Application of Density Plots and Time Series Modelling to the Analysis of Nitrogen Dioxides Measured by Low-Cost and Reference Sensors in Urban Areas

Temporal variability of NO2 concentrations measured by 28 Envirowatch E-MOTEs, 13 AQMesh pods, and eight reference sensors (five run Sheffield City Council three the Department for Environment, Food Rural Affairs (DEFRA)) was analysed at different time scales (e.g., annual, weekly diurnal cycles). Density plots variation were used to compare distributions temporal concentrations. Long-term trends, both adjusted non-adjusted, showed significant reductions in At Tinsley site, non-adjusted trend ?0.94 (?1.12, ?0.78) µgm?3/year, whereas ?0.95 (?1.04, ?0.86) µgm?3/year. Devonshire Green, ?1.21 (?1.91, ?0.41) µgm?3/year ?1.26 (?1.57, ?0.83) Furthermore, employing univariate linear nonlinear series models their performance compared with a more advanced model using two exogenous variables (NO O3). For this purpose, data NO, O3 obtained from site Sheffield, which accurate than measurements low-cost and, therefore, suitable training testing model. In article, main steps development are discussed: (i) specification choosing appropriate values p, d q, (ii) fitting (parameters estimation), (iii) diagnostic (testing goodness fit). The auto-regressive integrated moving average (ARIMA) performed better counterpart; however, its predicting concentration inferior ARIMA (ARIMAX). Using cross-validation ARIMAX demonstrated strong association concentrations, correlation coefficient 0.84 RMSE 9.90. can be as an early warning tool potential pollution episodes order proactive adopting precautionary measures.