Summer O3 pollution cycle characteristics and VOCs sources in a central city of Beijing-Tianjin-Hebei area, China.

One of the major pollutants influencing urban air quality in China is O3. O3 is the second most important pollutant affecting air quality in Shijiazhuang, which is the third largest city in the Beijing-Tianjin-Hebei area and the provincial capital of Hebei province. To fully understand the characteristics of O3 and volatile organic compounds (VOCs), which are O3 precursors, and the role of VOCs to ozone formation, we measured the hourly concentrations of O3 and 85 VOCs in Shijiazhuang continuously from January to November 2020, and the concentration characteristics of both together with the chemical reactivity and sources of VOCs were analyzed from a seasonal perspective. The O3 concentration in Shijiazhuang showed a phenomenon of high summer and low winter, and the VOCs showed a phenomenon of high winter and low spring. In the summer when the O3 exceedance rate is the highest, the time-domain variation characteristics of O3 were analyzed by wavelet analysis model, and the main periods controlling the O3 concentration variation in Shijiazhuang in summer 2020 were 52 days, 32 days, 19 days and 12 days. The maximum incremental reactivity (MIR) and propylene equivalence method indicated ethene, propylene and 1-pentene were common substances in the top five species of each season. The T/B, Iso-p/N-p, Iso-p/E, N-p/E, and positive matrix factorization (PMF) model showed that industrial source (18.62%-22.03%) and vehicle emission (13.20%-17.69%) were the major VOCs sources in Shijiazhuang. Therefore, to control the O3 concentration in Shijiazhuang, it is necessary to decrease alkenes emissions as well as VOCs from industrial source and vehicle emission.

[Fault Analysis and Treatment of GE Brivo MR355 1.5 T Magnetic Resonance Gradient System and Cooling System].

The GE Brivo MR355 1.5 T magnetic resonance system is difficult to maintain due to its complex structure and principle. Clinical engineers should be familiar with the basic structure and operation principle of the equipment. After the failure of the equipment occurs, they should first check the error information, combine the fault phenomenon and maintenance manual, clear their thoughts and carefully analyze the possible causes of the failure, and adopt the method of step-by-step elimination, principle analysis and exchange of the same principle. After replacing the chip tantalum capacitor and sumitomo cold head of the same model, the equipment resumed normal operation. As a clinical engineer, regular equipment inspection and preventive maintenance should be done for large equipment, which is conducive to reducing the equipment failure rate.