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Cheng Y.,Tsinghua University | He K.-B.,Tsinghua University | He K.-B.,State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex | He K.-B.,Collaborative Innovation Center for Regional Environmental Quality | And 4 more authors.
Environmental Pollution | Year: 2015

Heavily-polluted PM2.5 (fine particulate matter) episodes frequently impacting Beijing, especially during winter, have become a substantial concern. We found that during winter, the daily variation of PM2.5 in Beijing tracked the pattern of relative humidity (RH). With the increase of PM2.5 (or RH), water-soluble components (especially inorganic ions) became more abundant, and the water-soluble organic carbon to organic carbon ratios increased. The nitrate to sulfate ratios also exhibited dependence on RH, and were higher than those measured about a decade ago, consistent with the increasing trend of nitrogen oxides emissions. Surprisingly, the ratios of water-insoluble organic carbon to elemental carbon showed significant increase at high RH levels, presumably indicating the formation of secondary organic aerosol that is not soluble in water. In addition, humid winters were occasionally identified during 1996-2013 which are expected to be favorable for the formation of air pollution episodes with high PM2.5 concentrations. © 2014 Elsevier Ltd. All rights reserved.

Chen X.,Tsinghua University | Jiang J.,Tsinghua University | Jiang J.,Key Laboratory for Solid Waste Management and Environment Safety | Jiang J.,Collaborative Innovation Center for Regional Environmental Quality | And 2 more authors.
Catalysis Science and Technology | Year: 2015

SiO2 synthesized from photovoltaic waste by a vapor-phase hydrolysis method was applied as a support for a nickel catalyst in a biogas dry reforming process for the first time. The catalytic performance was compared with those of commercial precipitated SiO2 and ordered mesoporous SiO2. Nickel supported on waste-derived SiO2 exhibited high CH4 conversion (92.3%) and high CO2 conversion (95.8%) at 800°C, and there was no deactivation after a 40 h-on-stream test. Catalyst characterization results revealed that the SBET values and pore properties of catalysts affected the catalytic performance. A higher pore volume/SBET ratio led to a smaller crystal metal size and higher metal dispersion, thus the catalyst was less prone to deactivation. This discovery will help improve catalyst design. The use of nickel supported on waste-derived SiO2, which is competitive with commercial and mesoporous catalysts, shows the use of photovoltaic waste as a high value-added product; it can also deliver a cheap and environmentally benign support for catalysts in the biogas dry reforming process. © The Royal Society of Chemistry 2015.

Zheng B.,Tsinghua University | Zhang Q.,Tsinghua University | Zhang Q.,Collaborative Innovation Center for Regional Environmental Quality | Zhang Y.,Tsinghua University | And 10 more authors.
Atmospheric Chemistry and Physics | Year: 2015

Severe regional haze pollution events occurred in eastern and central China in January 2013, which had adverse effects on the environment and public health. Extremely high levels of particulate matter with aerodynamic diameter of 2.5 μm or less (PM2.5) with dominant components of sulfate and nitrate are responsible for the haze pollution. Although heterogeneous chemistry is thought to play an important role in the production of sulfate and nitrate during haze episodes, few studies have comprehensively evaluated the effect of heterogeneous chemistry on haze formation in China by using the 3-D models due to of a lack of treatments for heterogeneous reactions in most climate and chemical transport models. In this work, the WRF-CMAQ model with newly added heterogeneous reactions is applied to East Asia to evaluate the impacts of heterogeneous chemistry and the meteorological anomaly during January 2013 on regional haze formation. As the parameterization of heterogeneous reactions on different types of particles is not well established yet, we arbitrarily selected the uptake coefficients from reactions on dust particles and then conducted several sensitivity runs to find the value that can best match observations. The revised CMAQ with heterogeneous chemistry not only captures the magnitude and temporal variation of sulfate and nitrate, but also reproduces the enhancement of relative contribution of sulfate and nitrate to PM2.5 mass from clean days to polluted haze days. These results indicate the significant role of heterogeneous chemistry in regional haze formation and improve the understanding of the haze formation mechanisms during the January 2013 episode. © Author(s) 2015.

Liu H.,Tsinghua University | Liu H.,Collaborative Innovation Center for Regional Environmental Quality | Wang X.M.,Sun Yat Sen University | Pang J.M.,Sun Yat Sen University | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2013

Improving the air quality in China is a long and arduous task. Although China has made very aggressive plans for air pollutant control, the difficulties in achieving the new air quality goals are still significant. A lot of cities are developing their implementation plan (CIP) for new air quality goals. In this study, a southern city, Guangzhou, has been selected to analyze the feasibility and difficulties of new air quality standard compliance, as well as the CIP evaluation. A comprehensive study of the air quality status in Guangzhou and the surrounding area was conducted using 22 monitoring sites collection data for O3, PM2.5 and PM10. The monthly non-attainment rates for O3 vary from 7 to 25% for May to November. The city average PM2.5 concentration was 53 μgm-3 in Guangzhou in 2010, which needs to be reduced by at least 34% to achieve the target of 35 μgm-3. The PM2.5 high violation months are from November to March. A CIP was developed for Guangzhou, which focused on PM2.5. Based on the CIP, the emission amounts of NOx, PM10, PM2.5 and volatile organic compounds (VOCs) in 2025 would be controlled to 119, 61, 26 and 163 thousand tons, respectively, reduced by 51.9 %, 55.9 %, 61.8% and 41.3 %, respectively, compared to 2010. Analysis of air quality using the model MM5-STEM suggests that the long-term control measures would achieve the PM2.5 and PM10 goals successfully by 2025. The PM2.5 annual average concentration would be reduced to 27 μgm-3 in 2025. However, such PM2.5-based emission control scenarios may enhance the ozone pollution problems. The O 3 non-attainment rate would increase from 7.1% in 2010 to 12.9% in 2025, implying that ozone will likely become a major compliance issue with the new national ambient air quality standards (NAAQS). This suggests that O 3 control must be taken into account while designing PM2.5 control strategies, especially PM2.5 compliance under increased atmospheric oxidation, and for VOCs /NOx reduction ratios need to be further investigated, in order to eventually achieve O3-PM 2.5 co-improvement in this region or other cities. © Author(s) 2013. CC Attribution 3.0 License.

Zheng G.J.,Tsinghua University | Cheng Y.,Tsinghua University | He K.B.,Tsinghua University | He K.B.,State Environmental Protection Key Laboratory of Sources | And 3 more authors.
Atmospheric Measurement Techniques | Year: 2014

The Sunset semi-continuous carbon analyzer (SCCA) is an instrument widely used for carbonaceous aerosol measurement. Despite previous validation work, in this study we identified a new type of SCCA calculation discrepancy caused by the default multipoint baseline correction method. When exceeding a certain threshold carbon load, multipoint correction could cause significant total carbon (TC) underestimation. This calculation discrepancy was characterized for both sucrose and ambient samples, with two protocols based on IMPROVE (Interagency Monitoring of PROtected Visual Environments) (i.e., IMPshort and IMPlong) and one NIOSH (National Institute for Occupational Safety and Health)-like protocol (rtNIOSH). For ambient samples, the IMPshort, IMPlong and rtNIOSH protocol underestimated 22, 36 and 12% of TC, respectively, with the corresponding threshold being ∼ 0, 20 and 25 I1/4gC. For sucrose, however, such discrepancy was observed only with the IMPshort protocol, indicating the need of more refractory SCCA calibration substance. Although the calculation discrepancy could be largely reduced by the single-point baseline correction method, the instrumental blanks of single-point method were higher. The correction method proposed was to use multipoint-corrected data when below the determined threshold, and use single-point results when beyond that threshold. The effectiveness of this correction method was supported by correlation with optical data. © Author(s) 2014. CC Attribution 3.0 License.

Zheng G.J.,Tsinghua University | Duan F.K.,Tsinghua University | Su H.,Max Planck Institute for Chemistry | Ma Y.L.,Tsinghua University | And 12 more authors.
Atmospheric Chemistry and Physics | Year: 2015

Extreme haze episodes repeatedly shrouded Beijing during the winter of 2012-2013, causing major environmental and health problems. To better understand these extreme events, we performed a model-assisted analysis of the hourly observation data of PM2.5 and its major chemical compositions. The synthetic analysis shows that (1) the severe winter haze was driven by stable synoptic meteorological conditions over northeastern China, and not by an abrupt increase in anthropogenic emissions. (2) Secondary species, including organics, sulfate, nitrate, and ammonium, were the major constituents of PM2.5 during this period. (3) Due to the dimming effect of high loading of aerosol particles, gaseous oxidant concentrations decreased significantly, suggesting a reduced production of secondary aerosols through gas-phase reactions. Surprisingly, the observational data reveals an enhanced production rate of secondary aerosols, suggesting an important contribution from other formation pathways, most likely heterogeneous reactions. These reactions appeared to be more efficient in producing secondary inorganics aerosols than organic aerosols resulting in a strongly elevated fraction of inorganics during heavily polluted periods. (4) Moreover, we found that high aerosol concentration was a regional phenomenon. The accumulation process of aerosol particles occurred successively from cities southeast of Beijing. The apparent sharp increase in PM2.5 concentration of up to several hundred 1/4g μ 3 per hour recorded in Beijing represented rapid recovery from an interruption to the continuous pollution accumulation over the region, rather than purely local chemical production. This suggests that regional transport of pollutants played an important role during these severe pollution events. © 2015 Author(s).

Cheng Y.,Tsinghua University | He K.-B.,Tsinghua University | He K.-B.,State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex | He K.-B.,Collaborative Innovation Center for Regional Environmental Quality
Atmospheric Measurement Techniques | Year: 2015

A common approach for measuring the mass of organic carbon (OC) and elemental carbon (EC) in airborne particulate matter involves collection on a quartz fiber filter and subsequent thermal-optical analysis. Although having been widely used in aerosol studies and in PM2.5 (fine particulate matter) chemical speciation monitoring networks in particular, this measurement approach is prone to several types of artifacts, such as the positive sampling artifact caused by the adsorption of gaseous organic compounds onto the quartz filter, the negative sampling artifact due to the evaporation of OC from the collected particles and the analytical artifact in the thermal-optical determination of OC and EC (which is strongly associated with the transformation of OC into char OC and typically results in an underestimation of EC). The presence of these artifacts introduces substantial uncertainties to observational data on OC and EC and consequently limits our ability to evaluate OC and EC estimations in air quality models. In this study, the influence of sampling frequency on the measurement of OC and EC was investigated based on PM2.5 samples collected in Beijing, China. Our results suggest that the negative sampling artifact of a bare quartz filter could be remarkably enhanced due to the uptake of water vapor by the filter medium. We also demonstrate that increasing sampling duration does not necessarily reduce the impact of positive sampling artifact, although it will enhance the analytical artifact. Due to the effect of the analytical artifact, EC concentrations of 48 h averaged samples were about 15 % lower than results from 24 h averaged ones. In addition, it was found that with the increase of sampling duration, EC results exhibited a stronger dependence on the charring correction method and, meanwhile, optical attenuation (ATN) of EC (retrieved from the carbon analyzer) was more significantly biased by the shadowing effect. Results from this study will be useful for the design of China's PM2.5 chemical speciation monitoring network, which can be expected to be inaugurated in the near future. © Author(s) 2015.

Ge H.,Tongji University | Lin Z.,Tongji University | Lin Z.,Collaborative Innovation Center for Regional Environmental Quality | Yao Z.,Tongji University | And 3 more authors.
Aquatic Toxicology | Year: 2014

The use of herbicide mixtures has become a cost-effective strategy against the evolution of herbicide resistance to protect global food production. Much research has focused on investigating either the herbicidal activities or the toxicity effects of herbicides; however, few of them have investigated both factors. This study investigates the balance between herbicidal activity for Selenastrum capricornutum and toxicity effect toward Photobacterium phosphoreum by determining the joint effects of triazine (simetryn, atrazine, prometon and prometryn) and phenylurea (fenuron, monuron, monolinuron and diuron) herbicides. The results showed that among the four triazines, only simetryn exhibited a unique effect (formation of a pi-sigma bond with the D1 microalga protein and an H-bond with the Luc photobacterial protein); and among 16 triazine-phenylurea binary mixtures, only the mixtures containing simetryn resulted in TU1 values (herbicidal activities of mixtures on S. capricornutum) >TU2 values (toxicity effects of mixtures on P. phosphoreum). However, the other 12 mixtures, which did not contain simetryn, showed the opposite result (TU1

Wang D.,Tongji University | Gao Y.,Tongji University | Lin Z.,Tongji University | Lin Z.,Collaborative Innovation Center for Regional Environmental Quality | And 2 more authors.
Aquatic Toxicology | Year: 2014

Metal oxide nanoparticles (NPs) have been used increasingly and are likely to accumulate in natural water bodies, where they encounter and interact with other environmental chemicals. These interactions result in joint effects on biological systems and the environment. However, compared with the intensive research examining the toxicities of individual NPs, the toxicities of NP mixtures remain relatively unexplored. In this work, we studied the joint effects of NPs and their most likely coexisting chemicals in the environment, including NPs with different compositions, humic substances, and surfactants. Our results indicate that the joint effects of NP mixtures were usually simple addition, which is commonly adopted in real risk assessment. However, the joint effects obtained for mixtures that contained ZnO were exclusively associated with antagonism. In addition, the mixtures of NPs and surfactants resulted in complex joint effects, i.e., antagonistic, additive, and synergistic effects were found for the mixtures with ZnO, NiO, and Fe-oxide, respectively. Our study suggests that the assessments of the ecological risk of NPs, particularly ZnO NPs, should consider the impact of their coexisting chemicals in the environment. © 2014 Elsevier B.V.

Wang D.,Tongji University | Lin Z.,Tongji University | Lin Z.,Collaborative Innovation Center for Regional Environmental Quality | Yao Z.,Tongji University | Yu H.,Nanjing University
Chemosphere | Year: 2014

The potential toxicities of nanoparticles (NPs) have been intensively discussed over the past decade. In addition to their single toxicities, NPs can interact with other environmental chemicals and thereby exert joint effects on biological systems and the environment. The present study investigated the combined toxicities of NPs and surfactants, which are among the chemicals that most likely coexist with NPs. Photobacterium phosphoreum was employed as the model organism. The results indicate that surfactants with different ion types can alter the properties of NPs (i.e., particle size and surface charge) in different ways and present complex joint effects on NP toxicities. Mixtures of different NPs and surfactants exhibited antagonistic, synergistic, and additive effects. In particular, the toxicity of ZnO was observed to result from its dissolved Zn2+; thus, the joint effects of the ZnO NPs and surfactants can be explained by the interactions between the Zn ions and the surfactants. Our study suggests that the potential hazards caused by mixtures of NPs and surfactants are different from those caused by single NPs. Because surfactants are extensively used in the field of nanotechnology and are likely to coexist with NPs in natural waters, the ecological risk assessments of NPs should consider the impacts of surfactants. © 2014 Elsevier Ltd.

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