Annual trends (top) and day of week patterns (bottom) in difference in mole fractions of 24-hour average NOx and concentrations of PM2.5 (ΔC) in Fresno, CA using the multiple linear regression model. Winter months shown on the left, summer months on the right, holidays (“Hol”) are defined in the text. DOI: https://doi.org/10.1525/elementa.384.f3