Atmospheric pollution in Ukraine (2022-2023): role of fires in CO, NO2, and aerosol emissions during two years of military conflict

More than two years of hostilities, which began on the 24th of February 2022 with the invasion by Russian armed forces into Ukraine, have altered the emission patterns by destructing industrial facilities and the emerging new local pollution sources from military actions and missile strikes. In this respect, we discuss the changes in air quality across Ukraine during the first two years of the conflict (2022–2023), with a specific focus on fires as a key contributor to pollution. To facilitate spatial and temporal analysis, we distinguish eight regions within the territory of  Ukraine, which makes it possible to map the extent and magnitude of fire-related emissions and track their evolution in response to the changes in the front-line location. We utilized data from the European Forest Fire Information System (EFFIS), specifically the MODIS/SENTINEL-2 Burnt Areas product, to identify the extent of burnt areas, analyze fire activity, categorize affected land cover types, and assess the resulting influence on atmospheric pollution levels. To link fire episodes with pollution, we used Sentinel-5 Precursor (S5P) TROPOMI Level 2 data for tropospheric NO₂, CO, and the Absorbing Aerosol Index (AAI). Additionally, we incorporated ground-based observations from the Ukrainian National Air Quality Network (NAQN), a system of about 100 monitoring stations in 39 cities across Ukraine that measure atmospheric chemicals, which has not been done before. 

It was found that in Ukraine in 2022, the war was a major driver of fire activity, with 66% of the total burned area located within a 30-km zone along the front line. In 2023, this proportion increased to nearly 80% within the same 30-km zone. The retrieved satellite emissions showed that peak fire activity was accompanied by increases in NO₂, CO, and aerosol concentrations, which exceeded the historical daily maxima for 2018-2021. Ground-based observations showed mixed tendencies, with concentrations decreasing in 16 cities and significantly rising in others (9 cities). The proximity of monitoring stations to industrial sources complicates the ability to isolate air quality changes that were not directly caused by industry or industrial destruction. Only Sloviansk (Donetsk region, located 20-30 km from the front line) showed reliable increases in NO₂, CO, and dust concentrations, which could be directly attributed to military activities. To demonstrate the contribution of increased fire activity to atmospheric pollution, we compared biomass burning emissions, based on fire radiative power, with anthropogenic emission inventories from periods before and during the hostilities. During severe fire seasons (2020, 2022, and 2023), both the Copernicus Atmosphere Monitoring Service (CAMS) and Global Fire Assimilation System (GFAS) inventories reported comparable NO_x emission levels, while CO emissions increased by up to 11-fold. In contrast, during a milder fire season (2021), NO_x emissions were 2.5 times lower than industrial emissions, whereas CO levels were similar to or slightly exceeded those from industrial sources. This evidence suggests that in Ukraine, pollution from fires, also caused by war, can be as significant as emissions from industrial sources, depending on the intensity of the fire season.