Seasonal and interannual variability of atmospheric ammonia over Guatemala driven by land use, biomass burning, and meteorological circulation

Abstract. Ammonia (NH₃) is a key atmospheric precursor of fine particulate matter and a marker of agricultural and biomass burning emissions. In Central America, NH₃ variability remains largely unquantified. This study presents the first integrated spatiotemporal assessment of atmospheric NH₃ over Guatemala (2015–2023) using multi-satellite observations (IASI A/B/C), combined with MODIS fire data, Sentinel-2 land cover, ERA5 meteorology, and CAMS reanalysis. Annual median NH₃ columns remained relatively stable, reflecting persistent agricultural sources dominated by fertilizer use and livestock. Significant anomalies occurred in 2016, 2020, and 2023, with 2020 showing the highest annual and monthly NH₃ levels. Seasonal peaks in April–May coincided with the regional fire season, followed by a sharp decline after rainfall onset. Hotspots were consistently detected in northern (Petén–Quiché) and southern (Escuintla) agricultural regions. The most extreme episode in April 2020 recorded 957 active fires over ~1,486 km², largely within the Maya Biosphere Reserve. Elevated temperature (+ 0.3 °C above the 2015–2023 mean) and high precipitation (+ 17 % above average) favored NH₃ accumulation despite reduced anthropogenic activity during the COVID-19 lockdown. These results indicate that Guatemala’s NH₃ variability is shaped by a stable agricultural baseline with superimposed fire-driven peaks, modulated by climatic anomalies. Continuous satellite monitoring is essential to improve emission inventories and support strategies to reduce biomass burning impacts across Central America.