Vacuum Based Gas Sensing Material Characterization System for Precise and Simultaneous Measurement of Optical and Electrical Responses.

Gas sensing performance characterization systems are essential for the research and development of gas sensing materials and devices. Although existing systems are almost completely automatically operated, the accuracies of gas concentration control and of pressure control and the ability to simultaneously detect different sensor signals still require improvement. In this study, a high-precision gas sensing material characterization system is developed based on vacuum technology, with the objective of enabling the precise and simultaneous measurement of electrical responses. Because of the implementation of vacuum technology, the gas concentration control accuracy is improved more than 1600 times, whereas the pressure of the test ambient condition can be precisely adjusted between vacuum and 1.2 bar. The vacuum-assisted gas-exchanging mechanism also enables the sensor response time to be determined more accurately. The system is capable of performing sensitivity, selectivity, and stability tests and can control the ambient relative humidity in a precise manner. More importantly, the levels of performance of three different optical signal measurement set-ups were investigated and compared in terms of detection range, linearity, noise, and response time, based on which of their scopes of application were proposed. Finally, single-period and cyclical tests were performed to examine the ability of the system to detect optical and electrical responses simultaneously, both at a single wavelength and in a spectral region.

[Quantitative estimation source of urban atmospheric CO2 by carbon isotope composition].

To effectively reduce urban carbon emissions and verify the effectiveness of currently project for urban carbon emission reduction, quantitative estimation sources of urban atmospheric CO2 correctly is necessary. Since little fractionation of carbon isotope exists in the transportation from pollution sources to the receptor, the carbon isotope composition can be used for source apportionment. In the present study, a method was established to quantitatively estimate the source of urban atmospheric CO2 by the carbon isotope composition. Both diurnal and height variations of concentrations of CO2 derived from biomass, vehicle exhaust and coal burning were further determined for atmospheric CO2 in Jiading district of Shanghai. Biomass-derived CO2 accounts for the largest portion of atmospheric CO2. The concentrations of CO2 derived from the coal burning are larger in the night-time (00:00, 04:00 and 20:00) than in the daytime (08:00, 12:00 and 16:00), and increase with the increase of height. Those derived from the vehicle exhaust decrease with the height increase. The diurnal and height variations of sources reflect the emission and transport characteristics of atmospheric CO2 in Jiading district of Shanghai.

[Size distributions of organic carbon (OC) and elemental carbon (EC) in Shanghai atmospheric particles].

Size distributions of organic carbon (OC), elemental carbon (EC) and secondary organic carbon (SOC) in atmospheric particles with size range from < 0.49, 0.49-0.95, 0.95-1.50, 1.50-3.00, 3.00-7.20, > 7.20 microm, collected in Jiading District, Shanghai were determined. For estimating size distribution of SOC in these atmospheric particles, a method of determining (OC/EC)(pri) in atmospheric particles with different sizes was discussed and developed, with which SOC was estimated. According to the correlation between OC and EC, main sources of the particles were also estimated roughly. The size distributions of OC and SOC showed a bi-modal with peaks in the particles with size of < 0.49 microm and > 3.0 microm, respectively. EC showed both of a bi-modal and tri-modal. Compared with OC, EC was preferably enriched in particles with size of < 0.49 microm. Mass concentrations of OC and EC in fine particles (< 3.00 microm) accounted for 59.8%-80.0% and 58.1%-82.4% of those in total suspended particles. OC and EC were preferably enriched in fine particles (< 3.00 microm). The concentrations of SOC in the particles with different sizes accounted for 15.7%-79.1% of OC in the particles with corresponding size. Concentrations of SOC in fine aerosols (< 3.00 microm) and coarse aerosols (> 3.00 microm) accounted for 41.4% and 43.5% of corresponding OC. Size distributions of OC, EC and SOC showed time-dependence. The correlation between OC and EC showed that the main contribution to atmospheric particles in Jiading District derived from light petrol vehicles exhaust.