Concentrations of benzo[a]pyrene (B[a]P) in ambient air from different areas in Lanzhou city in northwest of China, and its metabolite 1-hydroxypyrene (1-OHP) in the urine of resident children and adults were determined by using gas chromatography/mass spectrometry and high performance liquid chromatography. Results showed that the atmospheric environmental concentration of B[a]P varied significantly from one part of the city to another with levels of 150 ng/m(3) in the industrial area of Xigu and 73.8 ng/m(3) in the agricultural area of Yuzhong. The geometric mean urinary 1-OHP concentration was 0.42 µmol/mol-creatinine, with a range of means between 0.067 and 2.05 for the various population sub-groups. The non-occupationally exposed populations' age, gender and area of residence were the major factors that influenced urinary 1-OHP levels. The health risks of B[a]P for adults and children in Xigu and for children in Yuzhong exceeded the acceptable level (1 × 10(-4)) of the US Environmental Protection Agency.
In order to promote the idling noise quality of a single-cylinder gasoline engine, this paper addresses sound source identification and noise control research. The noise was identified by the application of subjective evaluation, acoustic spectrum and sound intensity analysis. It was found that the noise was caused by the anomalous dynamic performance of the timing system under idling conditions. Furthermore, sound and vibration characteristics of timing system were improved by design methodology research of key components. A multi-body dynamic model was established to characterize dynamic characteristics of the timing system under idling conditions. The key factor of producing noise was that the fluctuation of contact force between the chain and guide and transverse displacement of the chain were much higher than those of the allowable design limit. For the lowest design alternation and manufacturing costs, the work analyzed six timing system improvement schemes obtained by cross combination of tensioner blade line and guide strip radian parameters. After that, the optimal design scheme which could improve dynamic performance parameters of the timing system was derived. The design scheme was conducted with a acoustic test of engine to derive the following results. The noise level of a single-cylinder engine under idling conditions decreased by 3 dB(A). The abnormal noise of the original engine was eliminated under subjective evaluation. The sound quality under other working conditions had no apparent deterioration. Research shows that guide and tensioner blade line optimization design could improve dynamic performance of the timing chain system to eliminate abnormal noise, thereby significantly improving the acoustic characteristic of a single-cylinder engine.
Diesel particulate filter is impedance to elastic wave. In order to promote the anechoic performance of diesel particulate filter in designing process, the acoustic characteristics of which were analyzed on the basis of acoustic four-terminal method. The transfer matrix of simplified diesel particulate filter structure was derived to construct the acoustic simulation model, and a two-load experiment of impedance tube was implemented to calibrate the simulation model. On this basis, the correlation between diesel particulate filter structural parameters and acoustic characteristics was investigated. The results show that the transmission loss is sensitive to porosity, gap, layer thickness, and aspect ratio of porthole for a certain diameter diesel particulate filter. Furthermore, two types of diesel particulate filter structures which were octagonal inlet matches square outlet and asymmetric square channels possess superior noise elimination effect compared with the traditional square channel types. At a certain frequency range, the peak noise was reduced by 2-3 dB. The study could provide guidance to the designing of diesel particulate filter anechoic performance.
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