APPLICATION EVALUATION AND ENSEMBLE IMPROVEMENT OF TWO AIR-QUALITY NUMERICAL MODELS
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摘要: 利用2018—2019年国控站观测,评估CAMx和CMAQ模式对广东珠海主要污染物时空分布与演变特征的预报能力,并引入多元线性回归和随机森林方法对预报结果进行集成,探究不同集合方法的改进能力。结果表明:CMAQ在各污染物浓度季节-日变化方面明显优于CAMx,但两者存在明显系统偏差,并对多数污染物(除O3之外)的昼夜和空间变化的模拟能力仍存在明显缺陷。例如,CMAQ合理地还原了CO、PM2.5、PM10、SO2、O3和NO2的季节变化,相关系数介于0.72~0.84,但NMB分别达到-0.58、-0.18、-0.30、1.52,-0.16和-0.20,RMSE分别达到0.40 mg/m3、6.86、16.02、10.71、25.05和10.21 μg/m3。同时,基于不同污染物构建的两种集合方法均有效移除了系统偏差,加强了CMAQ的模拟优势,并且随机森林方法明显优于多元线性回归,但两者均对模式缺陷无明显改进。进一步分析发现,CMAQ与CAMx模型的重要性基本相当,表明集合方法的预报能力与集合成员的线性偏差无关,主要取决于不同成员的代表性。最后,本研究揭示以随机森林为代表的集合方法虽有效提高了污染物的预报能力,但改进数值模式自身能力和增加具有代表性的集合成员对预报水平的进一步提升十分关键。Abstract: This study evaluated the performances of two numerical air-quality models (i. e., CMAQ and CAMx) for the air pollutants forecast over Zhuhai based on the observations from national stations during 2018-2019. Moreover, two ensemble methods including Multiple Linear Regression (MLR) and Random Forest (RF) were employed to determine their improvement capabilities. The results show that the CMAQ outperformed the CAMx in reproducing the seasonal-daily variations of each air pollutant, but both of them showed obvious systematic biases, and presented poor performances in representing the diurnal and spatial variations of the air pollutants (except O3). For example, the CMAQ reasonably reproduced the seasonal variations of CO, PM2.5, PM10, SO2, O3 and NO2, with correlation coefficients ranging from 0.72 to 0.84, while the NMB (RMSE) reached -0.58 (0.40 mg/m3), -0.18 (6.86 μg/m3), -0.30 (16.02 μg/m3), 1.52 (10.71 μg/m3), -0.16 (25.05 μg/m3) and -0.20 (10.21 μg/m3), respectively. Meanwhile, the MLR and RF models, constructed based on all pollutants, effectively removed the systematic biases, and enhanced the strengths of the CAMx model, with the RF performing better. However, both of them did not improve these model defects much. Further analysis indicates that the impotency of CMAQ and CAMx was comparably important, suggesting that the prediction ability of the ensemble method is mainly related to the representativeness of different members, irrespective of their linear deviations. Finally, this study reveals that despite the effective improvement of the RF in predicting the pollutants, the key for further refinement of predicting capabilities is to improve numerical models'own abilities and incorporate more representative participating members.
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Key words:
- air quality model /
- application evaluation /
- ensemble methods /
- Random Forest
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表 1 CMAQ与CAMx模式设置
模式选项 CMAQ CAMx 气象条件来源 区域GRAPES模式 区域GRAPES模式 排放源清单 多种源清单融合,并结合卫星遥感和观测进行优化 多种源清单融合 网格嵌套模式 三重嵌套,单向 三重嵌套,单向 水平分辨率 27-9-3 km 27-9-3 km 垂直分层数 25 25 水平平流 PPM PPM 垂直对流 PPM 隐式对流 水平扩散 ACM2 ACM2 垂直扩散 涡流扩散 涡流扩散 干沉降 M3DRY WESELY89 气象化学机理 SAPRC07 SAPRC07 气象化学算法 EBI CMC 网格烟雨模块 关闭 关闭 表 2 珠海市六种污染物季节变化统计参数
污染物 RMSE R NMB CAMx CMAQ MLR RF CAMx CMAQ MLR RF CAMx CMAQ MLR RF CO 0.34 0.40 0.08 0.08 0.61 0.77 0.76 0.81 -0.49 -0.58 0.01 0.01 PM2.5 11.02 6.86 6.42 5.17 0.82 0.90 0.91 0.93 -0.33 -0.18 0.01 0.02 PM10 25.28 16.02 10.86 8.68 0.82 0.84 0.85 0.90 -0.53 -0.30 0.01 0.01 SO2 14.16 10.71 1.75 1.57 0.25 0.78 0.71 0.78 1.99 1.52 0.01 0.02 O3 28.56 25.05 25.33 22.44 0.41 0.72 0.73 0.76 -0.15 -0.16 -0.16 -0.12 NO2 27.61 10.21 9.93 9.37 0.49 0.74 0.73 0.78 -0.87 -0.20 0.04 0.05 -
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