###### Abstract  
This study presents a GIS-based method integrating hourly transport pathways and wind-field grid reconstruction, straw open burning (SOB) source identification, and a two-stage spatiotemporal multi-box modeling approach to quantify the contribution of external sources of SOB to elevated urban PM\({}_{2.5}\) concentrations during a specific pollution episode (PE) at a high temporal resolution of 1 h. Taking Jilin Province as an empirical study, the contribution of SOB in province-wide farmlands to urban haze episodes in Changchun during the SOB season of 2020-2021 was evaluated quantitatively using a combination of multi-source datasets. The results showed that Changchun experienced three severe PEs and one heavy PE during the study period, and the total PM\({}_{2.5}\) contributions from SOB sources were 352 ug m\({}^{-3}\), 872 ug m\({}^{-3}\), and 1224 ug m\({}^{-3}\) during the three severe PEs, respectively; these accounted for 7%, 27%, and 23% of the urban cumulative PM\({}_{2.5}\) levels, which were more obvious than the contribution during the PE. The total PM\({}_{2.5}\) contribution from SOB sources (4.9 ug m\({}^{-3}\)) was only 0.31% of the urban cumulative PM\({}_{2.5}\) level during the heavy PE. According to the analysis of the impact of individual factors, some policy suggestions are put forward for refined SOB management, including control spatial scope, burning time interval, as well as burning area limit under different urban and transport pathways' meteorological conditions and different transport distances. s 202214671. 11.111.11.11.11.11.11.11.11.11.11.1.11.11.11.1.11.11.1.11.11.1.11.11.1.11.1.11.11.1.11.1.11.11.1.11.11.1.11.1.11.1.11.1.11.11.1.11.11.11.1.11.11.1.  
time; a considerable amount of straw is still discarded and has to be burned to prepare for planting in the coming spring. Consequently, in order to minimize the impact of SOB on the air quality of urban areas under the premise of ensuring agricultural production and food security, it is essential to burn the discarded straw in a planned and systematic manner, which can further eliminate the conflict between environmental management enforcers and farmers. Therefore, quantitative assessment of the regional transport of straw burning-sourced PM\({}_{2.5}\) in rural areas and its contribution to urban haze episodes has significance for implementing targeted emission-control measures. Several methods have been applied to estimate the impacts of external particulate sources on local air quality. Backward trajectory analysis is one of the most commonly used methods for analyzing pollution episodes and tracing the historical location of air masses passing over to identify their potential external sources. Backward trajectory modeling, combined with atmospheric concentrations at the receptor site, generally includes the potential source contribution function (PSCF) [13; 14], gridded frequency distributions (GFD) [15], concentration-field analysis, concentration-weighted trajectory (CWT) [16], trajectory clustering analysis, residence-time-weighted concentration (RTWC) [13; 17], and conditional probability function (CPF) [18]. All these models are essentially statistical analyses of many (over months to years) trajectories by counting the frequency of back-trajectory segment endpoints in grid cells to show the geographic origin most associated with elevated concentrations among long-term air pollution measurement data [19]. However, they cannot quantify the regional transport mass or concentration of PM\({}_{2.5}\). Another commonly used approach is based on air quality models such as WRF-CMAQ, WRF-CAMx, and WRF-CHEM, including sensitivity analysis [20; 21; 22] and transport flux approaches [23; 24; 25], among others [26; 27; 28]. The characteristics of the transport pollutant and its contribution to high particulate pollution can be quantified using computational atmospheric models.