Figure 11.

Summary of ridge traces of the top 10 most important parameters from the regression of each pollutant. These pollutants were (a) NO₂, (b) CO, (c) NMHC, (d) Gasoline, (e) CO₂, and (f) CH₄. Weight magnitude should not be compared between compounds because they scale with the concentration values. Interactions with temperature and/or humidity are indicated by “:T”, “:H”, or “:T:H, respectively. Colors indicate the sensor and are sorted from largest to smallest importance at high regularization. Dashed lines illustrate the ridge trace for each cross-validation fold, and the solid lines illustrate the median value for all folds. The x-axis of each plot indicates the ridge parameter (regularization strength), and the y-axis indicates the unbiased parameter weight. Larger absolute values indicate a stronger importance of that sensor, especially at larger values of the ridge parameter.