ABSTRACT
Volatile organic compounds (VOCs) in ambient air can participate in photochemical reactions, which lead to the generation of secondary pollutants such as ozone and aerosol. So real-time and accurate monitoring of atmospheric VOCs plays an important role in the study of the causes of air pollution. On the basis of proton transfer reaction mass spectrometry (PTR-MS) research, a novel dipolar proton transfer reaction mass spectrometer (DP-PTR-MS) for real-time and on-line monitoring atmospheric VOCs was developed. Compared with the conventional PTR-MS with one kind of reagent ion H3O+, DP-PTR-MS had three kinds of reagent ions H3O+, OH-, (CH)2COH+, which could be switched according to the actual detection need. So DP-PTR-MS can improve the qualitative ability and expand the detection range effectively. The reagent ion H3O+can be used for detecting VOCs whose proton affinities are greater than that of H2O. The reagent ion OH-can be used to identify VOCs cooperating with the reagent ion H3O+,and can also be used for detecting some inorganic substances such as CO2. The reagent ion (CH3)2COH+can be used for accurately detecting NH3under interference elimination circumstances. The limit of detection (LOD) and sensitivity of DP-PTR-MS were measured by using six kinds of standard gases. The results showed that the LOD for detecting toluene was 7×10-12(V/V) and the sensitivity for detecting ammonia has reached 126 cps/10-9 (V/V). The ambient air in Hefei city was on-line and real-time monitored for continuous 78 hours with DP-PTR-MS. The results showed that the newly developed DP-PTR-MS could be used for long-term and real-time monitoring atmospheric VOCs with the concentration of 10-12(V/V) level. DP-PTR-MS is an important tool for the study of the causes of atmospheric pollution and the monitoring of trace VOCs emissions.
ABSTRACT
<p><b>OBJECTIVES</b>The purpose of this study is to define and clarify the causes of differences in physique between urban students and rural students in China.</p><p><b>METHODS</b>Subjects are 2,524 students (male, 838; female, 1686) who entered K University in Shanghai in September, 2001. The data used in this study is based upon K university's Yearly Health Check Record and Students' Family Condition Record. Correlation analysis, analysis of variance (ANOVA) and analysis of covariance (ANCOVA) were applied to analyze the relationships between physique and gross family income, family income per capita, latitude, air temperature, precipitation or altitude.</p><p><b>RESULTS</b>Urban students' height and weight are significantly greater than rural students' in both males and females. Both male students and female students are significantly taller and heavier in accordance with per capita increases in students' family income. The height and weight of male and female students whose parents are peasant farmers are least. With regard to the relationship between physique and urban-rural factors, the F value decreases clearly when family income per capita is taken as a covariate, while the F values slightly decrease also when factors of latitude etc. are taken as covariates. The main cause of differing family income is occupational difference between urban areas and rural ones.</p><p><b>CONCLUSION</b>Students born in urban areas are taller and heavier than those born in rural areas. The main cause of these differences is family income per capita. The main cause of variations in family income is the income difference in occupations.</p>