric oxidation of pre-aged precursors (e.g., isoprene) and the subsequent gas-particle partitioning after the evaporation of clouds or wet aerosols. The δ13C values of C2 is positively correlated with C2 to organic carbon ratio, indicating that photochemical production of C2 is more pronounced than its degradation during long-range atmospheric transport. The isotopic results also suggest that aqueous phase oxidation of glyoxal and methylglyoxal is a major formation process of oxalic acid via the intermediates such as glyoxylic acid and pyruvic acid. This study provides evidence that organic aerosols are intensively photochemically aged in the western North Pacific rim.

Microgram-level radiocarbon determination of carbonaceous particles in firn and ice samples: pretreatment and OC/EC separation

Carbonaceous particles that comprise organic carbon (OC) and elemental carbon (EC) are of increasing interest in climate research because of their influence on the radiation balance of the Earth. The radiocarbon determination of particulate OC and EC extracted from ice cores provides a powerful tool to reconstruct the long-term natural and anthropogenic emissions of carbonaceous particles. However, this 14C-based source apportionment method has not been applied for the firn section, which is the uppermost part of Alpine glaciers with a typical thickness of up to 50 m. In contrast to glacier ice, firn samples are more easily contaminated through drilling and handling operations. In this study, an alternative decontamination method for firn samples consisting of chiselling off the outer parts instead of rinsing them was developed and verified. The obtained procedural blank of 2.8 ± 0.8 μg C for OC is a factor of 2 higher compared to the rinsing method used for ice, but still relatively low compared to the typical OC concentration in firn samples from Alpine glaciers. The EC blank of 0.3 ± 0.1 μg C is similar for both methods. For separation of OC and EC for subsequent 14C analysis, a thermal-optical method instead of the purely thermal method was applied for the first time to firn and ice samples, resulting in a reduced uncertainty of both the mass and 14C determination. OC and EC concentrations as well as their corresponding fraction of modern for firn and ice samples from Fiescherhorn and Jungfraujoch agree well with published results, validating the new method.

High Contribution of Nonfossil Sources to Submicrometer Organic Aerosols in Beijing, China

Source apportionment of organic carbon (OC) and elemental carbon (EC) from PM1 (particulate matter with a diameter equal to or smaller than 1 μm) in Beijing, China was carried out using radiocarbon (14C) measurement. Despite a dominant fossil-fuel contribution to EC due to large emissions from traffic and coal combustion, nonfossil sources are dominant contributors of OC in Beijing throughout the year except during the winter. Primary emission was the most important contributor to fossil-fuel derived OC for all seasons. A clear seasonal trend was found for biomass-burning contribution to OC with the highest in autumn and spring, followed by winter and summer. 14C results were also integrated with those from positive matrix factorization (PMF) of organic aerosols from aerosol mass spectrometer (AMS) measurements during winter and spring. The results suggest that the fossil-derived primary OC was dominated by coal combustion emissions whereas secondary OC was mostly from fossil-fuel emissions. Taken together with previous 14C studies in Asia, Europe and USA, a ubiquity and dominance of nonfossil contribution to OC aerosols is identified not only in rural/background/remote regions but also in urban regions, which may be explained by cooking contributions, regional transportation or local emissions of seasonal-dependent biomass burning emission. In addition, biogenic and biomass burning derived SOA may be further enhanced by unresolved atmospheric processes.

High Time- and Size-Resolved Measurements of PM and Chemical Composition from Coal Combustion: Implications for the EC Formation Process

Inefficient coal combustion is a significant source of elemental carbon (EC) air pollution in China, but there is a limited understanding of ECs formation processes. In this study, high time-resolved particle number size distributions (PNSDs) and size-resolved chemical compositions were obtained from the combustion of four bituminous coals burned in a quartz tube furnace at 500 and 800 °C. Based on the distinct characteristics of PNSD, the flaming stage was divided into the first-flaming stage (with a PNSD peak at 0.3-0.4 μm) and the second-flaming stage (with a PNSD peak at 0.1-0.15 μm). For the size-segregated EC and OC measurements, more soot-EC was observed in particles larger than 0.3 μm, whereas the smaller ones possessed more char-EC. The results indicated that gas-phase and direct-conversion EC generation mechanisms dominate different burning stages. The analysis of 16 parent PAHs showed more high-molecular-weight PAHs in the second-flaming stage particles, which supports the idea of different formation processes for char-EC and soot-EC. For all four coals, the PNSD and chemical compositions shared a similar trend, confirming that the different formation processes of EC in different flaming stages were common. This study provides novel information concerning EC formation.

Nitrogen isotope fractionation during gas-particle conversion of NO x toNO 3 − in the atmosphere – implications for isotope-based NO x source apportionment

Atmospheric fine-particle (PM2.5) pollution is frequently associated with the formation of particulate nitrate (pNO−3 ), the end product of the oxidation of NOx gases (NO+NO2) in the upper troposphere. The application of stable nitrogen (N) (and oxygen) isotope analyses of pNO−3 to constrain NOx source partitioning in the atmosphere requires knowledge of the isotope fractionation during the reactions leading to nitrate formation. Here we determined the δ15N values of fresh pNO−3 (δ N–pNO3 ) in PM2.5 at a rural site in northern China, where atmospheric pNO−3 can be attributed exclusively to biomass burning. The observed δ15N– pNO−3 (12.17± 1.55 ‰; n= 8) was much higher than the N isotopic source signature of NOx from biomass burning (1.04± 4.13 ‰). The large difference between δN–pNO3 and δN–NOx (1(δ15N)) can be reconciled by the net N isotope effect (εN) associated with the gas–particle conversion from NOx to NO−3 . For the biomass burning site, a mean εN(≈1(δ 15N)) of 10.99± 0.74 ‰ was assessed through a newly developed computational quantum chemistry (CQC) module. εN depends on the relative importance of the two dominant N isotope exchange reactions involved (NO2 reaction with OH versus hydrolysis of dinitrogen pentoxide (N2O5) with H2O) and varies between regions and on a diurnal basis. A second, slightly higher CQC-based mean value for εN (15.33± 4.90 ‰) was estimated for an urban site with intense traffic in eastern China and integrated in a Bayesian isotope mixing model to make isotope-based source apportionment estimates for NOx at this site. Based on the δ15N values (10.93± 3.32 ‰; n= 43) of ambient pNO−3 determined for the urban site, and considering the location-specific estimate for εN, our results reveal that the relative contribution of coal combustion and road traffic to urban NOx is 32 %± 11 % and 68 %± 11 %, respectively. This finding agrees well with a regional bottom-up emission inventory of NOx . Moreover, the variation pattern of OH contribution to ambient pNO−3 formation calculated by the Published by Copernicus Publications on behalf of the European Geosciences Union. 11648 Y. Chang et al.: Nitrogen isotope fractionation during NOx to pNO−3 formation CQC module is consistent with that simulated by the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), further confirming the robustness of our estimates. Our investigations also show that, without the consideration of the N isotope effect during pNO−3 formation, the observed δN–pNO3 at the study site would erroneously imply that NOx is derived almost entirely from coal combustion. Similarly, reanalysis of reported δN–NO3 data throughout China and its neighboring areas suggests that NOx emissions from coal combustion may be substantively overestimated (by > 30 %) when the N isotope fractionation during atmospheric pNO−3 formation is neglected.