Correcting aethalometer black carbon data for measurement artifacts by using inter-comparison methodology based on two different light attenuation increasing rates
Correcting aethalometer black carbon data for measurement artifacts by using inter-comparison methodology based on two different light attenuation increasing rates
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DOI：
10.5194/amtd-8-2851-2015
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
Y.-H. Cheng;L.-S. Yang
中科院分区：
文献类型：
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作者：
Y.-H. Cheng;L.-S. Yang
抽象的。在使用基于滤波器的光学技术获得的炭黑（BC）测量中，伪影是主要问题。最近，它已成为可能，以纠正这些文物在一定程度上通过使用数值方法。然而，在现场条件下，所有校正方案都有其优点和缺点。在这项研究中，提出了一种新的校正模型，可用于确定伪影的影响BC测量，该模型是基于两个不同的光衰减（ATN）增加率。使用两个蒸发仪以6和2 L min−1的气溶胶采样流速平行测量ATN值。在不存在采样伪影的情况下，两台蒸发仪测得的ATN值之比应等于这两台蒸发仪的采样流速（或气溶胶沉积速率）之比。在实际应用中，由于气溶胶负荷效应随气溶胶沉降速率的变化而变化，两台气溶胶浓度计测得的ATN值之比与两台气溶胶浓度计的采样流速之比并不相同。如果可以找到真实的ATN值，则可以通过使用真实的ATN变化率来校正BC测量结果的伪影。因此，确定真实的ATN值是本研究的主要目的。该校正算法可用于从不同采样流量下获得的ATN值获得真实的ATN值，并可从真实的ATN变化率确定实际的BC质量浓度。在BC校正之前，在夏季和冬季，以6 L min−1的采样流速测量的BC浓度分别比以2 L min−1测量的浓度小约13%和9%。在使用真实ATN值进行BC校正后，6 L min−1的校正BC可以精确等于2 L min−1的校正BC。现场试验结果表明，该模型可以准确地校正载荷对BC测量的影响。另外，在不使用任何光散射系数的情况下，可以克服由在未加载滤波器处的光散射引起的增强的光ATN的问题。因此，校正算法可以应用到一个新设计的仪器，以确定实际的实时BC浓度，通过使用两个采样点不同的气溶胶沉积速率。此外，还提出了一个简单的经验修正方案，用于对已有的蒸散仪BC数据进行后处理修正。虽然这种简单的校正方案取决于气溶胶类型，但当BC的主要来源和天气条件与本研究中的相似时，它可以用于校正BC数据。此外，可以使用两种具有适当流量控制的现有酒精计来创建适合不同环境的校正方案。
Abstract. In black carbon (BC) measurements obtained using the filter-based optical technique, artifacts are a major problem. Recently, it has become possible to correct these artifacts to a certain extent by using numerical methods. Nevertheless, all correction schemes have their advantages and disadvantages under field conditions. In this study, a new correction model that can be used for determining artifact effects on BC measurements was proposed; the model is based on two different light attenuation (ATN) increasing rates. Two aethalometers were used to measure ATN values in parallel at aerosol sampling flow rates of 6 and 2 L min−1. In the absence of sampling artifacts, the ratio of ATN values measured by the two aethalometers should be equal to the ratio of the sampling flow rates (or aerosol deposition rates) of these two aethalometers. In practice, the ratio of ATN values measured by the two aethalometers was not the same as the ratio of the sampling flow rates of the aethalometers because the aerosol loading effects varied with the aerosol deposition rate. If the true ATN value can be found, then BC measurements can be corrected for artifacts by using the true ATN change rate. Therefore, determining the true ATN value was the primary objective of this study. The proposed correction algorithm can be used to obtain the true ATN value from ATN values acquired at different sampling flow rates, and the actual BC mass concentrations can be determined from the true ATN change rate. Before BC correction, the BC concentration measured at the sampling flow rate of 6 L min−1 was smaller than that measured at 2 L min−1 by approximately 13 and 9% in summer and winter seasons, respectively. After BC correction by using the true ATN value, the corrected BC for 6 L min−1 can be exactly equal to the corrected BC for 2 L min−1. Field test results demonstrated that loading effects on BC measurements could be corrected accurately by using the proposed model. Additionally, the problem of enhanced light ATN caused by light scattering at the unloaded filter can be overcome without using any light scattering coefficient. Therefore, the correction algorithm can be applied to a newly designed instrument to determine actual real-time BC concentrations by using two sampling spots for different aerosol deposition rates. Moreover, a simple empirical correction scheme for post-processing for correcting the existed aethalometer BC data is also presented. While this simple correction scheme is dependent on the aerosol type, it can be used to correct BC data when the primary source of BC and the weather conditions are similar to those in this study. Furthermore, two existed aethalometers with appropriate flow control can be used to create correction schemes suitable for different environments.