Project Abstract Today, more than 20 years after the 9/11 terrorist attacks, many exposed community members continue to have persistent lower airway symptoms with functional abnormalities in large and/or small airways as indicated by spirometry measures of airflow and/or oscillometry measures of airway heterogeneity. Prior studies and knowledges have been focused on the health effects of World Trade Center (WTC) exposures on the average lung function profiles or discrete lung function patterns, however, systematic investigations on the severe spectrum of the disease are limited. Post-bronchodilator (BD) measurements may identify persistent lung injury as residual airflow limitation with significant morbidity and reduced quality of life, and thus are important and clinically relevant parameters to investigate. Moreover, it is of key public health importance to study the heterogeneous health impacts of the disaster and disparities in healthcare and wellbeing within subgroups. In this project, we propose to address the important scientific questions related to respiratory disease in WTC Survivor population and within vulnerable subgroups, through the following aims: Aim 1: Evaluate the extreme quantiles of cross-sectional measurements of post-BD airway function, including large and small airway metrics, and their association with WTC exposures and comorbidities. Aim 2: Conduct longitudinal quantile analysis to investigate WTC exposures and other risk factors as determinants of the trajectory of extreme quantiles of post-BD large and small airway metrics. Aim 3: Identify and evaluate vulnerable subgroups who show heterogeneous susceptibilities to WTC exposures. Upon its completion, the proposed project will expand our knowledge about health effects on severe respiratory diseases related to the 9/11 terrorist attacks, help to answer complex interplays of physical and mental health comorbidities, and apply lessons to the management of disaster events.