南昌地区黑碳气溶胶的降水清除系数、效率与作用机制

Black carbon aerosols have a great impact on the climate and environment. As an important sinks of black carbon aerosols, precipitation not only affects black carbon pollution situation directly, but also affects its climate and environmental effects indirectly. However，there is a lack of researches on black carbon aerosol scavenging by precipitation, few related scavenging coefficient and efficiency of black carbon aerosols by precipitation has been found, and understanding about scavenging mechanism is also not enough. In this study, observation of the black carbon aerosols in the atmosphere and precipitation will be carried out simultaneously in Nanchang. In order to calculate scavenging coefficient, single Particle Soot Photometer (SP2) will be used to monitor particle size and concentration distributions of black carbon aerosols in the process of precipitation. Then influencing factors of scavenging coefficient will be discussed. Black carbon in precipitation is determined by using DRI-2001 Carbon Analysis Instrument (TOR method, IMPROVE protocol) to calculate its scavenging efficiency. Also influencing factors of scavenging efficiency will be discussed. Basing on Wet Scavening Theory of Aerosol, collision coefficient between raindrops and black carbon particles is calculated by combining obtained scavenging coefficient, black carbon particle size distribution and raindrop size distribution. Collision coefficient between raindrops and black carbon particles calculated can be used to investigate black carbon's precipitation scavenging mechanism. The aims of this project inculde to construct a new method for aerosol wet scavenging research, to master the distributions of black carbon in the atmosphere and precipitation, to offer scavenging coefficient and scavenging efficiency of black carbon aerosol for reference, and to open out scavenging mechanisms. The project will provide significant basic parameters and scientific basis for predicting black carbon aerosol pollution in atmasphere, for assessing the effects on climate and environment of black carbon aerosol correctly, and for calculating the global carbon sink accurately. Meanwhile, the project will improve the theory of aerosol wet scavenging mechanisms.

黑碳气溶胶对气候、环境等具有重要影响，降水作为重要的汇，直接影响其污染状况，间接影响其气候、环境效应。然而目前黑碳气溶胶的降水清除研究少见，清除作用定量化研究鲜见，作用机制尚不明确，因此黑碳气溶胶的降水清除效果和作用机制有待系统深入研究。本研究拟在南昌开展大气和降水中黑碳的同步观测，用SP2仪监测降水过程黑碳气溶胶的粒径和浓度，计算其降水清除系数，讨论控制因素；用TOR法测定降水中黑碳，结合降水时黑碳气溶胶浓度，计算其降水清除效率，明晰控制因素；基于气溶胶湿清除理论，利用所得降水清除系数、黑碳粒子粒径分布和雨滴谱分布，计算雨滴与黑碳的碰撞系数，模拟、探讨其降水清除机制。本项目旨在建立气溶胶湿清除研究新方法，掌握南昌大气、降水中黑碳分布规律，获得黑碳气溶胶的降水清除系数和效率，并揭示清除机制；为黑碳气溶胶污染预测、气候/环境效应评估、碳汇准确定量提供科学依据，丰富和完善气溶胶湿清除机制理论。

研究黑碳气溶胶的降雨清除效率及其影响因素，对黑碳气溶胶的污染预测与控制具有重要意义。2013-2014年对南昌地区降雨过程大气中黑碳气溶胶及雨水中黑碳进行采样监测，分析讨论不同的降雨、季节、环境条件等对黑碳气溶胶降雨清除的影响和作用机制。主要研究结果如下：. (1) 掌握降水过程黑碳气溶胶的分布特征与影响因素：降雨过程黑碳气溶胶浓度为0.16~13.86ug/m3，平均4.3ug/m3，秋冬季高于夏季，且夏季黑碳气溶胶变化幅度大，因夏季降雨频繁，降雨量及降雨强度变化大。黑碳与气溶胶总颗粒无明显相关；黑碳气溶胶浓度还受相对湿度、温度的影响，变化趋势与两者相反。. (2) 掌握降水中黑碳的分布特征与影响因素：雨水中黑碳浓度为0.02~0.96µg/mL，平均0.23µg/mL，黑碳气溶胶被一定程度地冲刷进入雨水中；冬季最高，夏季次之，秋季最低，与黑碳气溶胶的季节分布一致；持续长时间降雨和前期长期未降雨影响雨水中的黑碳；随降雨量增大，雨水中黑碳也增大，但降雨量40mm以上时，增加平缓；电导率与雨水中黑碳成正比，因黑碳表面吸附大量有机物。. (3) 定量黑碳气溶胶的降水清除效率：降雨对黑碳气溶胶的清除效率0.13%~6.68%，降雨对黑碳气溶胶的湿清除不可忽视。. (4) 明晰黑碳气溶胶降水清除的影响与控制因素：黑碳气溶胶的降雨清除效率受降雨量和降雨持续时间的影响与控制，且夏季高于秋冬季，因为夏季降雨量大且雨强变化范围大；持续降雨期间，黑碳气溶胶清除效率逐日降低，雨水中黑碳在第一天降雨中达到最高值，之后逐天递减。 . (5) 揭示黑碳气溶胶的降水清除作用机制：降雨量较小的降雨对大气中黑碳气溶胶的清除不明显，反映降雨对黑碳气溶胶的作用机制主要有拦截和碰撞；温度对黑碳气溶胶的降雨清除效率有影响，反映惯性碰撞和布朗扩散的作用机制。