Monitoring methane in the northeastern US using a network of instruments at tall towers

Methane is one of the major greenhouse gases and in recent years more efforts have been undertaken to estimate its emissions at local and regional scales utilizing new observing systems. During 2012, Earth Networks Inc. deployed a dense GHG observing network in mid-Atlantic region installing cavity ring-down spectrometers (CRDS) continuously measuring at tall towers. Every site has a collocated weather station providing real-time wind, temperature, humidity, pressure and other atmospheric parameters. Additionally, there are surface weather stations in the area surrounding the towers. In this study we use atmospheric observations provided by the GHG and weather networks to analyze spatial distribution of methane and to detect its sources in the northeastern US. We analyze the data from five sites in the region where there is an ongoing hydraulic fracturing (“fracking”), and identify the spikes in the observations when winds are from that area. Measurements of GHG's are taken at two heights allowing for identification of periods when boundary layer is well mixed and periods when nearby sources significantly impact methane readings. We also use the WRF model to compare simulated dispersion patterns with observed mixing ratio. Combining atmospheric observations with prior emission estimates from inventories and computing footprints using a coupled WRF-STILT system, we carry out the inversions and estimate the uncertainties. Transport model fields from WRF, including boundary layer heights, are validated on Earth Networks' weather observations as well as radiometers and profilers data.