| Since 1950s, automotive exhaust more and more seriously pollutes our environment, air quality has been an issue of major concern in countries world-wide. Although many governments take some measures aimed at improving urban air quality, environment pollution caused by automotive exhaust is also increasing year after year as the sharp increasing of vehicles.The aromatic hydrocarbons pollutants from automotive exhaust -BTEX (benzene, toluene, ethylbenzene and xylene) has been identified as having the effect of causing cancer. In it, benzene's harmfulness to human being is the most serious. It is responsible for leukemia. According to recent study in German and British, more than 80 percent kinds of benzene have relation to vehicle's exhaust. The study shows that a lifetime exposure of 4ppb (13.9μg/m3) gives rise to an excess risk to developing leukemia of 1 per 10,000 inhabitants. Estimates of exposure suggest that over 80 million people are being exposed to levels in excess of World Health Organization (WHO) guidelines. So, it is very important and significant to monitor, real-time and on-line, the BTEX and polycyclic aromatic hydrocarbons from automotive exhaust.In 1994, Ulrich Boesl and other scientists used the technique of REMPI plus TOF-MS and found a lot of toxic pollutants, such as polycyclic aromatic hydrocarbons etc, in the vehicle's exhaust. They called this method as resonant laser mass spectrometry. But this method needs a complex vacuum measurement system. So people pay close attention to BTEX pollutants under the atmospheric pressure. Wessel and his partner proved the possibility that under the atmospheric pressure, resonanceenhanced two-photon ionization (R2PI) principle can selectively identify some molecule. This method has a same ionization theory with TOP except that it needn't use vacuum system. And what's more, the means of measuring the ionized signal are also different. As for the means of measurement, we can use Boxcar Average, Digit Storage Oscilloscope, or Electrometer to measure the ionized signal.In the process of multiphoton ionization, (1+1) ionization (R2PI) is the most effective case. In the case of the most favorable (1+1) ionization, the first photon is absorbed into an excited electronic state, then a second photon is absorbed up to the ionization continuum with adequate efficiency. The experiment apparatus designed by Anhui Institute of Optic and Fine Mechanics Academia Sinica, based upon the technique of resonance enhanced-multiphoton ionization, adopted 248nm KrF excimer laser, measured the ionized signal by electrometer in atmosphere presure. This paper has been finished in the experiment apparatus.This paper has carried out an investigation in BTEX of influencing human being healthy. The main contents include:1. Verify R2PI of benzene, toluene and xylene sample using photocurrent dependence on laser power.2. Work out curve of concentration dependence on laser power of benzene, toluene and xylene sample as criteria of calibration.3. Collect air pollution in urban and measure.4. Deal with data and obtain conclusion.The experiment of collecting sample of air pollution in Hefei city's difference site has been carried out in the last ten-day of twelfth month in 2001. The results of the experiment show that, in different time and different sites, the concentrations of BTEX are different. Its are between 6.72 and 25.64 μ g/m3. The data reflect a regularity: the pollution would be more heavy if the traffic is crowed, on the contrary, it would be light.The next experiment of collecting sample of automotive exhaust ( about 20-3cm near vent ) on Chegongzhuang West Road of Beijing City has been carried out in the last ten-day of first month in 2002. Differences in engine category and fuels used will strongly affect the concentrations of BTEX. The concentrations of BTEX are in the range 14.5μg/m3 and 4318.74 μg/m3. The results show that, at engine cold condition and hot condition, the concentrations of BTEX are different. The con... |
PDF Full Text Request