[A method for resolving spectra shift in the urban air quality monitoring system (DOAS)].

In the urban air quality monitoring system, there is spectra shift which is caused by environment factors on the optical part (temperature and optic fiber position), or by the self-change of Xe-lamp. Relative spectra shift will occur if the shift of lamp-spectrum and air-spectrum is inconsistent which has direct influences on the accuracy of the measurement results. So the match of wavelength between lamp-spectrum and air-spectrum should be considered when we retrieve pollutants concentration measurement of trace gas in the atmosphere through DOAS method. Based on the study of the unique structures for Xe-lamp emitting spectrum, a method for the calibration of two signal spectra using Xe-lamp emitting peak and least square fitting is given. The results show that, the impact of spectrum shift can be reduced by this method for retrieving results.

[Study on the measurement of the atmospheric extinction of fog and rain by forward-scattering near infrared spectroscopy].

In the visible and near IR, absorption is negligible so that the atmospheric extinction can be derived by atmospheric scattering which is mainly contributed by fog droplet, rain droplet, another types of droplet and small articles. The forward-scattering visibility meter (FVM) works by illuminating with near IR light a small sample volume of about 100 mL of air and measuring the intensity scattered in the angular range of 30 to 36 degrees. The scattered intensity is proportional to the extinction coefficient regardless of the article size distribution and after wavelength calibration. The ratio of scattered signal to extinction coefficient of fog and haze can be achieved by comparative test of FVM outputs and manual observations. Nevertheless, as a result of the application of the measurement during rain with the ratio of fog and haze, an unacceptable error is raised. To obtain an accuracy extinction measurement during rain, an appropriated ratio of scattered signal to extinction coefficient of rain would be found. The calculation for different size distributions of fog and rain with Mie theory has been made in this paper. And a comparison of extinction measurements made with two FVMs and manual observations during fog and rain has been made. The result shows that during rain the FVM extinction coefficient is from 20% to 60% greater than that of manual observations. This result can be used to define correction factors so that the FVM using forward-scattering near IR spectroscopy not only can be used to estimate extinction during fog and haze as well as during rain.

[Study on the method for rapid determination of oil concentration in water].

The rapid determination of oil concentration in water was investigated with three dimensional fluorescence spectra and parallel factor analysis (PARAFAC), and the influence of dissolved organic matter on the measurement of oil concentration was analyzed mainly. No. 0 diesel oil and humic acid was used for measuring sample in the experiment, the fast separation of No. 0 diesel oil fluorescence spectra from the overlapped spectrum of humic acid was studied through changing humic acid concentration, the contents of No. 0 diesel oil was obtained under different humic acid simulation conditions, the maximum average error was 1.67%, and the relative standard deviation was less than 1.29%. The results showed the possibility of oil concentration fast determination with a variation of dissolved organic matter in water based on three dimensional fluorescence spectra technique and PARAFAC.

[Observational study of black carbon aerosol during straw-burning period].

Black carbon aerosol (BC) has been measured at three sites in Hefei City during May and June, 2007. Analyzing these real-time BC data, the concentration characters and the sources of black carbon aerosol can be found. The average concentrations of BC in normal period and straw-burning period are 4.85 microg/m3 and 8.38 microg/m3, respectively. The significant difference shows that the straw-burning is one of the main sources. The correlation coefficients between daily average concentration of BC and PM10 is 0.74, while the values of BC/PM10 in normal period and straw-burning period are 4.7% and 7.9%, respectively. Through comparing to the BC concentration during straw-burning period in 2004, the results indicated that pollution of BC has reduced after straw-burning was forbidden by the government.

[Retrieval of monocyclic aromatic hydrocarbons with differential optical absorption spectroscopy].

Differential optical absorption spectroscopy (DOAS) technique has been used to measure trace gases in the atmosphere by their strongly structured absorption of radiation in the UV and visible spectral range, e. g. SO2, NO2, O3 etc. However, unlike the absorption spectra of SO2 and NO2, the analysis of aromatic compounds is difficult and strongly suffers from the cross interference of other absorbers (Herzberg bands of oxygen, ozone and sulfur dioxide), especially with relatively low concentrations of aromatic compounds in the atmosphere. In the present paper, the DOAS evaluation of aromatic compounds was performed by nonlinear least square fit with two interpolated oxygen optical density spectra at different path lengths and reference spectra of ozone at different temperature and SO2 cross section to correct the interference from absorbers of O2, O3 and SO2. The measurement of toluene, benzene, (m, p, o) xylene and phenol with a DOAS system showed that DOAS method is suitable for monocyclic aromatic compounds monitoring in the atmosphere.

[An analysis of quenching characteristics of DOM in water by laser induced fluorescence].

In the experiment an excitation resource at 355 nm from a third harmonic Q-switched Nd:YAG laser was used, and the commercial humic acid of different concentrations was used as the research samples. The fluorescence spectrum of dissolved organic matter (DOM) in combination with laser-induced fluorescence (LIF) measurements was measured in the laboratory, and the characteristics of fluorescence quenching of DOM were analyzed. The results show that the intensity of water Raman scattering and DOM fluorescence was reduced gradually and increased linearly respectively with raising the concentration of humic acid. The water Raman scattering signal was absorbed almost completely by the ground state molecules of DOM at 40 mg x L(-1), and the fluorescence intensity of DOM reached a maximum at 16 mg x L(-1) and decreased slowly with further increasing the concentration of humic acid. Consequently, we can achieve better monitoring of DOM in water through analyzing the characteristics of fluorescence quenching at different concentrations of humic acid.

[The fluorescence emission of water at upconversion of frequency by laser induced fluorescence].

The fluorescence spectra of several types of water samples in combination with laser-induced fluorescence (LIF) measurements using 532 nm wavelength excitation source were measured in the laboratory, and the fluorescence matters such as dissolved organic matter (DOM), chlorophyll a (Chl a) and carotenoids were pointed out with spectral fluorescent signature (SFS) technique. It is considered that the peak at 455 nm in the spectrum is contributed by carotenoid (PPC). Finally, the dynamic model of PPC's fluorescence emission is showed.

[The influence of temperature change on determined concentrations of dissolved organic matter in water].

The influence of temperature change on the determined concentrations of dissolved organic matter (DOM) in water was investigated by laser induced fluorescence (LIF) technique in laboratory. The temperature was altered within the range of 20 to 75 degrees C, and the intensity of DOM fluorescence and water Raman scattering were found to decrease with rising temperature. A linear fit of the normalized fluorescence intensity versus temperature yielded a mean value of the temperature coefficient of -5.24 x 10(-4) x degrees C(-1), and a mean value of the temperature coefficient of -3.42 x 10(-3)(mg x L(-1)) x degrees C(-1) was obtained according to the relationship between normalized fluorescence intensity and concentration of DOM. The temperature change will cause relative changes of up to 8.45% in DOM concentration within the range of 20 to 75 degrees C if we assume that the normalized fluorescence intensity remains the same.

[Passive FTIR remote sensing of gaseous pollutant in heated plume].

The principle and techniques of passive remote sensing of gaseous pollutant in heated plume was illustrated and discussed in this paper. The algorithm of radiance spectra and transmittance spectra in measured region was proposed, and the method of retrieving gas concentrations with NLLS fitting algorithm was also proposed. The remote senseing of actual gaseous pollutant of smokestack was done, and the quantitative analysis of SO2 and CO2 was completed.

[Study on UV-visible DOAS system based on photodiode array (PDA)].

A long-path differential optical absorption spectroscopy (DOAS) system is introduced. A photodiode array is employed as the detector to replace the complicated SD detector which consists of a PMT and a slotted disk. The properties of the detector and the spectrometer unit such as offset, dark current, noise, linearity, resolution, and wavelength range were measured. This system was also tested to measure SO2 and NO2 in the atmosphere. The detection limits of this system for SO2, and NO2 over a 713 m light path were determined.