About Atmospheric Chemistry, Carbon Cycle, & Climate (AC4)

Program goal: Determine the processes governing atmospheric concentrations of greenhouse gases and aerosols in the context of the Earth System and Climate.

AC4 is a competitive research program formed in Fiscal Year 2013 that incorporates research on atmospheric chemistry and carbon cycle. The program aims to provide a process-level understanding of the climate system through observation, modeling, analysis, and field studies to support the development and improvement of models and ultimately predictions. In collaboration with NOAA Laboratories and academic community, AC4 program supports research on chemically active greenhouse gases, aerosols, their precursors, aerosol-cloud interactions in connection with field studies, as well as research on atmospheric components of carbon cycle and nitrogen cycle. 

Current AC4 research priorities are: 

1. Observational constraints on sources and sinks of greenhouse gases and aerosols

Accurate estimates of greenhouse gas and aerosols, including precursor emissions are at the core of climate forcing calculations. Accurate estimates of deposition and understanding of deposition processes is the complementary component to understanding the atmospheric budget. Both anthropogenic and natural flux estimates, however, remain very uncertain. Terrestrial emission estimates, particularly of biogenic aerosol precursors and of agricultural ammonia, nitrous oxide, and methane, represent a gap in knowledge, and they would benefit from additional observations and from analysis of recent and future NOAA field measurements (e.g., CalNex, SENEX). AC4 supports research on quantifying emission and deposition of greenhouse gases and aerosols in largely in connection with NOAA data. 

Emissions from megacities and other metropolitan areas, both in the U.S. and abroad, are projected to grow in coming decades, and their estimates require targeted measurements (such as CalNex and INFLUX) and analysis of multi-species and/or isotopic data sets. AC4 supports research on quantifying carbon fluxes within urban domes. 

Meanwhile, oil prices and recent technology improvements have led to an explosion of oil & gas extraction in the US. Emissions from oil & gas extraction have severe air quality and climate consequences. The leading source of methane in the US is now oil & gas industry. Atmospheric impacts of oil & gas extractions include leakage of methane and emissions of ozone precursors and aerosols. AC4 efforts complement those of scientists from NOAA/ESRL Chemical Science Division and Global Monitoring Division, and include measurements of emissions from a number of source regions across the Nation.

Policy makers, industry, scientists, and the public need accurate carbon dioxide flux information to make informed decisions related to atmospheric greenhouse gas levels. NOAA/ESRL/GMD’s CarbonTracker, a system that produces quantitative estimates of atmospheric carbon uptake and release for North America and the rest of the world that are consistent with observed patterns of CO2 in the atmosphere, is designed to supply that information. The new release of CarbonTracker ("CT2013") uses multiple models to explicitly estimate the influence of first-guess fluxes on the final result. CarbonTracker is intended to be a tool for the community, and feedback and collaboration from anyone interested are welcome.    AC4 efforts complement those of scientists from NOAA/ESRL Global Monitoring Division by supporting extramural scientists focused on various improvements to CarbonTracker.

2. Improved understanding of nitrogen cycle

Human activities have vastly perturbed the nitrogen cycle, which has resulted in emissions and deposition of climate-relevant atmospheric constituents. While N2O is a major greenhouse gas and ozone-depleting substance, other nitrogen containing species contribute to ozone production and aerosol formation, with a resulting mix of uncertain positive and negative radiative forcing. Extensive measurements have been made of various nitrogen-containing species (e.g., SOS99, CalNex, NACHTT), including aerosols and aerosol precursors.  

3. (EMERGING) Atmospheric composition from space

An emerging focus for AC4 is a collaboration with NOAA's Joint Polar Satellite System (JPSS). Starting with a workshop focused on current and potential future community needs and opportunities for data from CrIS instrument, AC4 will enhance its scientific focus by also developing, validating and applying atmospheric composition products retrieved from CrIS.




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