Facility-wide greenhouse gas and pollutant emissions from covered aerated static pile composting

This study presents one of the first facility-wide assessments of greenhouse gas (CH₄, N₂O, CO₂) and air pollutant (NH₃, H₂S, NMVOCs) emissions from a full-scale covered aerated static pile (CASP) composting facility in Napa, California. Emissions were quantified using dynamic flux chambers and unmanned aerial vehicle (UAV)-based flux curtain (CH₄ only) methods during four seasonal campaigns. Facility-wide climate forcing emissions were 66,000 ± 5,000 Mg CO₂-eq. yr^-1 (0.55 ± 0.04 Mg CO₂-eq. Mg^-1 wet waste), dominated by CO₂ (approximately 85%), with smaller contributions from CH₄ (approximately 10%), N₂O (approximately 2%), and NMVOCs (approximately 3%). The CASP phase was the main source of CH₄ (65%), followed by curing (28%) and feedstock piles (4%). Fluxes were primarily governed by operational phase, with secondary effects from season and spatial variabilities. UAV-based CH₄ estimates were approximately 50% lower than chamber extrapolations, highlighting bias when scaling point measurements to facility level. Results provide updated emission factors for aerobic composting and identify operational drivers-including moisture, aeration uniformity, and pile geometry-that strongly influence emissions. The findings inform best practices for composting operations and support improved greenhouse gas inventories, life cycle assessments, and climate policies.