Amplified Trace Gas Removal in the Troposphere Hofzumahaus, Andreas; Rohrer, Franz; Lu, Keding ...
Science (American Association for the Advancement of Science),
06/2009, Letnik:
324, Številka:
5935
Journal Article
Recenzirano
The degradation of trace gases and pollutants in the troposphere is dominated by their reaction with hydroxyl radicals (OH). The importance of OH rests on its high reactivity, its ubiquitous ...photochemical production in the sunlit atmosphere, and most importantly on its regeneration in the oxidation chain of the trace gases. In the current understanding, the recycling of OH proceeds through HO₂ reacting with NO, thereby forming ozone. A recent field campaign in the Pearl River Delta, China, quantified tropospheric OH and HO₂ concentrations and turnover rates by direct measurements. We report that concentrations of OH were three to five times greater than expected, and we propose the existence of a pathway for the regeneration of OH independent of NO, which amplifies the degradation of pollutants without producing ozone.
To investigate the characteristics and the specific mechanism of continuous haze,comprehensive measurements were conducted from 15 October to 19 November in the Atmospheric Environment Monitoring ...Super-Station in Heshan of Guangdong province.Five haze episodes occurred in October and November 2014 in the Pearl River Delta（PRD）region. The meteorological parameters, gas data, chemical compositions, and optical parameters of the aerosols were obtained. Among these events, the second haze episode,with the highest concentration of PM2.5 of 187.51 μg/m~3, was the most severe. NO~3-was always higher than SO_4~（2-）, which indicated that motor vehicles played an important role in the haze, even though the oxidation rate from SO_2 to SO_4~（2-）was faster than that of NOXto NO_3~-. The difference between the hourly averages of Na＋and K＋during the haze episode and clean days was small, implying that straw combustion and sea salt had no significant effect on the occurrence of haze, and the backward trajectories of the air masses also conformed with this result. The air pollutants were difficult to disperse because of the significant decrease in the planetary boundary layer（PBL） height. Relative humidity played a crucial role in the formation of haze by leading to hygroscopic growth of the diameter of aerosols.
In order to fabricate copper coatings with excellent brightness, a cationic additive was screened by applying the electrochemical method and the theoretical calculation method. The
...adsorption-coordination coupling inhibition
mechanism was proposed to illustrate the influence of the additive methylene blue (MB). The electrochemical behavior of copper electrodeposition influenced by MB was investigated by cyclic voltammetry and chronoamperometry. The copper electrodeposition under the influence of MB is diffusion-controlled, while the nucleation and growth of coating are 3D diffusion-controlled instantaneous nucleation processes. The electroplating process was optimized and bright copper coating can be obtained at wide range of current density according to SEM analysis and AFM analysis. The XRD was used to study the phase structure under the influence of current density and (1 1 1) surface is obtained preferentially with the increase of current density. The mean grain size is within 100 nm according to Scherrer’s formula, illustrating that nanocrystalline copper coating is obtained.
Graphical abstract
A 1 × 2 integrated four-mode power splitter based on multimode interference is proposed and experimentally demonstrated for the first time. A three-dimensional simulation is used to optimize the ...core/cladding refractive index difference and the input waveguide position for the TE 00 , TE 01 , TE 10 , and TE 11 input waveguide modes. Minimum insertion loss (IL) and mode-dependent loss (MDL) of 0.1 and 0.2 dB are predicted, respectively. IL and MDL less than 1 dB can be maintained over a bandwidth of approximately 50 and 25 nm, respectively. The device was fabricated on SiO 2 and experimentally characterized. The variation of the power splitting ratio for each mode is less than 0.4 dB over the full C-band, and the excess losses of the splitter for all four modes exceed the IL of a straight waveguide by less than 1.85 dB.
Background: Epidemiologic evidence for a causative association between black carbon (BC) and health outcomes is limited. Objectives: We estimated associations and exposure—response relationships ...between acute respiratory inflammation in schoolchildren and concentrations of (BC) and participate matter with an aerodynamic diameter of ≤ 2.5 μm (PM2.5) in ambient air before and during the air pollution intervention for the 2008 Beijing Olympics. Methods: We measured exhaled nitric oxide (eNO) as an acute respiratory inflammation biomarker and hourly mean air pollutant concentrations to estimate and PM2.5 exposure. We used 1,581 valid observations of 36 subjects over five visits in 2 years to estimate associations of eNO with BC and PM2.5 according to generalized estimating equations with polynomial distributedlag models, controlling for body mass index, asthma, temperature, and relative humidity. We also assessed the relative importance of and PM2.5 with two-pollutant models. Results: Air pollution concentrations and eNO were clearly lower during the 2008 Olympics. BC and PM2.5 concentrations averaged over 0—24 hr were strongly associated with eNO, which increased by 16.6% 95% confidence interval (CI), 14.1-19.2% and 18.7% (95% CI, 15.0-22.5%) per interquartile range (IQR) increase in BC (4.0 μg/m³) and PM2.5 (149 μg/m³), respectively. In the two-pollutant model, estimated effects of were robust, but associations between PM2.5 and eNO decreased with adjustment for We found that eNO was associated with IQR increases in hourly concentrations up to 10 hr after exposure, consistent with effects primarily in the first hours after exposure. Conclusions: Recent exposure to BC was associated with acute respiratory inflammation in schoolchildren in Beijing. Lower air pollution levels during the 2008 Olympics also were associated with reduced eNO.
Food cooking can be a significant source of atmospheric particulate organic matter. In this study, the chemical composition of particulate organic matter (POM) in PM2.5 emitted from four different ...Chinese cooking styles were examined by gas chromotography−mass spectrometry (GC−MS). The identified species are consistent in the emissions from different Chinese cooking styles and the quantified compounds account for 5∼10% of total POM in PM2.5. The dominant homologue is fatty acids, constituting 73∼85% of the quantified compounds. The pattern of n-alkanes and the presence of β-sitosterol and levoglucosan indicate that vegetables are consumed during Chinese cooking operations. Furthermore, the emissions of different compounds are impacted significantly by the cooking ingredients. The candidates of organic tracers used to describe and distinguish emissions from Chinese cooking in Guangzhou are tetradecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid, levoglucosan, mannosan, galactosan, nonanal, and lactones. During the sampling period, the relative contribution of Chinese cooking to the mass concentration of atmospheric hexadecanoic acid should be less than 1.3% in Guangzhou.
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•Synergistic suppressing mechanism was illustrated to explain the strong suppressing ability of Brilliant Green on copper electrodeposition.•The strong suppressing effect of Brilliant ...Green was confirmed by electrochemical tests.•Copper superconformal electrodeposition was achieved and high FP values (80.52 % to 84.38 %) with low SDT (about 28 μm) was obtained in the optimized condition.
Finding proper additive to achieve copper superconformal electrodeposition is significantly important. Brilliant Green exhibits excellent suppressing ability to the copper electrodeposition according to electrochemical analysis. Meanwhile, 100 mg/L was selected as the optimum value based on the convection-dependent adsorption behavior analysis of Brilliant Green. The interaction among three different additives was also investigated by applying chronopotentiometry as well as Brilliant Green compete to absorb on the cathode surface with SPS. Besides, the introduction of Brilliant Green can improve the transport of cupric ions (Cu2+). The nucleation and growth of copper deposition is 3D diffusion-controlled instantaneous growth process at high overpotential but 3D diffusion-controlled mixing growth process at low overpotential. The synergistic suppressing mechanism was proposed to explain strong suppressing effect of BG on reduction of Cu2+ and the reaction pathways was studied theoretically. Copper interconnect layer with high FP values (80.52 % to 84.38 %) was obtained with low SDT (about 28 μm) after electroplating process was optimized. The surface morphology under the influence of Brilliant Green is compact and uniform and the grain size is reduced by Brilliant Green.
This study reveals aerosol liquid water content (ALWC) in PM2.5 ranged from 2% up to 74%, and the associated secondary inorganic fraction rose from 24% to 55%, while ambient relative humidity (RH) ...increased from 15% to 83% in the atmosphere over Beijing. Unexpectedly, the secondary inorganic fraction in PM2.5 increased with an increase in the ambient RH, which is a meteorological parameter independent of anthropogenic activities, indicating the presence of a feedback mechanism driven by Henry’s law and thermodynamic equilibrium. During haze episodes, simultaneously elevated RH levels and anthropogenic secondary inorganic mass concentrations resulted in an abundant ALWC. The condensed water could act as an efficient medium for multiphase reactions, thereby facilitating the transformation of reactive gaseous pollutants into particles and accelerating the formation of heavy haze. ALWC was well correlated with the mass concentrations of both nitrate and sulfate, indicating both nitrate and sulfate salts play key roles in determining ALWC. Coincident with a significant reduction in SO2 emissions throughout China, nitrates will become a dominant anthropogenic inorganic salt driving ALWC. Thus, the abundance of ALWC and its effects on the aerosol chemistry and climate should be reconsidered.
Secondary organic aerosol (SOA) is an important component of fine particular matter (PM2.5). Most air quality models use an equilibrium partitioning method along with the saturation vapor ...pressure (SVP) of semivolatile organic compounds (SVOCs) to predict SOA formation. However, the models typically assume that the organic particulate matter (OPM) is an ideal mixture and ignore the partitioning of water vapor to OPM. In this study, the Community Multiscale Air Quality model (CMAQ) is updated to investigate the impacts of water vapor partitioning and nonideality of the
organic–water mixture on SOA formation during winter (January) and summer
(July) of 2013 over eastern China. The updated model treats the partitioning of water vapor molecules into OPM and uses the universal functional activity coefficient (UNIFAC) model to estimate the activity coefficients of species in the organic–water mixture. The modified model can generally capture the observed surface organic carbon (OC) with a correlation coefficient R of 0.7 and the surface organic aerosol (OA) with the mean fractional bias (MFB) and mean fractional error (MFE) of −0.28 and 0.54, respectively. SOA concentration shows significant seasonal and spatial variations, with high concentrations in the North China Plain (NCP), central China, and the Sichuan Basin (SCB) regions during winter (up to 25 µg m−3) and in the Yangtze River Delta (YRD) during summer (up to 16 µg m−3). In winter, SOA decreases slightly in the updated model, with a monthly averaged relative change of 10 %–20 % in the highly concentrated areas, mainly due to organic–water interactions. The monthly averaged concentration of SOA increases greatly in summer, by 20 %–50 % at the surface and 30 %–60 % in the whole column. The increase in SOA is mainly due
to the increase in biogenic SOA in inland areas and anthropogenic SOA in
coastal areas. As a result, the averaged aerosol optical depth (AOD) is
increased by up to 10 %, and the cooling effect of aerosol radiative
forcing (ARF) is enhanced by up to 15 % over the YRD in summer. The aerosol
liquid water content associated with OPM (ALWorg) at the surface is relatively high in inland areas in winter and over the ocean in summer, with a monthly averaged concentration of 0.5–3.0 and 5–7 µg m−3, respectively. The hygroscopicity parameter κ of OA based on the κ–Köhler theory is determined using the modeled ALWorg. The correlation of κ with the O:C ratio varies significantly across
different cities and seasons. Analysis of two representative cities, Jinan
(in the NCP) and Nanjing (in the YRD), shows that the impacts of water partitioning
and nonideality of the organic–water mixture on SOA are sensitive to
temperature, relative humidity (RH), and the SVP of SVOCs. The two processes exhibit opposite impacts on SOA in eastern China. Water uptake increases SOA by up to 80 % in the organic phase, while including nonunity activity coefficients decreases SOA by up to 50 %. Our results indicate that both water partitioning into OPM and the activity coefficients of the condensed organics should be considered in simulating SOA formation from gas–particle partitioning, especially in hot and humid environments.
Let \mathcal {H} be a complex, separable Hilbert space and let \mathcal {B}(\mathcal {H}) denote the algebra of all bounded linear operators acting on \mathcal {H}. Given a unitarily-invariant norm ...\Vert \cdot \Vert _u on \mathcal {B}(\mathcal {H}) and two linear operators A and B in \mathcal {B}(\mathcal {H}), we shall say that A and B are polynomially isometric relative to \Vert \cdot \Vert _u if \Vert p(A) \Vert _u = \Vert p(B) \Vert _u for all polynomials p. In this paper, we examine to what extent an operator A being polynomially isometric to a normal operator N implies that A is itself normal. More explicitly, we first show that if \Vert \cdot \Vert _u is any unitarily-invariant norm on \mathbb{M}_n(\mathbb{C}), if A, N \in \mathbb{M}_n(\mathbb{C}) are polynomially isometric and N is normal, then A is normal. We then extend this result to the infinite-dimensional setting by showing that if A, N \in \mathcal {B}(\mathcal {H}) are polynomially isometric relative to the operator norm and N is a normal operator whose spectrum neither disconnects the plane nor has interior, then A is normal, while if the spectrum of N is not of this form, then there always exists a nonnormal operator B such that B and N are polynomially isometric. Finally, we show that if A and N are compact operators with N normal, and if A and N are polynomially isometric with respect to the (c,p)-norm studied by Chan, Li, and Tu, then A is again normal.
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