| The Biogenic Volatile Organic Compounds (BVOCs) had certain influence on atmospheric environment, air quality, human health, isoprene and a-pinene had high emissions among them. Yunnan was located in low latitude and high altitude, with characteristics of various floristics, high forest coverage, low air humidity, agrometeorological drought, long sunshine time and high ultraviolet radiation. The emission characteristics of major natural source should be determined, to provide not only scientific data for forecasting global climate change and atmospheric environmental quality, but also scientific basis for plant species selection and atmospheric environment improvement of of Yunnan. Based on this, the composition, seasonal variation, monthly variation, diurnal variation, hourly variation of BVOCs emissions from Sabina Chinensis, Cedar and eucalyptus were investigated by collecting volatiles gas samples with headspace sampling method and analyzing them by Electronic Nose (zNose4200) instantly from November,2010to October,2011. The factors of plant itself (site, leaf age) and environmental factors (weather, temperature, relative humidity) which effected emission of BVOCs from plants were also studied. The results showed that:(1) The analytical method for the rapid and instant determination of BVOCs by Electronic Nose technology (GC/SAW) was established. The method could reflect the true concentration of BVOCs without sample pretreatment and have no effect on samples, which had the advantages of better reproducibility, higher sensitivity and accuracy.(2) There were larger emissions of BVOCs from Sabina Chinensis, Cedar and eucalyptus, a-pinene and isoprene were main components. The emissions of BVOCs varied with the plant species, Eucalyptus>Sabina Chinensis>cedar. The average emissions of a-pinene were less than isoprene any time.(3) The emission laws of the main BVOCs from three typical plants were wave mode curve, which had significant monthly variation (April>May), diurnal variation (April was larger than May) and hourly variation. The concentration curves of Sabina Chinensis and eucalyptus presented "two peaks two vales" in April and "three peaks two vales" in May; Cedar concentration presented "two peaks one vale" in April and in May; the highest peak of them appeared at noon.(4)The variation of main BVOCs concentration from eucalyptus:①Seasonal variation: Summer>Spring>Autumn> Winter, a-pinene annual average relative content was5.63%; average relative content of isoprene annual was24.58%.②Monthly variation:the emissions of a-pinene and isoprene were higher in July, September and October, and lower in February, November and December.③Diurnal variation:the emission dynamic curves of a-pinene and isoprene showed wavy, the concentration curves of a-pinene and isoprene presented "three peaks two vales" and "one peak one vale" in Spring and in Summer respectively; the concentration curves of a-pinene presented "one peak two vales" and "three peaks three vales" in Autumn and in Winter respectively; the concentration curves of isoprene presented "two peaks three vales" and "two peaks two vales" in Autumn and in Winter respectively.④Hourly variation:they always presented peaks in10:00,13:00～14:00and in19:00～21:00; they always presented vales in11:00,12:00and15:00～18:00; the highest peak of them appeared at noon; The emissions in the night were less than in the daytime.(5) Plant species, the plant factors (site, leaf age), weather, temperature, humidity, etc. can affect plant release BVOCs. The variation of BVOCs relative emissions:leaves>stem; young leaves>old leaves; cloudy>rain>sunny for a-pinene, sunny>cloudy>rain for isoprene; the relative emissions of BVOCs were affected by the temperature, humidity, which had a certain correlation, the Pearson Correlation coefficients (r) were in the range of0.019～1.000. Isoprene release was more dependent on temperature changes; the release of a-pinene was more dependent on the humidity changes.(6) Comparing with correlation between temperature and eucalyptus BVOCs relative emissions in nighttime and during the day, the influence of the temperature during the day was larger than the night. The correlations between isoprene relative emissions and temperature showed that the influence of the day was more than the correlation between a-pinene relative emissions and temperature in the daytime, it was opposite at night. Comparing with eucalyptus BVOCs relative emissions and humidity in the day and night, the relative emissions of a-pinene has better correlation at night than during the day, the influence of isoprene displayed difference. Comparing with the correlation between humidity and a-pinene, isoprene relative emission, the former was better all the time.(7) The annual average release rate of a-pinene was4.21μgC/g·h; the annual average release rate of isoprene was266.97μgC/g·h. The overall emissions (Ten thousand tons each year) of a-pinene and isoprene from eucalyptus in Yunnan were1.89and119.63, respectively. |
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