Constraints on California and Arctic Methane Emissions Using a Regional Lagrangian Model and Aircraft-Based Measurements During the CalNex and HIPP O Campaigns

EPA Grant Number: FP917365
Title: Constraints on California and Arctic Methane Emissions Using a Regional Lagrangian Model and Aircraft-Based Measurements During the CalNex and HIPP O Campaigns
Investigators: Santoni, Gregory W
Institution: Harvard University
EPA Project Officer: Michaud, Jayne
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Fellowship - Global Change , Academic Fellowships


The California Global Warming Solutions Act (AB32, 2006) requires the state to cap its greenhouse gas emissions at 1990 levels by 2020, roughly 15 percent below current levels. Uncertainties in emission inventories, however, present a significant hurdle for the California Air Resources Board (CARB) in both setting and tracking progress toward greenhouse gas reduction goals. Current emissions inventories for methane (CH4), for instance, have never been validated at the regional scale and few data sources exist to characterize the effects of intensive agriculture in the Central Valley. Until CalNex-the Research at the Nexus of Climate Change and Air Quality campaign-no regional-scale observations were available to assess emissions inventories quantitatively. This study will address these limitations. Additionally, measurements taken during HIPPO (HIAPER Pole-to-Pole Observations) provide detailed distributions of CH4 over the arctic, useful in constraining the controls on CH4 fluxes in that region at seasonal timescales.


This study proposes generating reliable CH4 emissions over California, disaggregated spatially and by sector (agriculture, other land use, industry, transportation, etc.), by using the extensive set of airborne CH4 measurements acquired with the NOAA WP-3 aircraft during the CalNex campaign in conjunction with a regional-scale lagrangian particle dispersion model (LPDM). The Stochastic Time-Inverted Lagrangian Transport (STILT) model is an LPDM that can be used to estimate trace gas concentrations that correspond with individual measurements from an aircraft campaign or tower. STILT is particularly well-suited for estimating emissions because measured trace gas signals can be directly correlated back to specific upwind source locations. This study will use STILT along with high-resolution assimilated meteorological fields from the Weather Research and Forecasting (WRF) model and source a priori information to produce a “footprint”-a transfer function giving spatially and temporally resolved increments of CH4 mixing ratio in response to emission fluxes along the space/time trajectories. This will allow for the optimization of the a priori information to generate reliable CH4 emission inventories for California.

Expected Results:

This study will provide a robust constraint on baseline California CH4 emissions, allowing for further regulation, accountability of emissions and accurate tracking of progress towards achieving the goals put forth in AB32. This work also will improve understanding of the seasonality of arctic CH4 emissions and examine the effects global climate change will have on future emission rates.

Potential to Further Environmental/ Human Health Protection

CalNex provides an opportunity to produce reliable CH4 emissions constraints that will inform future state climate policy decisions. NOAA and CARB cite the improvement of emissions inventories as one of the key research objectives underlying the CalNex mission, and the study presented here will help achieve this goal. Given that methane has a relatively long residence time in the atmosphere, regional emissions have global consequences to the climate system and therefore understanding the controls on CH4 production and loss are essential in predicting future climate change.

Supplemental Keywords:

climate change, atmospheric chemistry, methane, Largrangian modeling, emission inventory, Arctic, California, Global Warming Solutions Act, AB32

Progress and Final Reports:

  • 2012
  • 2013
  • Final