Airborne Laboratory for Atmospheric Research

We have developed the capability to routinely measure the fluxes of greenhouse gases using ALAR, an instrumented Beechcraft BE76 Duchess aircraft (top left picture). We focus on quantifying emissions of carbon dioxide (CO₂) and methane (CH₄) from urban areas and point sources, such as power plants, landfills, and natural gas drilling and holding sites. A Picarro cavity ring-down spectrometer (CRDS; bottom left picture) has permanent residence behind the ALAR's pilot seat for measurements of CO₂, CH₄, and H₂O. The rear two seats of the aircraft have been removed to accommodate the installation of other instruments which we rotate depending on our science questions. 

 

Real-time (50Hz) vertical wind data is measured using the BAT probe developed by Crawford et al., Bound. Lay. Meteor, 1992.  The vertical wind data is complemented by aircraft altitude measurements using an inertial navigation system and Global Positioning System.  A set of wind tunnel and in-flight experiments were used to calibrate and characterize the vertical wind system to minimize systematic errors caused by airflow measurements that depart from a commonly used theoretical potential flow model.  The results of these vertical wind studies are published in Garman et al., J. Atmos. Ocean. Tech., 2006.

 

Current Projects:

The INdianapolis FLUX Experiment (INFLUX)

Quantifying greenhouse gas (GHG) emissions from Indianapolis is an ongoing project in our group, part of the Indianapolis Flux Experiment (INFLUX), that we created. INFLUX is a multi-institutional collaborative effort aimed at developing, improving and evaluating techniques to quantify GHG emissions. Because cities are major GHG sources, future attempts at carbon mitigation strategies will likely rely on GHG reduction from cities.  This will require the ability to quantify and verify emission reductions.

As air flows across urban areas, it picks up CO₂ and CH₄ emissions from point sources such as power plants, cars, and natural gas leaks, as depicted in the schematic below (left).  Flying downwind of the city at multiple altitudes and perpendicular to the prevailing wind direction produces a picture of the urban CO₂ and CH₄ plume. Using this airborne mass-balance approach (urban enhancement = downwind-background) we can calculate the emission rate of GHG's from urban areas. We show an example mass balance flight path below on the right.

  

 

The Northeast Corridor

We have been working with the National Institute of Standards and Technology (NIST) and the University of Maryland (UMD) to also focus on the northeast corridor urban areas, primarily Washington, D.C., Baltimore, and more recently New York City.  This has included many mass balance flights, many of which make use of both UMD and Purdue aircraft to more thoroughly understand emissions.  Most recently our work has involved using modeling to better understand emissions in New York City and how our measurements compare to inventory estimates, as shown below for one of the inventories tested.

Power Plant Pseudo-Controlled Release

ALAR has completed many mass balance experiments downwind of power plants to investigate the potential CH₄ emissions.  However, power plants are required to measure their CO₂ emissions using Continuous Emissions Monitoring Systems (CEMS) and report them to the air market program data.  This provides us with the opportunity to test our GHG quantification methodology.  We use this dataset of over 50 mass balance experiments downwind of power plants to compare directly to these reported emissions and assess our technique's bias and uncertainties.

Modeling Turbulence in NYC

Part of quantifying GHG emissions from cities requires accurate model depictions of the airflow in and around those cities. Cities present a rough surface, often rougher than the natural environment, that can create eddies in the atmosphere which affect mixing and vertical motion, and thus GHG dispersion. Turbulent kinetic energy (TKE) is a measure of this turbulence in the atmosphere.

Our group takes high-frequency wind data from ALAR's BAT probe to quantify the TKE around New York City, (example flight on left,) then simulates the atmosphere on those days in the Weather Research and Forecasting (WRF) model to see how well the model simulates the observed TKE. We find that WRF generally underestimates TKE directly downwind of the major skyscrapers in Manhattan (curtain plots below) using several of the different schemes available in WRF for modeling the atmospheric boundary layer.

Highlights from past ALAR projects:

• Quantification of emissions from the northeast corridor:
  • Trend analysis of and COVID impact on CO emissions from DC-Baltimore: Lopez-Coto et al., 2022, ES&T
  • Inverse modeling of New York City CO₂ and CH₄ emissions: Pitt et al., 2022, Elementa
  • Relative emissions of biogenic and natural gas-derived methane from 7 cities: Floerchinger et al., 2021, Elementa
  • Quantifying CO₂, CH₄, and CO from DC-Baltimore via inversion: Lopez-Coto et al., 2020, ES&T
  • Quantifying CH4 from DC-Baltimore via MBE and comparison to inventories: Ren et al., 2018, JGR: Atmospheres
  • Quantifying NOx and CO from DC-Baltimore: Salmon et al., 2018, ACP
• Chemical Imaging of aerosol collected over crop fields: Tomlin et al., 2020, ACS Earth Space Chem.
• Urban water vapor and its vertical distribution:
  • Isotopic study of the vertical distribution of water vapor: Salmon et al., 2019, ACP
  • Urban emissions of water vapor downwind of Indianapolis and DC-Baltimore: Salmon et al., 2017, JGR: Atmospheres
• Quantifying emissions from power plants:
  • Followup study with a much larger number of facilities: Hajny et al., 2019, ES&T
  • Initial study of natural gas-fired power plants and oil refineries: Lavoie et al., 2017, ES&T
• Particle number concentration over the Great Lakes
  • Lake spray aerosol's affect on clouds: Olson et al., 2019, ACS Earth Space Chem.
  • Aerosol production from the surface of the great lakes: Slade et al., 2010, GRL. 
• INFLUX papers:
  • Improving the precision of the airborne mass balance experiment: Heimburger et al., 2017, Elementa
  • CH₄ emissions from landfills: Cambaliza et al., 2017, Elementa
  • Quantifying and partitioning Indianapolis CH₄ emissions: Cambaliza et al., 2015, Elementa
  • Assessing the uncertainties of the aircraft mass balance approach: Cambaliza et al., 2014, ACP
  • Our first Indianapolis emissions paper!: Mays et al., 2009, ES&T
• Quantifying emissions from an urban Indiana landfill: Cambaliza et al., 2017, ES&T
• AirMOSS - Forest CO₂ exchange using airborne eddy covariance
• Quantifying emissions from shale formations:
  • Spatiotemporal variability of CH₄ emissions from the Eagle Ford Basin: Lavoie et al., 2017, ES&T
  • Barnett Shale emissions: Lavoie et al., 2015, ES&T
  • Marcellus Shale emissions: Caulton et al., 2014, PNAS
  • Flaring efficiency: Caulton et al., 2014, ES&T
• Regional CO₂ surface fluxes: Martins et al., 2009, Agr. Forest Meteorol.
• Vertical winds correction due to aircraft lift-induced upwash: Garman et al. 2008, Bound. Lay. Meteorol.