Impact of agricultural sources on NH3 and PM levels in the South-Central Anatolia

Abstract

Atmospheric ammonia (NH3) is an important component of the nitrogen cycle and rapidly reacts with acidic compounds such as sulfuric acid (H2SO4) and nitric acid (HNO3) in the atmosphere to form secondary inorganic aerosols (SIA). Thus, NH3 plays a major role in the formation of secondary fine particulate matter (PM2.5). These fine particles penetrate deeply into the respiratory system, causing serious health problems, cardiovascular and respiratory diseases, and premature death. In addition, in regions where NH3 emissions are high, environmental problems such as acidification and eutrophication occur as a result of excessive nitrogen loading in ecosystems. Considering contribution of NH3 to PM formation, its impact on human health, and its direct role in environmental problems, strategies for its reduction should be developed. The main sources of NH3 emissions are agricultural activities. The contribution of agricultural activities to worldwide NH3 emissions is around 80-90%. Agricultural activities include mainly manure and urine released from livestock activities, application of organic and synthetic nitrogenous fertilizers, storage of fertilizers, and open burning of agricultural waste. NH3 released into the atmosphere from animal waste increases especially when manures are left open and not properly processed. Synthetic fertilizers, especially urea-based, can rapidly transformed to NH3 through hydrolysis after application to the soil and release into the atmosphere through volatilization. Although open burning of agricultural waste contributes to NH3 emissions to a limited extent, it can lead to local hotspots if more than one event occurs regionally during specific periods. These emissions may vary depending on meteorological factors such as temperature, wind, relative humidity, and precipitation. NH3 levels are observed significantly higher in some regions in Türkiye. The regions with high NH3 levels are; İzmir and its surroundings, Iğdır, Mersin and Adana in the Eastern Mediterranean, and Konya and its surroundings in Central Anatolia. It is important to examine NH3 levels, and analyze the sources in Konya and its surroundings, which is the region with the most intensive agricultural activities in Türkiye. Within the scope of this thesis, it is aimed to determine the effects of agricultural sources on NH3 and PM in the provinces of Konya, Karaman, Aksaray and Nigde in the Southern Central Anatolia. The aim of the study is to analyze the spatial and temporal variation of NH3 levels originating from agricultural activities in the region in the long term (2012-2023), to examine the effects of agricultural sources and to determine the relationship of NH3 with PM, and atmospheric conditions and to establish a scientific basis for understanding NH3 levels in Türkiye. Satellite-based NH3 measurements and ground-based PM measurements were used to evaluate pollution in the study region: Konya and its surroundings. NH3 data were obtained from Level-2 IASI retrievals of IASI instrument on the Meteorological Operational Satellite (METOP) A/B/C satellites developed by the European Space Agency (ESA). The data between the years of 2012-2023 were processed temporally and spatially into 4×4 and 1×1 km2 gridded system created within the scope of this study. With the obtained data sets, monthly, seasonal and annual changes in NH3 levels were examined spatially and temporally. In order to see the effect of agricultural activities, NH3 levels in different land types were examined with Coordination of Information on the Environment (CORINE) Land Cover (CLC) definitions. In addition, in order to understand the effect of agricultural waste burning on high NH3 and PM levels in the fall season, biomass burning areas were determined with VIIRS S-NPP Fire Radiative Power (FRP) product, and aerosol types were examined using CALIOP Level-2 the vertical feature mask (VFM) product. PM data were obtained from ground-based air quality monitoring stations (AQMS) from national monitoring network and meteorological data were obtained from ground-based meteorological stations (MS) from Turkish State Meteorological Service (TSMS) in the region. Additionally, population density data (GHSL-POP) and the region's topographic structure using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model (DEM) data were analyzed to understand and evaluate NH3 and PM levels. All these data were processed and subjected to spatial analysis to ensure same spatial and temporal resolution. To assess long-term NH3 trends and their spatial-temporal dynamics, the Seasonal Mann-Kendall test was applied to daily satellite-based NH3 data (2012-2023) across four provinces, separately for all land covers and agricultural areas. Also, to better understand the spatiotemporal variability and NH3 levels dynamics across the study area, spatial clustering based on daily NH3 values was performed using hierarchical clustering after KNN imputation. Optimal cluster numbers were identified via the Elbow Method and KneeLocator algorithm (k=5 for 2012-2023; k=7 for 2020-2023), ensuring meaningful separation between distinct NH3 profiles. Additionally, Geographically Weighted Regression (GWR) was used to analyze the spatially varying relationship between NH3 and PM2.5 concentrations, providing insights into how these atmospheric pollutants vary across the region. A significant increasing trend in NH3 levels was observed in the Southern Central Anatolia Region between 2012 and 2023. While the annual average NH3 level in 2012 was 3.1×1015 molecules/cm2, this value increased by 24.4% in 2020 and reached 5.1×1015 molecules/cm2, the highest level in the 12-year period. In 2021 and 2022, the levels remained close to this high level at 4.9 and 5.0×1015 molecules/cm2. In 2023, it decreased slightly to 4.7×1015 molecules/cm2. In agricultural areas, average NH3 levels are significantly higher than the all area average. For example, in 2020, average NH3 level in agricultural area was 5.5×1015 molecules/cm2, 7.8% higher than the average in the all area. At the provincial basis, Aksaray has the highest annual average NH3 levels, followed by Konya, Nigde, and Karaman. However, in terms of extreme values, for example, the 99.9th percentile value in Konya in 2020 is 9.7% higher than Aksaray. The highest annual average NH3 levels in districts were observed in Konya–Eregli (9.9×1015 molecules/cm2 in 2021), Konya-Karapinar, Konya-Emirgazi, Nigde-Bor, Aksaray-Sultanhani, and Konya-Meram districts, respectively. In seasonal distribution, summer has the highest NH3 levels every year. Especially in the summer of 2022, the average level in agricultural areas reached 7.3×1015 molecules/cm2, marking the highest value recorded. Spring is generally in second place, but fall averages exceeded spring in 2021 and 2023. For example, in 2021, the fall average in agricultural areas was 6.0×1015 molecules/cm2, while it was 5.0×1015 molecules/cm2 in spring. This situation shows that additional NH3 sources such as post-harvest activities (agricultural waste burning), accumulation of animal manure or late-term fertilizer applications are effective in fall. According to the Mann-Kendall trend analysis, a statistically significant increase in NH3 levels was observed in both all area and agricultural area analysis during the 2012-2023 period (p < 0.05). The highest increase was detected in Aksaray, while the lowest was detected in Konya. Cluster analyses revealed that permanent hotspots were formed in regions where agriculture and animal husbandry are intensive, such as Eregli. NH3 concentrations were both highly variable spatially, and showed a stable increase over time. This situation clearly revealed the impact of local sources and land use types on NH3 pollution. To investigate high NH3 levels observed during the fall season, fire activities in the region were analyzed. It was found that fires were more intense throughout all seasons in 2020, followed by the years 2023 and 2019. Seasonally, total fire intensity was highest during fall, followed by summer season. Total fire intensity was relatively low in winter and spring; however, fire activities in winter were higher than expected due to fall fires extending into December. Most of these fires occurred in agricultural areas, suggesting a link between increased fall fires and agricultural residue burning events after harvest. Fires mostly intensify between September and December, but they start to increase at different times in different regions. Particularly in regions such as Konya-Celtik, where sugar beet is extensively cultivated, higher fire emissions corresponded spatially with elevated NH3 levels. In addition, when the NH3 averages in the selected fire-intensive regions (Celtik, Beysehir, Eskil and Konya central and surrounding areas) were mapped between 10 October and 18 November 2022, it was determined that high NH3 levels spatially overlapped with the areas where these fires occurred. This showed that agricultural residue burning makes a noticeable contribution to NH3 emissions in the region, especially in the fall season. To examine the impact of fires on PM, CALIOP retrievals during fire periods were analyzed for 2019-2023. In some scans passing over fire areas, polluted continental aerosols from low radiative power fires were detected. In addition, the study provided a detailed evaluation of PM pollution in the region, showing that PM10 and PM2.5 concentrations frequently exceeded national and international limits. Spatial and directional analyses indicated that agricultural lands, urban zones, livestock farms, and post-harvest fires contributed to PM concentrations. While NH3 and PM2.5 showed a seasonal mismatch, spring and fall exhibited partial alignment, suggesting a conditional link between agricultural ammonia emissions and possible secondary PM formation. Geographically Weighted Regression (GWR) analysis confirmed that NH3 plays a considerable role in PM2.5 variability in livestock-intensive and fire-related areas. Seasonal decoupling between NH3 and PM2.5, especially during winter and summer, emphasized that PM2.5 formation depends not only on NH3 but also on the presence of other precursors, favorable meteorological conditions, and other primary sources. In summary, it was revealed that agricultural activities seriously affect the air quality in the region, and strategies such as management of fertilizer applications, development or improvement of animal manure processing methods and control of open agricultural waste burning are important to reduce this impact. This study provides important scientific findings for the development of policies and measures in agricultural sector to improve air quality in Southern Central Anatolia.