Evaluation of IASI NH3 levels in the Eastern Mediterranean Region

Abstract

Air pollution is a growing environmental problem due to its impact on both climate change and public health with increasing population, industrial activity, and agricultural intensification, atmospheric pollutants continue to rise, making effective monitoring more critical than ever. Among these pollutants, ammonia (NH3) remains under-regulated despite its substantial role in air quality degradation and secondary particulate matter (PM) formation. NH3 is an alkaline gas that reacts with atmospheric acids such as nitric acid (HNO3) and sulfuric acid (H2SO4) which can be contribute to the formation of ammonium nitrate (NH4NO3) and ammonium sulfate ((NH4)2SO4) contributing to secondary inorganic aerosols (SIA). These compounds make up a significant portion of secondary fine particulate matter (PM2.5) in atmosphere, which is associated with adverse health effects and contributes to radiative forcing. Agriculture is known as the leading contributor to global atmospheric NH3 emissions, primarily from agricultural activities and animal husbandry, such as livestock housing, manure handling, application of manure and synthetic nitrogen-based fertilizers to land. Beyond agriculture, industrial activities such as fertilizer and soda ash production, as well as NOX reduction processes, also emit NH3. Furthermore, waste management and wastewater treatment systems are additional contributors as well. Biomass burning (BB), which includes wildfires and agricultural residue burning, is another notable source, especially during the smoldering stage of combustion, where NH3 is released alongside CO and other fire-related pollutants. NH3 has been studied using both ground-based and satellite-based approaches. While ground-based measurements provide detailed temporal analyses, satellite retrievals from Infrared Atmospheric Sounding Interferometer (IASI) made it possible to identify global NH3 hotspots and major point sources, especially those related to agricultural and industrial activities. Beyond these well-known sources, BB has been recognized as an important episodic contributor to atmospheric NH3 levels. Several global studies have identified increases in NH3 levels during wildfire events, along with other co-emitted air pollutants such as CO. These studies have reported NH3 peaks via satellite observations, fire-period enhancement ratios, and short-term increases in total column concentrations. However, although BB-related NH3 emissions have been investigated in global studies, research specific to Türkiye remains limited. While some national and regional studies have addressed NH3 pollution using satellite observations, the link between BB and NH3 has not yet been comprehensively examined. This gap is particularly important for the Eastern Mediterranean Region, where BB is a common event due to both the increasing frequency of wildfires driven by climate change, and the widespread practice of agricultural residue burning, despite being officially banned. Therefore, this region represents a critical area for investigating NH3 enhancements associated with BB. In this thesis, satellite-based retrievals of NH3 and CO from IASI and NO2, HCHO, and CO from TROPOMI, and the Fire Radiative Power (FRP) product from Visible Infrared Imaging Radiometer Suite (VIIRS) were used to investigate the relationship between BB events and atmospheric NH3 in the Eastern Mediterranean Region of Türkiye. The study focused on quantifying NH3 enhancement ratios during selected BB episodes and sub-regions via fire-related co-emitted pollutants, including IASI-CO and TROPOspheric Monitoring Instrument (TROPOMI) TROP-NO2, TROP-CO, and TROP-HCHO. Additionally, potential marine impacts were assessed through chlorophyll-a retrievals from (Global Change Observation Mission) GCOM-C over the Mediterranean Sea to investigate the influence of BB-related smoke deposition. The analysis of IASI-NH3 retrievals from 2012 to 2023 over the Eastern Mediterranean region showed consistently high concentrations in coastal provinces such as Mersin and Adana, and relatively elevated levels in Antalya. Seasonal distributions revealed NH3 peaks during spring and summer (>2×1016 molecules/cm2), particularly in agricultural areas such as Silifke, Karatas, and central Mersin, suggesting strong links to seasonal agricultural activity. In fall, elevated NH3 levels were also observed, which were further investigated in relation to BB events. Both spatial distributions and time series analysis showed increasing NH3 levels over the years, and Mann Kendall trend analysis confirmed these patterns with statistically significant increases in all provinces. This long-term trend analysis revealed that NH3 levels increased more rapidly in agricultural zones compared to overall region. Adana showed the highest trend slope in agricultural areas (1.74x1014 molecules/cm2/year). Similar trends were detected in Antalya, Hatay, and Mersin and the slope for agricultural areas nearly twice the overall trend. Further, to understand the relationship between NH3 and meteorological parameters, correlation analyses were conducted for monthly average temperature (T) and total precipitation (P) in study area (p < 0.001=***, p < 0.01 =**, p < 0.05 =*). The results showed strong positive correlations between NH3 and T in both land types. In agricultural areas, the correlation was r = 0.93*** for Mersin, r = 0.87*** for Adana, and r = 0.96*** for Antalya. Over artificial surfaces, similarly strong correlations were observed: r = 0.93*** for Mersin, r = 0.93*** for Adana, and r = 0.96*** for Antalya. Further, NH3 and P was negatively correlated. In agricultural areas, the correlation was r = -0.91*** for Mersin, r = -0.84*** for Adana, and r = -0.86*** for Antalya. In artificial surfaces, the negative correlation remained strong: r = -0.92*** for Mersin, r =-0.84*** for Adana, and r = -0.87*** for Antalya. These negative correlations with P were likely mostly related to NH3 removal via wet deposition or impact on partitioning of NH3 in soil, while the strong positive correlations with T highlight the role of NH3 volatilization. In 2021, when large-scale wildfires occurred in Mersin, Antalya, and Mugla, NH3 concentrations during the defined fire period (28 July-7 August) were 94% higher than the pre-fire (18-27 July) period and 146% higher than the post-fire (08-17 August) period which this indicates an enhancement of NH3 related to BB. Then, subregions were selected for wildfire regions (WF) based on total grid-based FRP according to 2021 wildfire time interval. In the study area, 2 subregions for Antalya-AN (AN-1 and AN-2) and Mersin-ME (ME-1 and ME-2) and 4 subregions for Mugla (MU-1 to MU-4) selected. Based on the sub-regional analysis for the wildfire regions, NH3 enhancements were observed in all selected region especially in AN-1 and AN-2 regions which NH3 levels during the fire period increased by 308% and 594% compared to the pre-fire and post-fire periods, respectively. Similar patterns were also found in co-emitted pollutants, especially TROP-NO2 and TROP-HCHO, with increases exceeding 100% in most regions. For instance, in AN-1, NO2 rose by 77% (pre-fire) and 103% (post-fire), while HCHO increased by 105% and 128%. The enhancement ratios of NH3 to co-emitted pollutants during the fire period were notably higher than pre-fire and post-fire periods in most WF region, especially in AN-1, AN-2, and MU-3. For instance, in AN-1, the NH3/NO2 ratio increased from 7.51 (pre-fire) to 16.96 (fire), and in MU-3, it rose sharply from 11.08 to 56.04 which these results indicated a significant contribution of BB event to NH3 emissions relative to other pollutants. For NH3 to CO ratios, a similar pattern was observed. In AN-1, the NH3/IASI-CO ratio increased from 0.0041 to 0.0094, and the NH3/TROP-CO ratio increased from 0.0042 to 0.0104, which both doubled during the fire period. For the analysis of residue burning (RB) subregions were determined based on the cumulative grid-based FRP levels over a five-year period (2019-2023). Sub-regional analyses were conducted for Adana-Osmaniye (Ad-Os), Mersin-Adana (Me-Ad), and Hatay (Ha) with focused on two different fire-affected time intervals. For the Ad-Os region (RB-1), a longer fire period was defined from 15 August to 15 November 2020, with pre-fire and post-fire periods define as 5-14 August and 16-25 November 2020, respectively. For Me-Ad and Ha (RB-2), the fire period was defined as 15 August-30 September 2020, with pre-fire and post-fire periods define as 5-14 August and 1-10 October 2020, respectively. In Ad-Os region, noticeable NH3 increases were detected during the RB-1 fire period, with a 43% rise compared to the post-fire period. In Me-Ad, although overall enhancements were not as strong as in wildfire regions, NH3 increased by 20% during the RB-2 fire period compared to post-fire. In Ha region, NH3 showed a 56% increase from pre to fire RB-2 period which mostly Ha did not stand out in NH3 distribution. These increases highlight the importance of fire-related NH3 enhancements in local areas. These results indicated that even in the absence of intense wildfire activity, agricultural residue burning could elevate NH3 levels in the region. Further, when the impact of the 2021 wildfires on the marine environment was examined during the wildfire period, a significant increase in chlorophyll-a concentrations was observed in the downwind direction of the wildfire plume over the Mediterranean Sea. The maximum enhancement reached 553.6% from the pre-fire to fire period, with a mean increase of 98.5% and from the post-fire to fire period, the maximum increase was 568.9%, and the mean increase was 87.5%. These findings suggest that nitrogen deposition from wildfire smoke may have influenced phytoplankton growth in the Mediterranean. Further, the same analyses were conducted for the RB regions. However, unlike the WF regions, no clear increases were observed, except for localized enhancements along the coastal areas of the Me-Ad RB region. Overall, this thesis showed that BB-related NH3 enhancements are evident across the Eastern Mediterranean with co-emitted pollutants, especially during the 2021 wildfires. Moreover, the observed changes in chlorophyll-a concentrations highlight that large-scale BB events not only affect air quality but may also have broader environmental impacts through atmospheric deposition to the Mediterranean Sea