The aim of the study is to characterize the impact of deployment-related pollution exposures during the Post-9/11 Gulf War Era on current respiratory health using objectively ascertained and standardized physiologic and epidemiologic measures. The primary objective in support of this aim is to assess the association of cumulative exposure to PM2.5 during deployments to the U.S. bases and other locations in Central Asia (Afghanistan and Kyrgyzstan), Southwest Asia (Iraq, Kuwait, Qatar, and United Arab Emirates) and Africa (Djibouti) with current measures of pulmonary function. Secondary objectives in support of the aim will examine the association of cumulative exposure to PM2.5 during deployments with the clinical outcome of medically-treated asthma. The investigators will also explore the impact of deployment duration on both pulmonary function and asthma.