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A Modified Method to Correct the Measurement Error of TSI3563 Integrating Nephelometer
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摘要: TSI3563型积分式浊度计是一种性能出色的气溶胶散射系数观测仪器，然而由于仪器设计所固有的限制，TSI3563型浊度计观测结果包含有角度截断和非朗伯体光源两项系统性误差，会使观测结果较真值偏小10%左右。因此，需要对TSI3563型浊度计的观测结果进行校正才能得到较为精确的散射系数观测值。该研究利用2009年华北平原HaChi气溶胶外场观测数据测试了现有校正方法，结果显示，传统的校正方法在我国华北平原这样的高气溶胶污染地区并不适用。为此，提出一种改进的校正方法，利用同时观测的PM1和PM10数据，在校正方案中加入超微米粒子体积比这一参量，对于不同体积比采用不同的校正函数。利用实际观测数据检验后发现，改进方法的校正效果相对于传统方法有很大改善。
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关键词:
- 气溶胶散射系数;
- TSI3563三波段积分浊度计;
- 角度截断和非理想光源误差
Abstract: TSI3563 integrating nephelometer is designed for high-quality in-situ aerosol scattering measurement, which is widely used all over the world. However, the scattering coefficient measured by TSI3563 nephelometer contain two systematic errors: The truncation error (i.e., the geometrical blockage of near-forward/backward-scattered light) and the non-Lambertian error (i.e., the slightly non-cosine weighted intensity distribution of illumination light provided by the opal glass diffusor). These errors need to be corrected since they can typically cause a bias of about 10% in the measured scattering coefficient. Based on the aerosol properties measured in North China Plain during Hachi (Haze in China) Project, the correction factor is calculated with a traditional method and the Mie model (taken as reference) which requires aerosol number size distribution and refractive index as input. The traditional correction method is widely used all over the world since it requires only data from nephelometer itself. However, results show the traditional method cannot provide a good estimation of the correction factor. Due to the high concentration of submicron aerosol in PM10, aerosol number size distributions measured in North China Plain are different from those assumed in the traditional method. The traditional correction method is therefore inadequate for high-aerosol pollution region like North China Plain. It is found that the correction factor is sensitive on the volume fraction of supermicron aerosol in PM10. Higher volume fractions would lead to higher correction factors. A modified correction method is proposed. The volume fraction of supermicron aerosol which can be obtained from PM1 and PM10 measurement is used in the new method. For different volume fractions, different parameters are chosen for the calculation of correction factors. Testing with aerosol properties measured in North China Plain, the modified method provided a good estimation of the correction factors. 80% of correction factors calculated with the modified method are with a bias less than 1% and 100% are with a bias less than 3%. Compared with the traditional method, a distinct improvement is found in correction results. It suggests that to estimate the correction factor for TSI3563 nephelometer measurement, the Mie model should be the first choice if a real-time measurement of aerosol number size distribution is available. Otherwise, the modified method proposed should be used if a real-time PM1 and PM10 measurement is available. Without those parallel measurements, the traditional method can be the last choice to estimate the correction factor. -
图 1 基于HaChi观测数据计算得到的3个波长下TSI3563型浊度计校正因子和Ångströmm指数
Fig. 1 Relationship between the correction factor and Ångström exponent calculated based on HaChi measurements
图 2 基于随机生成的气溶胶谱分布计算得到的550 nm下浊度计校正因子和Ångström指数的关系
Fig. 2 Relationship between the correction factor and Ångström exponent at 550 nm wavelength calculated from randomly generated aerosol number size distributions
图 3 基于观测的气溶胶谱分布计算的不同方法校正结果与参考值差异的频率分布
Fig. 3 Frequency distributions of the bias between correction factor calculated with different methods and reference values
图 4 基于观测的气溶胶谱分布计算的不同方法校正结果与参考值差异的累积概率分布
Fig. 4 Cumulative distribution function of the bias between correction factor culculated with different methods and reference values
表 1 Anderson和Ogren提出的校正公式中所用参数[5]
Table 1 Parameters used in the correction function of Anderson and Ogren's method (from Reference [5])
参数 450 nm 550 nm 700 nm PM10切割 PM1切割 PM10切割 PM1切割 PM10切割 PM1切割 a 1.365 1.165 1.337 1.152 1.297 1.120 b -0.156 -0.046 -0.138 -0.044 -0.113 -0.035 Cave 1.290 1.094 1.290 1.073 1.260 1.049 
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表 2 不同参数设置下550 nm校正因子C550的夏季平均值及与参考情形的相对偏差
Table 2 Relative differences between C550 calculated under different parameter assumptions and the reference value
情形 mr, non mi, non mr, BC mi, BC 混合状态 C550 相对偏差/% 参考情形 1.53 10-7 1.75 0.55 部分内混合、部分外混合 1.1174 0 情形1 1.50 10-7 1.75 0.55 部分内混合、部分外混合 1.1208 0.30 情形2 1.55 10-7 1.75 0.55 部分内混合、部分外混合 1.1150 -0.21 情形3 1.53 10-7 1.50 0.55 部分内混合、部分外混合 1.1190 0.14 情形4 1.53 10-7 2.00 0.55 部分内混合、部分外混合 1.1157 -0.15 情形5 1.53 10-7 1.75 0.44 部分内混合、部分外混合 1.1169 -0.04 情形6 1.53 10-7 1.75 0.66 部分内混合、部分外混合 1.1177 0.03 情形7 1.53 10-7 1.75 0.55 均匀内混合 1.1178 0.04 情形8 1.53 10-7 1.75 0.55 外混合 1.1171 -0.03
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表 3 改进的校正方法中校正函数对于不同fvsm范围的参数选择
Table 3 Parameters for different fvsm range used in the improved method
fvsm 450 nm 550 nm 700 nm a b c a b c a b c [0, 0.1) 0.0073 -0.0630 1.1738 0.0069 -0.0577 1.1617 0.0078 -0.0536 1.1450 [0.1, 0.2) 0.0095 -0.0648 1.1794 0.0105 -0.0609 1.1670 0.0162 -0.0665 1.1559 [0.2, 0.3) 0.0136 -0.0727 1.1930 0.0174 -0.0741 1.1836 0.0302 -0.0959 1.1833 [0.3, 0.4) 0.0206 -0.0878 1.2127 0.0265 -0.0898 1.2020 0.0419 -0.1088 1.1959 [0.4, 0.5) 0.0275 -0.0990 1.2334 0.0310 -0.0865 1.2120 0.0442 -0.0868 1.1904 [0.5, 0.6) 0.0310 -0.0994 1.2554 0.0329 -0.0751 1.2273 0.0445 -0.0604 1.1967 [0.6, 0.7) 0.0443 -0.1155 1.2951 0.0443 -0.0765 1.2602 0.0531 -0.0442 1.2220
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