Highlights 25 -First Land Use Regression using D-STEM, a recently introduced statistical software 26 -Assess D-STEM in spatiotemporal modeling, mapping, and missing data imputation 27 -Estimate high resolution (20x20 m) daily maps for exposure assessment in a megacity 28 -Provide both short-and long-term exposure assessment for epidemiological studies 29 30 31 32 Graphical Abstract 33 34 35 3 Abstract 36 Land use regression (LUR) has been widely applied in epidemiologic research for exposure assessment. 37 In this study, for the first time, we aimed to develop a spatiotemporal LUR model using Distributed 38 Space Time Expectation Maximization (D-STEM). This spatiotemporal LUR model examined with daily 39 particulate matter ≤ 2.5 µm (PM2.5) within the megacity of Tehran, capital of Iran. Moreover, D-STEM 40 missing data imputation was compared with mean substitution in each monitoring station, as it is 41 equivalent to ignoring of missing data, which is common in LUR studies that employ regulatory 42 monitoring stations' data. The amount of missing data was 28% of the total number of observations, in 43 Tehran in 2015. The annual mean of PM2.5 concentrations was 33 µg/m 3 . Spatiotemporal R-squared of 44 the D-STEM final daily LUR model was 78%, and leave-one-out cross-validation (LOOCV) R-squared was 45 66%. Spatial R-squared and LOOCV R-squared were 89% and 72%, respectively. Temporal R-squared and 46 LOOCV R-squared were 99.5% and 99.3%, respectively. Mean absolute error decreased 26% in 47 imputation of missing data by using the D-STEM final LUR model instead of mean substitution. This 48 study reveals competence of the D-STEM software in spatiotemporal missing data imputation, 49 estimation of temporal trend, and mapping of small scale (20 x 20 meters) within-city spatial variations, 50 in the LUR context. The estimated PM2.5 concentrations maps could be used in future studies on short-51 and/or long-term health effects. Overall, we suggest using D-STEM capabilities in increasing LUR studies 52 that employ data of regulatory network monitoring stations. 53 54 55 Keywords 56 Air pollution; D-STEM; LUR; Missing data; PM2.5 57 58 4