City-scale calibration of a low-cost PM2.5 network for regulatory-compliant air-quality assessment
Fig 5
Spatial and temporal variability of PM2.5 concentrations across the InfoAer and RNMCA monitoring networks.
(a) Deviation from the network-mean number of EU daily PM2.5 threshold exceedances for stations from both monitoring networks. σ represents the standard deviation of annual exceedance frequencies across all InfoAer stations in 2024. δ denotes the deviation of individual InfoAer and RNMCA site exceedance counts from the network-wide mean. The administrative boundaries of Bucharest’s six districts are delineated by purple lines. The base map data was obtained from OpenStreetMap as described in the caption of Fig 1. (b) Monthly-averaged PM2.5 concentrations across the combined dataset. The shaded regions represent the ± 0.5 (dark orange) and ±1.5 (light orange) standard deviation confidence bands around the monthly means.