| Volatile organic compounds (VOCs) are kinds of compounds that the boiling point are between 50-260℃and are easy to volatile when saturated vapor pressure is more than 133.32Pa at the room temperature. VOCs not only have significant toxic effects on human body, but also are the precursor materials of urban and regional atmospheric chemical reactions which have a major impact on atmospheric oxidation potential. Therefore, the studys of characteristics and variation of VOCs in ambient air pollution are of great significance and application values.In this paper, dates of VOCs were monitored by on-line GC in Springs Square from July 2010 to June 2011 in Jinan city, and the monitoring data of O3, NOX and meteorological conditions are obtained at the same time. Basic dates were analysised by means of computer data processing softwares according to the recent domestic and international references, and the main conclusions are as follows:(1) The majority VOCs in ambient air in Jinan are alkanes, aromatics and olefins, which average concentrations are 37.06μg/m3,9.67μg/m3 and 14.82μg/m3 respectively. Ethane, isobutane, butane, cyclopentane, isopentane, toluene, ethylbenzene, m/p-xylene,1,2,4-trimethylbenzene, ethylene, propylene and isoprene are the main VOCs in ambient air in Jinan. The concentration range of aromatics is big, the alkane is relatively small, and the concentration of olefin is the smallest of all yet the most concentrated.(2) The daily average concentrations of TVOCs in ambient air of Jinan are significantly high in summer and fall, and are lower in spring and winter relatively. Alkanes are the main component of VOCs in ambient air in Jinan; the ranges of average percentage of mass concentration of olefins and aromatics are big, in which the trend of olefm concentration percentage range is autumn> summer> spring> winter, and the aromatic has the opposite trend to it. VOCs all have clear bimodal in sunny days, yet there are no obvious bimodal in rainy days and the concentration are significantly high. The intermediatevalue are closer to the mean value of hour concentration of TVOCs in the day than in the night.(3) Alkanes are mainly from the use of LPG fuels, olefins are mainly from vehicle emissions, industrial volatilization and burning of organic materials have greate contribution to aromatics apart from motor vehicle exhaust in Jinan according to the analysis of correlations among concentrations of the typical VOCs.(4) Meteorological conditions such as wind speed, hours of daylight and atmospheric stability have greate impact on pollutant concentrations in ambient air, VOCs and O3, for instance. The concentrations of pollutants have significant downward trends when wind speed is more than 2 m/s; the overall levels concentration of VOCs are low when there is a longer hours of sunshine, yet concentration of 8-hour average ozone has the opposite vary trend; because of the pollutants are easy to spread, the concentration shows a growth trend when there is stable atmosphere.(5) The daily average concentration of O3 is significantly high in summer and fall, and is relatively lower in spring and winter in ambient air in Jinan. And the daily average concentrations of O3 have similar trend in different seasons, which shows a single peak variation. The maximum 8-hour average concentration of O3 appears during the period from 10:00 to 17:00, the over standard days are more than 60 in one year that account for 24.3%of the total statistical number of days, and the over standard rate in summer and fall is 48.9%. The over standard days of 1-hour average concentration of O3 are concentrated in summer and fall, and merely appears in spring and winter.(6) VOCs, NOx and other pollutants are the precursors of photochemical reaction. The maximum concentration of VOCs and NOx appear in the morning of heavy traffic times, and O3 concentration increases rapidly along with the enhancement of solar radiation which reachs a high concentration at noon, yet 4-5 hours later than NO when it reaches the peak.(7) The corelation among concentrations of pollutants and pollution indicators in the most active period of photochemical reaction (10:00～17:00) in ambint air in Jinan City are as follows:concentration of O3 has negative correlation with concentration of NO and TVOCs/NOx values, has positive correlation with concentration of NO2 and TVOCs/NOx values, and has little correlation with concentration of TVOCs. The VOCs/NOx values are at low level, so the generation of O3 is not limited to the concentration of NOx, but is significantly increased with the increase of VOCs, Therefore, control the generation and emissions of VOCs can be effective in preventing the occurrence of photochemical smog in Jinan City. |
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