Xiaowen Shu

Aerosol optical properties observed by combined Raman‐elastic backscatter lidar in winter 2009 in Pearl River Delta, south China

We present combined Raman and elastic backscatter lidar observations in Zhongshan, PRD (Pearl River Delta), China, during two periods in 2009: one haze period and one moderate pollution period. During the haze period, high Aerosol Optical Depth (AOD) (0.86 and 1.20 at 355 nm) and medium Angstrom exponents (1.23 and 1.35 at 355 nm/532 nm) were observed. In the moderate pollution period, the corresponding parameters were comparatively lower with values of 0.83 and 0.74 at 355 nm for AOD and 1.108 and 0.98 at 355 nm/532 nm for Angstrom exponent. The mean lidar ratios in the two periods were 64 ± 10 sr and 56 ± 9 sr, respectively, at 355 nm. The Angstrom exponent was calculated for the extinction from the wavelength pair 355 nm/532 nm, with high values of around 1.35 for the haze event. The particle size distribution and single-scattering albedo derived from Sun photometer measurements indicate the presence of rather small particles. The 3 day back trajectories from a Hybrid Single-Particle Lagrangian Integrated Trajectory model in the haze period indicate that the air masses in the lower layer were advected from the southeast coast of China, where incomplete combustion of carbonaceous fuels and straw burning are frequently found in Shanghai during the heating period in winter. In the moderate pollution period, the air mass passed through western China, indicating a combination of some pollution from South Asia in case of strong convection, local aerosol aging, and smoke from adjacent fire burning spots in the PRD region.

Gas leakage monitoring with scanned-wavelength direct absorption spectroscopy

A natural gas leakage detector based on scanned-wavelength direct absorption spectroscopy is described. The sensor employs a multi-channel scanned-wavelength direct absorption strategy. It has the potential to simultaneously monitor methane and hydrogen sulfide in open path environment. Traditionally, scanned wavelength direct absorption spectroscopy is the technique choice for natural gas leakage applications because of its simplicity, accuracy, and stability. We perform the gas sensor using direct-absorption wavelength scans with isolated features at 1-kHz repetition rate and the center wavelength is stabilized at the center of the 2 \nu 3 band R(3) line of methane (1.65 \mu m) and the (\nu 1 +\nu 2 +\nu 3) combination band of hydrogen sulfide (1.57 \mu m), respectively. The influence of light intensity fluctuations can be eliminated by using scanned-wavelength direct absorption spectroscopy. Because of the fast wavelength scanning, the sensor has a response time of less than 0.1 s. The sensor can be configured to sense leakages in path-integrated concentrations of, for example, 100-ppm·m hydrogen sulfide and 10-ppm·m methane.

The measurement of the H2S in the pre-desulfurization of natural gas in the Shengli oil field with the TDL

Hydrogen Sulfide, with the character of erosion and strong toxicity, is a kind of associated gas of nature gas. How to measure and monitor the hydrogen sulfide concentration becomes an important issue to be solved in nature gas transfer-process. Online measurement for the hydrogen sulfide concentration before the desulphurization remains very difficult in Bonan gas gathering station of SINOPEC Shengli Oil Field (SOF).TDL(Tunable Diode Laser) can relative easily select the absorption line of the detecting gas without the interference from other gas thus make the rapid and accurate hydrogen sulfide measurement a possible. In this paper, a hydrogen sulfide measurement system is designed and then be carried out in Bonan gas gathering station of (SOF) .The implemented experiments showed the system effectively solved some problems such as overfall, temperature and pressure. After comparing the hydrogen sulfide online detection sensor of the TDLAS industry with the long hydrogen sulfide detection tube, the linear fitted relationship with the correlation coefficient of 99.96% between them was attained. In order to meet the requests of industrial field anti-explosion, the open-path optical coupling technology was performed in china for the first time. All the results demonstrate that the system will be put into use and enjoy a high application in the near future.

Vertical Distribution Characteristics of PM 2.5 Observed by a Mobile Vehicle Lidar in Tianjin, China in 2016

We present mobile vehicle lidar observations in Tianjin, China during the spring, summer, and winter of 2016. Mobile observations were carried out along the city border road of Tianjin to obtain the vertical distribution characteristics of PM2.5. Hygroscopic growth was not considered since relative humidity was less than 60% during the observation experiments. PM2.5 profile was obtained with the linear regression equation between the particle extinction coefficient and PM2.5 mass concentration. In spring, the vertical distribution of PM2.5 exhibited a hierarchical structure. In addition to a layer of particles that gathered near the ground, a portion of particles floated at 0.6–2.5-km height. In summer and winter, the fine particles basically gathered below 1 km near the ground. In spring and summer, the concentration of fine particles in the south was higher than that in the north because of the influence of south wind. In winter, the distribution of fine particles was opposite to that measured during spring and summer. High concentrations of PM2.5 were observed in the rural areas of North Tianjin with a maximum of 350 μg m–3 on 13 December 2016. It is shown that industrial and ship emissions in spring and summer and coal combustion in winter were the major sources of fine particles that polluted Tianjin. The results provide insights into the mechanisms of haze formation and the effects of meteorological conditions during haze–fog pollution episodes in the Tianjin area.

Description of a system based on the DFB laser for natural gas leakage in the long optical-path of the tunnel

The leakage of methane and sulfureted hydrogen in the tunnel may threaten the environment, safety and lead to damage and casualties. In this paper, a system based on the distribution feedback laser is introduced to detect the leakage natural gas in the tunnel. The system can be used in the tunnel with the length over 2km. In the system, two approaches, namely the direct absorption and wavelength modulation is both adopted to acquire the concentration of methane and sulfureted hydrogen. The results show that the remote sensing can reach up to two kilometers with the detectability of methane 2ppm and sulfureted hydrogen 20ppm respectively. This system is carried out in the Puguang Gas filed for the first time and satisfactory results are obtained, making up the gap in such field as detecting natural gas in domestic market.

Exhaust gas monitoring based on absorption spectroscopy in the process industry

This non-invasive gas monitor for exhaust gas monitoring must has high reliability and requires little maintenance. Monitor for in-situ measurements using tunable diode laser absorption spectroscopy (TDLAS) in the near infrared, can meet these requirements. TDLAS has evolved over the past decade from a laboratory especially to an accepted, robust and reliable technology for trace gas sensing. With the features of tunability and narrow linewidth of the distributed feedback (DFB) diode laser and by precisely tuning the laser output wavelength to a single isolated absorption line of the gas, TDLAS technique can be utilized to measure gas concentration with high sensitivity. Typical applications for monitoring of H2S, NH3, HC1 and HF are described here together by wavelength modulation spectroscopy with second-harmonic(WMS-2F) detection. This paper will illustrate the problems related to on-line applications, in particular, the overfall effects, automatic light intensity correction, temperature correction, which impacted on absorption coefficient and give details of how effect of automatic correction is necessary. The system mainly includes optics and electronics, optical system mainly composed of fiber, fiber coupler and beam expander, the electron part has been placed in safe analysis room not together with the optical part. Laser merely passes through one-meter-long pipes by the fiber coupling technology, so the system itself has anti-explosion. The results of the system are also presented in the end, the systems response time is only 0.5s, and can be achieved below 1×10−5 the detection limit at the volume fraction, it can entirely replace the traditional methods of detection exhaust gas in the process industry.