The NARSTO_EPA_SS_BALTIMORE_JHU_MET_DATA is the North American Research Strategy for Tropospheric Ozone (NARSTO) Environmental Protection Agency (EPA) Supersite (SS) Baltimore, Johns Hopkins University (JHU) LIDAR Backscatter and Mixing Height Data product. This product contains measurements that were taken from May 2001 to September 2002 during the Baltimore Experiment of the EPA Particulate Matter (PM) Supersites Program by the JHU, Department of Geography and Environmental Engineering. A miniature elastic backscatter LIDAR was operated at several Baltimore locations in the vertical mode with typical resolution range of 3 m, typical time steps of 5 seconds, and ranges of 4.5-8 km. All vertical profile measurements of aerosol backscatter were taken during daytime with continuous sampling and can be used to describe composition, dynamics, and extent of the mixing layer and the air aloft. Mixing heights were determined from profile data under cloud-free conditions. Included in this data set are the large ASCII files of the aerosol backscatter data, the calculated mixing height data, and a companion HTML application with color images of the LIDAR profiles of the backscatter signals from aerosols. The EPA PM Supersites Program was an ambient air monitoring research program from 1999-2004 designed to provide information of value to the atmospheric sciences, and human health and exposure research communities. The EPA PM Supersites Program was an ambient air monitoring research program designed to provide information of value to the atmospheric sciences, and human health and exposure research communities. Eight geographically diverse projects were chosen to specifically address the following EPA research priorities: (1) to characterize PM, its constituents, precursors, co-pollutants, atmospheric transport, and its source categories that affect the PM in any region; (2) to address the research questions and scientific uncertainties about PM source-receptor and exposure-health effects relationships; and (3) to compare and evaluate different methods of characterizing PM including testing new and emerging measurement methods.NARSTO, which has since disbanded, was a public/private partnership, whose membership spanned across government, utilities, industry, and academe throughout Mexico, the United States, and Canada. The primary mission was to coordinate and enhance policy-relevant scientific research and assessment of tropospheric pollution behavior; activities provide input for science-based decision-making and determination of workable, efficient, and effective strategies for local and regional air-pollution management. Data products from local, regional, and international monitoring and research programs are still available.