The NARSTO_EPA_SS_FRESNO_PM25_NO3_SO4 is the North American Research Strategy for Tropospheric Ozone (NARSTO) Environmental Protection Agency (EPA) Supersite (SS) Fresno, Particulate Matter (PM) 2.5 Particulate Nitrate and Sulfate Data. This data set contains measurements taken from two nitrate monitors and one sulfate monitor operated at the Fresno Supersite. The sample collection time for all instruments was 8 minutes. The sample analysis time was 2 minutes. Data were output once every 10 minutes. The Rupprecht and Patashnick (R&P) Ambient Particulate Nitrate Monitor measured the amount of particulate nitrate in an air sample at a nearly continuous rate. The Rupprecht and Patashnick (R&P) Ambient Particulate Sulfate Monitor measured the amount of particulate sulfate in an air sample at a nearly continuous rate. The ambient aerosol was collected by impaction on a small metallic strip. At the end of collection, the strip was heated to vaporize and decompose the particulate matter into oxides which were then measured. The Fresno Supersite is one of several Supersites established in urban areas within the United States by the EPA to better understand the measurement, sources, and health effects of suspended particulate matter (PM). The site is located at 3425 First Street, approximately 1 km north of the downtown commercial district. First Street was a four-lane artery with moderate traffic levels. Commercial establishments, office buildings, churches, and schools were located north and south of the monitor. Medium-density single-family homes and some apartments were located in the blocks to the east and west of First Street. The Fresno Supersite began operation in May of 1999.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.