Purpose <p>Given the fluctuations in ambient PM_2.5 and the varying classroom activities, traditional monitoring methods may be impractical for assessing long-term indoor PM_2.5 exposures among schoolchildren due to the substantial sample size required. Although the well-mixed room (WMR) model offers a potential solution, it first requires quantifying the indoor PM_2.5 generation rate (G) and the non-ventilation removal rate (K). This study presents a technique to simultaneously estimate both G and K using a combination of numerical and iterative methods and applies the results to WMR for predicting PM_2.5 concentrations inside the classroom.</p> Methods <p>The whole study was conducted in a typical elementary school classroom equipped with two fresh air units (FAUs) and four electric fans. PM_2.5 and CO₂ concentrations were measured simultaneously inside and outside the classroom.</p> Results <p>The PM_2.5 generation rate, G (GM (GSD)), was estimated at 10.7 (2.1) µg min⁻¹ during lecture sessions and 19.2 (1.2) µg min⁻¹ during the noon rest period. However, the non-ventilation removal rate, K, was consistently found to be 0.&#xa0;Activity intensity significantly influenced the magnitude of G. Higher-intensity activities, such as extensive chalk usage, resulted in elevated G values compared to lower-intensity activities, such as quizzes. Noon rest periods exhibited notably higher G values, likely due to diverse student activities, including eating and walking. The consistent absence of K may be attributed to the small particle size of PM_2.5.&#xa0;No significant differences were observed between measured and model-predicted PM_2.5 levels inside the classroom.</p> Conclusions <p>These findings suggest that the developed technique is practical and effective for quantifying both G and K, supporting the use of the WMR modeling approach for estimating long-term classroom PM_2.5 concentrations for schoolchildren.</p> Graphical Abstract <p></p>