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The formation of inorganic fine particulate matter (i.e., iPM2.5) is controlled by the thermodynamic equilibrium partitioning of NH3-NH4+. To develop effective control strategies of PM2.5, we aim to understand the impacts of changes in different precursor gases on iPM2.5 concentrations and partitioning of NH3-NH4+. To understand partitioning of NH3-NH4+ in the southeastern U.S., responses of iPM2.5 to precursor gases in four seasons were investigated using field measurements of iPM2.5, precursor gases, and meteorological conditions. The ISORROPIA II model was used to examine the effects of changes in total ammonia (gas + aerosol), total sulfuric acid (aerosol), and total nitric acid (gas + aerosol) on iPM2.5 concentrations and partitioning of NH3-NH4+. The results indicate that reduction in total H2SO4 is more effective than reduction in total HNO3 and total NH3 to reduce iPM2.5 especially under NH3-rich condition. The reduction in total H2SO4 may change partitioning of NH3-NH4+ towards gas-phase and may also lead to an increase in NO3− under NH3-rich conditions, which does not necessarily lead to full neutralization of acidic gases (pH < 7). Thus, future reduction in iPM2.5 may necessitate the coordinated reduction in both H2SO4 and HNO3 in the southeastern U.S. It is also found that the response of iPM2.5 to the change in total H2SO4 is more sensitive in summer than winter due to the dominance of SO42− salts in iPM2.5 and the high temperature in summer. The NH3 emissions from Animal Feeding Operations (AFOs) at an agricultural rural site (YRK) had great impacts on partitioning of NH3-NH4+. The Multiple Linear Regression (MLR) model revealed a strong positive correlation between cation-NH4+ and anions-SO42− and NO3−. This research provides an insight into iPM2.5 formation mechanism for the advancement of PM2.5 control and regulation in the southeastern U.S.
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Chemical Speciation: Defining the Niche of Hot Spring Ammonia-Oxidizing Archaea (Oral Presentation)
The availability of chemical energy supplies is fundamental to environmental and planetary habitability. However, the presence of a chemical energy supply does not guarantee the presence of microorganisms capable of consuming it. In this study, chemical energy supplies available in Yellowstone National Park (YNP) hot springs were calculated, and the results indicate that ammonia oxidation, calculated using total dissolved ammonia, is one of the major energy supplies. Nevertheless, known ammonia-oxidizers (AO) are only present in a small fraction of the hot springs tested. Where AO are present, they do not dominate the microbial communities (relative abundances <5%), even in cases where total dissolved ammonia oxidation is the richest energy supply. The AO in YNP hot springs are predominantly ammonia-oxidizing archaea (AOA), which tend to favor environments with low total ammonia (sum of NH3 and NH4+) concentrations, despite the requirement of ammonia (NH3) as a substrate. Hot spring pH and temperature determine the ratio of NH3 to NH4+ and, consequently, NH3 availability to resident AOA. In this study, total ammonia measurements were collected from YNP hot spring samples using ion chromatography in coordination with biological sampling. DNA was extracted from simultaneously collected samples for 16S rRNA gene sequencing and analysis, and for the identification of known AOA. The WORM-portal (https://worm-portal.asu.edu/) was used to speciate the total ammonia measurements into ammonia and ammonium activities. By performing speciation calculations, we identified a potential lower limit for substrate (NH3) availability and a potential upper limit for NH4+ concentrations for the YNP hot spring AOA. Thus, the niche for AOA across YNP hot springs is dictated by the form of the total dissolved ammonia present, not by the energy supply available for total dissolved ammonia oxidation.
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- Award ID(s):
- 2327807
- PAR ID:
- 10630500
- Publisher / Repository:
- Goldschmidt 2025 Conference
- Date Published:
- Format(s):
- Medium: X
- Location:
- Goldschmidt 2025, Prague, Czech Republic
- Sponsoring Org:
- National Science Foundation
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Soil ammonia (NH3) emissions are seldom included in ecosystem nutrient budgets; however, they may represent substantial pathways for ecosystem nitrogen (N) loss, especially in arid regions where hydrologic N losses are comparatively small. To characterize how multiple factors affect soil NH3 emissions, we measured NH3 losses from 6 dryland sites along a gradient in soil pH, atmospheric N deposition, and rainfall. We also enriched soils with ammonium (NH4+), to determine whether N availability would limit emissions, and measured NH3 emissions with passive samplers in soil chambers following experimental wetting. Because the volatilization of NH3 is sensitive to pH, we hypothesized that NH3 emissions would be higher in more alkaline soils and that they would increase with increasing NH4+ availability. Consistent with this hypothesis, average soil NH3 emissions were positively correlated with average site pH (R2 = 0.88, P = 0.004), ranging between 0.77 ± 0.81 µg N-NH3 m−2 h−1 at the least arid and most acidic site and 24.2 ± 16.0 µg N-NH3 m−2 h−1 at the most arid and alkaline site. Wetting soils while simultaneously adding NH4+ increased NH3 emissions from alkaline and moderately acidic soils (F1,35 = 14.7, P < 0.001), suggesting that high N availability can stimulate NH3 emissions even when pH is less than optimal for NH3 volatilization. Thus, both pH and N availability act as proximate controls over NH3 emissions suggesting that these N losses may limit how much N accumulates in arid ecosystems.more » « less
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