Observation‐Based Constraints on Anthropogenic Carbonyl Sulfide Emissions in Southeastern China From High‐Frequency Measurements in Urban Guangzhou

Abstract Carbonyl sulfide (COS) is the most abundant sulfur‐containing trace gas in the troposphere and an important tracer of terrestrial gross primary productivity (GPP), but its application is limited by uncertain regional emissions, especially in East Asia. Here we present one year (April 2022–March 2023) of 3‐hourly online COS measurements at an urban receptor site in Guangzhou, south China. The annual mean COS mixing ratio was 599.8 ± 6.2 pptv, while the annual mean urban baseline derived from the lowest 25% of observations in a centered 7‐day moving window was 569.2 ± 5.4 pptv, about 16.1% higher than the remote National Oceanic and Atmospheric Administration baseline at Mauna Loa Observatory on their respective calibration scales. COS exhibited a winter maximum (741.6 ± 7.7 pptv) and a summer minimum (478.1 ± 2.9 pptv). Trajectory clustering indicates that this contrast primarily reflected a monsoon‐driven transition from marine‐influenced transport and stronger ventilation in summer to continental influence and less efficient dispersion in winter; terrestrial uptake may have made a secondary contribution to the summer decline. Weighted potential source contribution function analyses associated elevated COS with industrialized corridors in eastern and southern China, while fire hotspots indicated possible episodic contributions from biomass burning. A CHCl 3 ‐based tracer‐ratio analysis yielded a receptor‐based constraint of 41.0 ± 6.4 Gg yr −1 for the anthropogenic COS emissions in southeastern China that co‐varied with CHCl 3 in air masses reaching Guangzhou. These results provide new observational benchmarks for improving regional COS inventories and for reducing anthropogenic bias in COS‐based estimates of GPP over East Asia.