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A study on ammonia and fine particle formation in agricultural environments

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Author(s)
김준우
Type
Thesis
Degree
Doctor
Department
대학원 환경에너지공학부
Advisor
Park, Kihong
Abstract
Studies on fine particle formation and precursors have largely focused on urban areas. However, global agricultural production has grown significantly, leading to increased emissions and ambient concentrations of ammonia (NH3). Despite recent efforts to reduce urban emissions, fine particle nitrate levels affected by NH3 have not decreased in Northeast Asia. Additionally, crop residue open burning remains prevalent, contributing to fine particle levels. This underscores the need for further studies on NH3 and fine particle formation in agricultural environments. Livestock waste is the dominant source of agricultural NH3 emissions (e.g., about 90% in South Korea). Previous studies in South Korea estimated NH3 emission factors from livestock waste using flux chambers and indoor measurements. However, these methods do not account for meteorological influences and are prone to underestimation. Ambient downwind measurements combined with inverse modeling, which incorporate meteorological influences, have yet to be applied in South Korea. Atmospheric composition in Northeast Asia changes in a complex way with nitrogen oxides (NOx) decreasing and ozone (O3) increasing. NH3 and fine particle nitrate levels vary by location, either remaining stable or increasing. Fine particle nitrate levels are notably high, even in summer. However, summer nitrate formation remains unclear without a detailed discussion of nitric acid-nitrate partitioning and nitric acid production processes. This also complicates decisions on which emissions should be prioritized for reduction. Biomass burning, including crop residue open burning, is known to affect fine particle levels through primary emissions near the source as well as secondary products in downwind areas. Previous studies demonstrated the rapid evolution of emissions, including gas-phase oxidation and secondary organic aerosol (SOA) formation. However, onsite surface photochemical activity and SOA species have rarely been reported, potentially underestimating the full impact of biomass burning emissions. This PhD dissertation aims to: (1) estimate NH3 emissions from an intensive livestock farming area using inverse modeling, (2) understand nitrate formation through partitioning and production processes at agricultural sites, and (3) identify onsite surface photochemical activity and SOA compounds during a biomass burning event. Field measurements of gases and fine particle properties were conducted at a livestock site in summer and winter, and at a cropland site in summer in Gimje, South Korea. Key measurements included stationary and mobile NH3 instruments, multi-axis differential optical absorption spectroscopy (MAX-DOAS), and negative-mode electrospray ionization-Fourier transform-ion cyclotron resonance-mass spectrometry ((–)ESI-FT-ICR-MS). Applied models included the WindTrax backward Lagrangian stochastic model for estimating NH3 emissions, the E-AIM thermodynamic equilibrium model for analyzing NH3 and nitric acid-nitrate partitioning, and the RAPSODI algorithm for retrieving vertical gas concentration profiles following MAX-DOAS spectral evaluation. NH3 emissions from pig waste in an intensive livestock farming area in South Korea were estimated using inverse modeling for the first time, revealing values 7% and 46% higher than those obtained from flux chambers and indoor measurements, respectively. This study highlights significant differences in NH3 emission estimates depending on methods used. Inverse modeling, alongside flux chambers and indoor measurements, could provide a more balanced refinement of livestock NH3 emission factors in South Korea. Fine particle nitrate concentrations at agricultural sites in summer were elevated by high NH3 levels, which increased the particle-phase nitrate fraction, and were little affected by low NOx levels, because nitric acid was produced under high-NOx conditions. This underscores the varying impacts of changes in different precursor species on summer nitrate formation. Controlling summer nitrate concentrations can be achieved by reducing moderate NH3 emissions (excluding NH3 hotspots) and significantly cutting NOx emissions. During a summer crop residue open burning event, significant enhancements in surface photochemical activity (hydroxyl radical production) and SOA compounds, such as nitrooxy- organo-sulfates and nitro-catechols, were identified. This highlights that, in addition to primary emissions, strong onsite SOA formation can significantly contribute to onsite fine particle levels. Reducing crop residue open burning practices could mitigate fine particle events more effectively than previously understood.
URI
https://scholar.gist.ac.kr/handle/local/18912
Fulltext
http://gist.dcollection.net/common/orgView/200000827016
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