Isotopic Evidence for Changes in U.S. Energy Fuels and Impact on Particulate Nitrate

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Isotope Geochemistry

Background:

• The Clean Air Act reduced nitrogen oxide (NOx) emissions, decreasing acid rain but leaving particulate nitrate (pNO3) levels high.
• Linking NOx emission sources to pNO3 formation is challenging, hindering effective air quality control evaluations.
• Elevated pNO3 concentrations persist despite emission control efforts.

Purpose of the Study:

• To investigate the effectiveness of emission regulations on NOx sources using nitrogen isotopes.
• To understand the impact of changing NOx emission sources on particulate nitrate formation.
• To evaluate the success of past clean air policies for particulate air quality.

Main Methods:

• Analysis of nitrogen isotopes (δ15N) in particulate nitrate (pNO3).
• Utilized a 2005-2015 aerosol record from the northeastern U.S.
• Empirical confirmation of emission source contributions to pNO3.

Main Results:

• Nitrogen isotope data confirmed reduced coal-derived NOx emissions due to regulations.
• Observed an increasing influence of oil and natural gas combustion on NOx emissions.
• Demonstrated a direct link between emission source changes and pNO3.

Conclusions:

• Emission regulations have successfully altered NOx sources, reducing coal contributions.
• Understanding source-specific impacts on pNO3 is crucial for effective air quality management.
• Nitrogen isotope analysis provides a valuable tool for evaluating environmental policies.