Forced vital capacity (FVC) of children in the age group 10–12 years are reported as a function of quantum increase in PM_2.5 level in ambient air. The data are reported for the children in the categories based on their respective body mass index (BMI). FVC (% predicted) values decreased with increasing level of PM_2.5. The subjects are found to respond in a selective manner as plateau was observed for FVC values against some selected ranges of PM_2.5 concentration levels (74 µgm⁻³ to >117 µgm⁻³). To explain this unusual behavior, sac theory is proposed which explains the observations of FVC for subjects of all categories with different BMI values.

据报道，年龄在10至12岁之间的儿童的强制肺活量（FVC）与周围空气中PM _2.5含量的量子增加有关。根据儿童各自的体重指数（BMI）报告类别中儿童的数据。FVC（预测的百分比）值随着PM _2.5含量的增加而降低。发现受试者表现出选择性的反应，因为观察到针对某些选定范围的PM _2.5浓度水平（74 µgm ^-3至> 117 µgm ^-3）的FVC值处于平稳状态。为了解释这种异常行为，提出了sac理论，该理论解释了FVC对于具有不同BMI值的所有类别的受试者的观察结果。