NARSTO_EPA_SS_LOS_ANGELES_HEADS_PART_IONS_MASS is the North American Research Strategy for Tropospheric Ozone (NARSTO) Environmental Protection Agency (EPA) Supersite (SS) Los Angeles Harvard/EPA Annular Denuder System (HEADS) Data product. This product was collected between December 2001 and June 2003. The HEADS model URG-2000-30DI was used to collect the Particulate Matter (PM) 2.5 mass concentration data episodically from December 6, 2001 - August 21, 2002. It was also used to collect sulfate and nitrate ions at Claremont from September 28, 2001 - August 6, 2002, at Riverside from March 14 - June 6 2001, and the University of Southern California from October 8, 2002 - June 11, 2003. HEADS uses chemically coated annular denuder tubes to selectively remove gaseous pollutants before PM. The overall objective of the Los Angeles Supersite in Southern California Particle Center and Supersite (SCPCS) was to conduct monitoring and research that contributes to a better understanding of the measurement, sources, size distribution, chemical composition and physical state, spatial and temporal variability, and linkages to health effects of airborne particulate matter in the Los Angeles Basin (LAB). 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 these 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.