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Evaluation of Analysis by Cross-Validation, Part II: Diagnostic and Optimization of Analysis Error Covariance
Open AccessArticle

Evaluation of Analysis by Cross-Validation. Part I: Using Verification Metrics

Air Quality Research Division, Environment and Climate Change Canada, 2121 Transcanada Highway, Dorval, QC H9P 1J3, Canada
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Atmosphere 2018, 9(3), 86; https://doi.org/10.3390/atmos9030086
Received: 5 September 2017 / Revised: 20 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
(This article belongs to the Special Issue Air Quality Monitoring and Forecasting)
We examine how passive and active observations are useful to evaluate an air quality analysis. By leaving out observations from the analysis, we form passive observations, and the observations used in the analysis are called active observations. We evaluated the surface air quality analysis of O3 and PM2.5 against passive and active observations using standard model verification metrics such as bias, fractional bias, fraction of correct within a factor of 2, correlation and variance. The results show that verification of analyses against active observations always give an overestimation of the correlation and an underestimation of the variance. Evaluation against passive or any independent observations display a minimum of variance and maximum of correlation as we vary the observation weight, thus providing a mean to obtain the optimal observation weight. For the time and dates considered, the correlation between (independent) observations and the model is 0.55 for O3 and 0.3 for PM2.5 and for the analysis, with optimal observation weight, increases to 0.74 for O3 and 0.54 for PM2.5. We show that bias can be a misleading measure of evaluation and recommend the use of a fractional bias such as the modified normalized mean bias (MNMB). An evaluation of the model bias and variance as a function of model values also show a clear linear dependence with the model values for both O3 and PM2.5. View Full-Text
Keywords: chemical data assimilation; air quality model diagnostics; cross-validation chemical data assimilation; air quality model diagnostics; cross-validation
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MDPI and ACS Style

Ménard, R.; Deshaies-Jacques, M. Evaluation of Analysis by Cross-Validation. Part I: Using Verification Metrics. Atmosphere 2018, 9, 86. https://doi.org/10.3390/atmos9030086

AMA Style

Ménard R, Deshaies-Jacques M. Evaluation of Analysis by Cross-Validation. Part I: Using Verification Metrics. Atmosphere. 2018; 9(3):86. https://doi.org/10.3390/atmos9030086

Chicago/Turabian Style

Ménard, Richard; Deshaies-Jacques, Martin. 2018. "Evaluation of Analysis by Cross-Validation. Part I: Using Verification Metrics" Atmosphere 9, no. 3: 86. https://doi.org/10.3390/atmos9030086

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