T119 EPA PM2.5 scheduled-observation completeness data and code

Versioned data and code supporting a reproducible analysis of scheduled-observation completeness and analytic-panel retention across 27 U.S. EPA AirData annual PM2.5 monitor archives from 1999 through 2025. The package contains frozen protocols, 27 exact source archives with provenance and hashes, derived site-POC-year and site-year products, primary and independent implementations, validation artifacts, figure source data, environment records, failed-run audit history, and a one-command reproduction runner. The locked 2021-2024 finite cohort contains all 392 eligible repeated sites, of which 169 (43.1%) switched across the 90% maximum-POC completeness category. The results concern archive-defined record completeness and do not establish pollution, exposure, health, equipment failure, missingness mechanisms, regulatory compliance, design values, population representativeness, or causation.