Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA.
Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Sensors (Basel). 2020 Nov 24;20(23):6714. doi: 10.3390/s20236714.
The exhaust plume capture method is a commonly used approach to measure pollutants emitted by in-use heavy-duty diesel trucks. Lower cost sensors, if used in place of traditional research-grade analyzers, could enable wider application of this method, including use as a monitoring tool to identify high-emitting trucks that may warrant inspection and maintenance. However, low-cost sensors have for the most part only been evaluated under ambient conditions as opposed to source-influenced environments with rapidly changing pollutant concentrations. This study compared black carbon (BC) emission factors determined using different BC and carbon dioxide (CO) sensors that range in cost from $200 to $20,000. Controlled laboratory experiments show that traditional zero and span steady-state calibration checks are not robust indicators of sensor performance when sampling short duration concentration peaks. Fleet BC emission factor distributions measured at two locations at the Port of Oakland in California with 16 BC/CO sensor pairs were similar, but unique sensor pairs identified different high-emitting trucks. At one location, the low-cost PP Systems SBA-5 agreed on the classification of 90% of the high emitters identified by the LI-COR LI-7000 when both were paired with the Magee Scientific AE33. Conversely, lower cost BC sensors when paired with the LI-7000 misclassified more than 50% of high emitters when compared to the AE33/LI-7000. Confidence in emission factor quantification and high-emitter identification improves with larger integrated peak areas of CO and especially BC. This work highlights that sensor evaluation should be conducted under application-specific conditions, whether that be for ambient air monitoring or source characterization.
尾气羽流捕集法是一种常用于测量在用重型柴油卡车排放污染物的方法。如果使用低成本传感器代替传统的研究级分析仪，这种方法的应用范围可能会更广，包括将其作为一种监测工具，以识别可能需要检查和维护的高排放卡车。然而，低成本传感器在很大程度上仅在环境条件下进行了评估，而不是在污染源影响的环境中进行评估，因为在污染源影响的环境中，污染物浓度会迅速变化。本研究比较了不同的黑碳（BC）和二氧化碳（CO）传感器在成本上从 200 美元到 20000 美元之间的 BC 排放因子，这些传感器的范围从 200 美元到 20000 美元不等。受控实验室实验表明，当采样短时间浓度峰值时，传统的零点和跨度稳态校准检查不是传感器性能的可靠指标。在加利福尼亚州奥克兰港的两个地点使用 16 对 BC/CO 传感器对车队的 BC 排放因子分布进行了测量，结果表明，虽然分布相似，但独特的传感器对确定不同的高排放卡车有不同的结果。在一个地点，当与 Magee Scientific AE33 配对时，低成本的 PP Systems SBA-5 与 LI-COR LI-7000 对 90%的高排放物的分类结果一致，而当与 LI-7000 配对时，低成本的 BC 传感器对高排放物的分类错误超过 50%，而与 AE33/LI-7000 配对时则不会。随着 CO 特别是 BC 的积分峰值面积增大，排放因子定量和高排放物识别的置信度提高。这项工作强调，无论是在环境空气监测还是在源特性化方面，传感器评估都应在特定应用条件下进行。
