Enhanced electrochemical sensing performance for trace Hg(II) by high activity of Co3+ on Co3O4-NP/N-RGO surface.

Constructing a highly sensitive and selective electrochemical interface is of great significance for the effective detection of Hg2+ in water and biological samples. Herein, Co3O4 nanopolyhedron (NP) anchored on nitrogen-doped reduced graphene oxide (N-RGO) is utilized as the electrode material for the detection of Hg2+ in the range of 0.1 µM-1.0 µM, with high sensitivity (1899.70 µA µM-1 cm-2) and low detection limits (0.03 µM) in natural water. Moreover, the Co3O4-NP/N-RGO modified electrode possesses reasonable anti-interference ability for Hg2+ in the presence of inorganic ions and glucose, which is the basis of its good response to trace Hg2+ in serum. Besides, combined with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, the electron transfer tendency is revealed. Additionally, combined with the electron state density of Co-p, it is speculated that Co3+ is an optimum active site for catalytic reaction. The above results elucidate an electrochemically sensitive interface is constructed to realize the efficient detection of Hg2+, which provides some theoretical guidance for the development of electrochemical sensors.

[Characteristics of Atmospheric BTX near a Main Road in Hefei City].

In order to study levels of BTX near a main road in Hefei in March 2016, benzene, toluene, m-xylene, and o-xylene (BTX) and conventional pollutants (such as NO2 and SO2) in the atmosphere were monitored through a home-made differential optical absorption spectroscopy (DOAS) system. Results showed that average concentrations of benzene, toluene, m-xylene, and o-xylene were 21.7, 63.6, 33.9, and 98.7 µg·m-3, respectively. Compared with other cities both in China and elsewhere, benzene and toluene pollution can be considered to be of medium level, while xylene pollution is serious. Wind direction, T/B ratio, and correlation with CO were also analyzed, together with BTX sources. Result showed that the T/B ratio was 0.8-4.5, with correlation coefficients of benzene, toluene, and CO of 0.55 and 0.34, respectively. These values indicate that benzene and toluene are mainly derived from automotive emissions, also affected by surrounding industrial parks. Xylene is mainly derived from a coating industrial park north of the observation site. It was shown that high night-time concentrations of benzene and toulene could be due to industrial emissions from the industrial parks around the observation site. The ozone formation potential is in the order of o-xylene > m-xylene > toulene > benzene at the observation site. The ozone formation potential of xylene accounted for 85% of total ozone formation potential, indicating that emissions from surrounding industrial parks contribute greatly to ozone formation in the area.

Study of a Laser Wavelength Correction Method Applied to the Measurement of OH Radical with Laser-Induced Fluor.

A method for dye laser wavelength correction applied for the measurement of OH radical with FAGE (Fluorescence Assay by Gas Expansion) is researched in this article. Sufficiently stable concentration of OH radical is produced with thermal dissociation of H2O by using an alumel filament and the fluorescence is excited with 282 nm laser in a low pressure cell. The fluorescence is detected with a photomultiplier and a high speed data acquisition card, while the laser light is monitored by a photodiode, and both signals are handled by a LabVIEW program for further analysis. The data acquisition card is triggered by a positive TTL pulse generated by a digital delay generator, which is triggered by a rising edge of a synchronized output pulse of the dye laser. The LabVIEW program is used to determine the location of the OH excited line according to the fluorescence intensity of OH radical when the frequency of the dye laser is scanned. By scanning dye laser wavelength range in 281.97~282.28 nm, excitation spectrum of OH radical is recorded. In order to optimize system parameters and achieve a high signal-to-noise ratio, the effects of the humidity, oxygen concentration, mass flow and pumping speed on fluorescence intensity and lifetime are studied at Q12 line and less than ±1.9% fluctuations of the fluorescence intensity is obtained. With analysis of the reaction mechanism of the thermal dissociation of H2O, it is concluded that reaction of oxygen and water is a major source of OH radical. Laser output wavelength is scanned in a small range around Q12 line to find out the exact exciting line and then correct the laser's output, which might slightly shift due to the environmental change and leads to reduction of fluorescence intensity. The wavelength correction procedure is implemented many times and the results show that the systematic error of the instrument is less than 0.1 pm. According to the experimental results, this method meets the needs of quantitative accurate measuring tropospheric OH radical by FAGE.

[Quality Optimization Method for Ambient CO(2) Inversion of High Resolution Fourier Transform Infrared Spectrum].

CO(2) retrievals with high quality facilitate resolving the sources and sinks of CO(2) are helpful in predicting the trend in climate change and understanding the global carbon cycle. Based on a nonlinear least squares spectral fitting algorithm, we investigate the optimization method for CO2 products derived from ground-based high resolution Fourier transform infrared spectra. The CO(2) vertical column densities (VCDs) are converted into column-averaged dry air mole fraction XCO(2) by using the fitted O(2) VCDs, and thus the system errors (e. g. pointing errors, ILS errors, zero-level offset) are corrected greatly. The virtual daily variation which is related to air mass factor is corrected with an empirical model. The spectra screening rule proposed in this paper can greatly improve the XCO2 quality. The CO(2) retrievals before and after the optimized method are compared using a typical CO(2) daily time series. After using the optimized method, the fitting error is reduced by 60%, and the two-hours-averaged precision is ~0.071% (equals to ~0.28 ppm), which is perfectly in line with the TCCON (the total carbon column observing network) threshold, i. e., less than 0.1%.

[An Incoherent Broadband Optical Cavity Spectroscopy for Measuring Weak Absorption Cross Section of Sulfur Dioxide].

As a highly sensitive detection technology, incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) have successfully measured a variety of trace gases. According to the principle of cavity enhanced absorption spectroscopy, if the accurate concentration of the target gas, the curve of the mirror reflectance, effective absorption path length, the light intensity of the absorbing gas and non-absorbing gas are known, the absorption cross section of the absorption gas can be measured. The accurate measurements of absorption cross section are necessary for satellite retrievals of atmospheric trace gases and the atmospheric research. This paper describes an incoherent broadband cavity enhanced absorption spectroscopy(IBBCEAS) instrument with 365 nm LED as the light source for measuring absorption cross section of SO2 from 357 to 385 nm which is arising from the spin-forbidden a ³B1--X¹A1 transition. In comparison to the literature absorption cross section of SO2, and correlation coefficient r is 0.997 3. The result shows the potential of the IBBCEAS system for measuring weak absorption cross section.

[The Detection of Atmospheric HONO and NO2 with Fiber Coupling Long-Path Differential Optical Absorption Spectroscopy System].

A new type of fiber coupling Long-Path Differential Optical Absorption Spectroscopy System(LP-DOAS) based on schmidt - cassegrain telescope was introduced in detail in this paper and it was applied to the accurate measurement of the actual atmospheric HONO and NO2. This measuring system simplified the structure of traditional LP-DOAS system, combining with the design of optical fiber coupling.It made full use of the telescope primary mirror's effective area. The effects of the offset, dark current and telescope stray light to the new LP-DOAS system were discussed in this paper; On a clear day, the ratio between telescope stray light and the optical intensities was less than 1%. To verify the accurate of the new LP-DOAS system, the atmospheric NO2 were simultaneously measured with the new LP-DOAS system and traditional LP-DOAS system. The correlation coefficient R2 was up to 0.968. The observation of atmospheric HONO was carried out by using the fiber coupling LP-DOAS in Gucheng, Hebei Province, China, and the detection limit (2σ) of HONO and NO2 was 84.2 and 144.6 ppt , respectively, with 2 490 m path length and the average time resolution of about 30 s. In the whole measurement in Gucheng, the maximum of HONO and NO2 were 3.2 and 37.8 ppb, respectively, and the minimum were both under the detection limits; the ratio of HONO/NO2 at night was calculated.

[Cruise Observation of SO2, NO2 and Benzene with Mobile Portable DOAS in the Industrial Park].

The self-developed portable DOAS instrument based on differential optical absorption spectroscopy(DOAS) and composed of optical fiber spectrograph and multiple-pass cell was introduced. The standard gases of SO2 and NO2 were employed to test the accuracy and stability of the system, and then cruise observation of SO2, NO2 and benzene was carried out using the system in Tongling industrial park. During the entire period, the polluted gases showed high concentrations near the contaminated areas and the maximum concentrations of SO2, NO2 and benzene were 5 023.2, 2 195.2 and 162.5 µg·m-3, respectively. With 12.6 m optical path, the detection limits of SO2, NO2 and benzene were 67.0, 169.9, 30.6 µg·m-3, respectively. The portable DOAS system provides a convenient and effective technique for industrial park about emergency and supervisory monitoring and evaluation of gas leakage and fugitive emissions of gaseous pollutants.

[Sensitivity Study of Aerosol Properties from Observation of Atmospheric Ring Effect].

Ring effect is defined as the phenomenon that the depth of solar Fraunhofer lines in scattered light is less than those observed in direct sunlight. The aerosol could change the light path and the scattering properties in the atmospheric, and influence Raman Scattering Possibility of the photons, and finally affect the filling-up effect. Aerosol parameters (aerosol optical depth, boundary layer height, single scattering albedo, asymmetric factor) could be obtained by observation of the Ring effect in different aerosol condition. The Ring effect is measured by ground-based MAX-DOAS instrument under clear days and the measurement results is compared with McAritim results. The comparison has a good agreement. Radiation transfer model McArtim is used to study the sensitivity of the Ring effect to the aerosol parameters. The study shows that in most conditions, aerosol optical depth (AOD) and boundary layer (bh) height has a great influence to RSP, and in 90 degree elevation angle, RSP has a decrease of 24.6% when AOD varies from 0.1 to 1, and a decrease of 4.4% when bh varies from 1km to 3 km. The study shows RSP is more sensitive to AOD and boundary layer height, which may provide a new method for aerosol profile.

Nocturnal Atmospheric NO3 Radical Monitoring and Analysis in Beijing with Cavity Ring Down System .

The oxidizability of NO3 radical in the nocturnal atmosphere is comparable with that of diurnal OH radical. Given the importance of NO3 radical in the nocturnal chemical process, accurate measurement of its concentration and analysis its nocturnal chemical process have important significance. The article introduces cavity ring-down spectroscopy (CRDS) instrument which is applied to measure atmospheric NO3 radical. Light from a red laser diode (the wavelength is 662 nm and line width is 0.3 nm) is coupled on-axis into an optical cavity formed by a pair of high-reflectivity mirrors (R≥99.998 5%) to achieve an effective absorption path length of approximately 20km. And it researches nocturnal chemical process of NO3 radical in view of the fall and winter heavy traffic areas. The measurement of NO3 radical with cavity ring-down spectroscopy was performed in Beijing from October 29 to November 15, 2014. During the observation, the concentration of NO3 radical is relatively low with the maximum of NO3 radical concentration of 50pptv and the average of its concentration of approximately10 pptv. Combining of NO2, O3 and NO data, the observation results are analyzed. The NO3 production rates ranging from 0.04 to 1.03 pptv·s-1 were calculated throughout the observation, and NO3 lifetime averaged at 68 s. The NO3 loss process in the atmosphere is further analyzed. Combining of related auxiliary data, the influence of different humidity as well as particulate matter concentrates on the atmospheric NO3 removal is researched. When atmospheric RH≥60% and PM2.5 concentration mainly greater than 60 µg·m-3，the correlation coefficient of the logarithmic correlation between NO3 lifetime and NO2 mixing ratio is 0.79，NO3 is mainly removed by the indirect loss process; however, when atmospheric RH≤40% and the concentration of PM2.5 mainly smaller than 60 µg·m-3, because of the observation site is close to national highway and influenced by local pollution source, the direct loss process is main; When atmospheric 40%

[Fast and accurate extraction of ring-down time in cavity ring-down spectroscopy].

Research is conducted to accurate and efficient algorithms for extracting ring-down time (r) in cavity ring-down spectroscopy (CRDS) which is used to measure NO3 radical in the atmosphere. Fast and accurate extraction of ring-down time guarantees more precise and higher speed of measurement. In this research, five kinds of commonly used algorithms are selected to extract ring-down time which respectively are fast Fourier transform (FFT) algorithm, discrete Fourier transform (DFT) algorithm, linear regression of the sum (LRS) algorithm, Levenberg-Marquardt (LM) algorithm and least squares (LS) algorithm. Simulated ring-down signals with various amplitude levels of white noises are fitted by using five kinds of the above-mentioned algorithms, and comparison and analysis is conducted to the fitting results of five kinds of algorithms from four respects: the vulnerability to noises, the accuracy and precision of the fitting, the speed of the fitting and preferable fitting ring-down signal waveform length The research results show that Levenberg-Marquardt algorithm and linear regression of the sum algorithm are able to provide more precise results and prove to have higher noises immunity, and by comparison, the fitting speed of Leven- berg-Marquardt algorithm turns out to be slower. In addition, by analysis of simulated ring-down signals, five to ten times of ring-down time is selected to be the best fitting waveform length because in this case, standard deviation of fitting results of five kinds of algorithms proves to be the minimum. External modulation diode laser and cavity which consists of two high reflectivity mirrors are used to construct a cavity ring-down spectroscopy detection system. According to our experimental conditions, in which the noise level is 0.2%, linear regression of the sum algorithm and Levenberg-Marquardt algorithm are selected to process experimental data. The experimental results show that the accuracy and precision of linear regression of the sum algorithm is considerably close to those of Levenberg-Marquardt algorithm, and on the other hand, the fitting speed of linear regression of the sum algorithm is faster than that of Levenberg-Marquardt algorithm about five times. The experimental results are consistent with the simulation analysis, and it indicates that linear regression of the sum algorithm is the desirable fitting method, as far as our experimental conditions are concerned.

[Measurement of atmospheric NO3 radical with long path differential optical absorption spectroscopy based on red light emitting diodes].

Nitrate radical (NO3) is the most important oxidant in the tropospheric nighttime chemistry. Due to its high reactivity and low atmospheric concentrations, modern red light emitting diodes (LEDs) was proposed as light source in long path differential optical absorption spectroscopy (LP-DOAS) to measure NO3 radical in the atmosphere. The spectral properties of Luxeon LXHL-MD1D LEDs were analyzed in the present paper. The principle of LEDs-DOAS system to measure nitrate radical was studied in this paper. The experimental setup and retrieval method of NO3 radical were discussed in this paper. The retrieved example of NO3 was given and the time series of NO3 concentrations was performed for a week. The results showed that the detection limits of LEDs-DOAS system were 12 ppt for atmospheric NO3 radical when the optical path of LEDs-DOAS system was 2.8 km.

[MAX-DOAS measurements of NO2 column densities and vertical distribution at Ny-Alesund, Arctic during summer].

The multi-axis differential optical absorption spectroscopy (MAX-DOAS), one of the remote sensing techniques for trace gases measurements, is sensitive to the lower atmosphere by eliminating the influence of stratosphere retrieved from zenith-sky spectroscopy. Ground-based MAX-DOAS measurements were carried out to observe NO2 at Ny-Alesund, Arctic from 5th Jul to 1st Aug 2011. The differential slant column densities (DSCDs) of NO2 at four off-axis angles showed typical pattern of tropospheric absorbers. Based on the assumption that NO2 was well mixed in 0-1 km of the troposphere, the mean mixing ratio of NO2 during the measurement period was 1.023E11 molec x cm(-3). The fluctuation of NO2 might be related to the fossil fuel combustions and the photochemical reactions. The vertical distribution of NO2 at 0-3 km showed that NO2 was mainly originated from boundary layer of sea surface.

[Studies on the data processing method in chlorine measurement by differential optical absorption spectroscopy technology].

In this paper, based on Differential Optical Absorption Spectroscopy (DOAS) technique, experimental measurements of chlorine was carried out in the laboratory with a small self-built experimental system. In dealing with the standard cross-section of chlorine, we presented two different methods: triangle filtering and polynomial fitting. Experiments showed that the concentration of chlorine could be accurately retrieved by the latter one. Simulation results showed that the error of retrieval result by fifth-order polynomial fitting was smaller than by other orders and an actual retrieval example shows that the fitting spectrums were nearly coincident with the measured spectrums with a residual delta(peak to peak) below 5 per hundred; The results measured in different sample pools displayed a high linearity of 0.9961 by this method. The main sources of errors during the entire experiment were simply analyzed. According to the experimental result above, it is feasible to detect chlorine using DOAS technology by polynomial fitting.

[Retrieval of NO2 total vertical columns by direct-sun differential optical absorption spectroscopy].

An appropriate reference spectrum is essential for the direct-sun differential optical absorption spectroscopy (DS-DOAS). It depends on the real reference spectrum to retrieve the total vertical column density (VCD). The spectrum detected at the time with minimum sun zenith angle under the relative clear atmospheric condition in the measurement period was conventionally selected as the reference spectrum. Because there is still untracked NO2 absorption structure in the reference spectrum, the VCD retrieved based on the above spectrum is actually relative VCD, which results in larger error. To solve this problem, a new method was investigated. A convolution of extraterrestrial high-precision solar Fraunhofer spectrum and the instrumental function of the spectrometer was computed and chosen as the reference spectrum. The error induced by NO2 absorption structure in the reference spectrum was removed. Then the fitting error of slant column density (SCD) retrieved by this method was analyzed. The correlation between the absolute SCD and the differential slant column density (dSCD) was calculated. The result shows that the error of SCD retrieved by this new method is below 1.6 x 10(16) molecules x cm(-2) on March 7, 2011, while the error generated by the normal method is about 4.25 x 10(16) molecules x cm(-2). The new method decreased more than 62% error. In addition, the results throughout the day were compared to the troposphere VCD from MAX-DOAS and they are in good agreement. It indicates that the new method could effectively reduce the VCD error of the common way.

[Study on the measurement of ambient ammonia in urban area based on open-path DOAS technique].

As a key role in the acid-deposition and the generation of secondary particle matter (PM), measurement of the concentration of atmospheric ammonia in urban area has been attracting the scientists' interests nowadays. After studying the special absorption features of ammonia in short UV wavelength range, detailed concernful issues were put forward in the present paper. The decision of using xenon lamp as the light source was made after the evaluation of measurement of light spectroscopy. Retrieval wavelength band for NH3 was fixed from 204 to 214 nm and optimal method of deducting other interferential gases was also shown. A home-made open-path DOAS (OP-DOAS) system was set up for the measurement of the concentration of atmospheric NH3. The detection limit of such system was calculated with the typical noise level as low as 0.33 microg x m(-3) with the optical path 228 m. Through field experiment in Guangzhou city, such a system can be competent for the online and high time-resolution monitoring of the concentration of atmospheric ammonia. With a significant diurnal variation, the atmospheric ammonia changed from 0.83 to 3.11 microg x m(-3) with the mean value 1.59 microg x m(-3). The representative character of the diurnal variation is that the concentration of NH3 peaks during night while drops to bottom in the daytime. After the error analysis procedure, typical measurement accuracy of such OP-DOAS system was within 10%.

[Comparison of NO2 slant columns between two ground-based MAX-DOAS].

The study of comparison of NO2 SCD between two ground-based multi axis DOAS is introduced. The slant columns of NO2 from JAMASTEC are compared with those of AIOFM during the period from November to 31 December 2009. It says that the more signal to noise ratio is obtained by using the adjusted integral time rather than fixed settings; Two instrument show good accordance in the lower viewing angles, with the correlation coefficient of 0.995, but it becomes bad with higher viewing angles. The low deviation between the two instruments was achieved during the period from 9am to 17pm, the results in the 20 degree direction show best agreement with a deviation of 12%, but in other period the deviation becomes larger. The results in the visible range are better than those in the UV range, the residual in the fit decreases by more than 60%, and the results in the visible range show good agreements with those of AIOFM in the UV range during the whole day.

[Research on the influence of LED temperature shifts on differential optical absorption spectroscopy for measuring NO2].

Influences of LEDs (without etalon structure and center wavelengths are respectively 370 nm (near-UV), 452 nm (blue) and 660 nm(red)) temperature shifts on differential optical absorption spectroscopy(DOAS) for measuring NO2 were studied. NO2 absorption spectra were formed using LED emitting spectra at 10 degrees C. The measured LED spectra at other temperatures were used as reference spectra of DOAS. Thus, NO2 differential optical densities under different LED temperature shifts were acquired and then NO2 differential cross-sections were fitted to the acquired differential optical densities. From fitting results, the linear relations of 0.995, 0.945 and 0.989 correlation between delta of fitting residual and near-UV, blue and red LEDs temperature shifts were found and their slopes are respectively 1.12 x 10(-3), 5.25 x 10(-5) and 7.45 x 10(-4) degrees C(-1). The fitting results show that the influence of temperature shifts of blue LED on DOAS retrieval is negligible and the temperature shifts of near-UV and red LED are impressible to DOAS measurement resulting in degradation of detection sensitivity. The retrieval results of blue LED with and without etalon with similar temperature properties were compared and showed that etalon of LED will greatly increase the influence of temperature shifts of LED on DOAS retrieval.

[Measurement of OH radicals in flame with XeCl excimer laser].

The present paper describes how to measure OH radicals in the flame of alcohol burner flame by using XeCl excimer laser. The instrument consists of a XeCl excimer laser as light source, a multiple-reflection cell with whole path length of light achieving 2 560 meters, and a double pass high resolution echelle spectrometer with resolution 3.3 pm. This paper describes the reason for using the XeCl excimer laser without spectral etaloning and how to get rid of the water in reactor chamber. The results of the experiment get some absorption peak of OH radicals from 308.145 to 308.175 nm. By choosing the appropriate fit area and fitting, the results contrast with the measure data by using Xe lamp as light source.

[BTX monitoring nearby main road traffic in Guangzhou].

In order to study the levels of BTX (benzene, toluene, xylene, etc) nearby the main roads of Guangzhou from November 2010 to December 2010 during the Asian Games, BTX and conventional pollutants such as NO2, O3 in the air were monitored by the DOAS system nearby Huangsha Road, which is in the Liwan District of Guangzhou City. The results showed that, during the entire period, BTX showed a high concentration in the evening and the average concentrations of benzene, toluene, p-xylene, m-xylene and phenol were 15.9 microg x m(-3), 61.3 microg x m(-3), 6.5 microg x m(-3), 16.9 microg x m(-3), 0.88 microg x m(-3), respectively. The average concentrations of benzene and toluene were close to those in other cities, and the ratio of toluene to benzene was in range of 1.2-6.16. Throughout the monitoring period, the correlation coefficient of benzene and toluene was 0.86 and it rose to 0.985 during the high concentration period, indicating that they had the same source in this region. The correlation coefficient between toluene and CO was 0.78, indicating that traffic emissions was the major source of benzene and toluene. Based on the combination of wind speed, wind direction and other meteorological data, it was found that the weather condition was an important factor which affected the BTX concentration, and some possible point sources were suggested nearby the site.

[Monitoring and analysis of vertical profile of atmospheric HONO, NO2 in boundary layer of Beijing].

Based on the scanning differential optical absorption spectroscopy (DOAS) system, field measurement of vertical profiles of HONO and NO2 was performed continuously from Aug. 27, 2007 to Sep. 4, 2007 in Chaoyang District of Beijing, and their vertical profiles were analyzed. Based on the acquired data, the typical vertical variation characteristics of HONO, NO2 and the ratio HONO/NO2 were discussed, and the possible formation sources of HONO were studied. The results indicated that the decrease of HONO with height was faster than the decrease of NO2. The study found good correlation between NO2 and HONO, as well as between the ratio HONO/NO2 and vapor, respectively. Therefore, the authors' conclusion is that HONO was formed by heterogeneous conversion of NO2 on surfaces or near ground and then transported to higher altitudes.