草地异戊二烯排放通量影响因子的研究

A Study of the Affecting Factors of Isoprene Emission at Grassland

20 0 2年夏季对中国内蒙古草原挥发性有机物的排放通量进行的首次测量结果表明 ,其主要成分异戊二烯的排放有明显的日变化和季节变化。采样箱对太阳辐射有非常明显的衰减作用 ,其衰减率为 1 7%～ 35 %。为准确估算异戊二烯的排放通量 ,建立其排放模式是非常必要的。基于可见光辐射传输与守恒的观点 ,在观测数据的基础上建立了异戊二烯排放通量的经验模式。结果表明 ,对日变化、季节变化和日总量的模拟值与测量值比较一致。在使用箱方法时 ,应该考虑箱内外辐射、温湿度、水汽含量之差引起的排放通量的差别 ,特别是箱内外辐射之差所引起排放通量的差别。同时也说明 ,可见光辐射是影响异戊二烯排放的最主要因子。利用异戊二烯排放通量的日总量与 1 1 :0 0通量之比和可见光辐射日总量与 1 1 :0 0时累计值之比的定量关系 ,可以由某日 1 1 :0 0的排放通量来推算该日的日总量 ,其平均相对偏差小于 1 4%。

The emission fluxes of volatile organic compounds (VOC) in the Inner Mongolia during the summer of 2002 were measured firstly. The results show that emission flux of isoprene, the main component of VOC exhibited obvious diurnal and seasonal variation. The chamber had an evident attenuation to the solar radiation, its attenuation rate was between 17%～35%. It is necessary to build a model to accurately estimate isoprene emission flux. On the basis of transmission and conservation of solar visible radiation and the analysis on observation data, an empirical model of isoprene emission was built up. The results showed that modeled values for diurnal, seasonal and daily total emission fluxes were basically consistent with that measured. When using the static chamber method, the difference of isoprene emission flux caused by the differences of solar visible radiation, temperature, humidity and water vapor content between the inside and outside of the chamber should be considered, especially for the difference of solar visible radiation. The results also showed that solar visible radiation was the most important factor to affect isoprene emission. The quantitative relation between ratios of daily sum to 11:00 accumulated valve of isoprene emission flux to that of solar visible radiation can be used to estimate daily sum of isoprene flux from measured emission flux at 11:00, and its mean relative basis was less than 14%.