The Northeast Corridor Urban Greenhouse Gas Project

As the population of cities grows globally due to trends toward urbanization, so does their relative contribution to global anthropogenic greenhouse gas (GHG) budgets. Increasingly, individual city and regional governments are making pledges to achieve ambitious GHG reduction targets. Atmospheric measurements provide additional useful information to such efforts, by confirming inventory estimates, detecting trends, or estimating emissions that are not well-quantified using inventory methods, such as methane and other non-CO₂ emissions.

Here we focus on the Northeast Corridor (NEC) project, whose objective is to isolate and quantify anthropogenic greenhouse gas (GHG) emissions from urban areas along the U.S. East Coast from many confounding sources upwind (cities, oil and gas development, coal mines, and powerplants) and from the large biological CO₂ signal from the highly productive agricultural areas and forests nearby and within the cities. The NEC project has a current focus on the urban areas of Washington, D.C. and Baltimore, Maryland, U.S.A., with existing plans to expand northward to cover the entire urbanized corridor of the Northeast U.S.

The NEC project includes multiple measurement and analysis components. The backbone of the NEC project is a network of in-situ CO₂ and CH₄ observation stations with continuous high-accuracy mole fraction measurements of these two greenhouse gases. In addition, periodic flight campaigns of multiple weeks each year are conducted by the University of Maryland and Purdue University, focusing on wintertime observations of CO₂, CH₄, and CO from instrumented aircraft. The NEC project also includes an extensive modeling component, using high-resolution meteorological model output from the Weather Research and Forecasting (WRF) model coupled to Lagrangian dispersion models (e.g. STILT or NOAA’s HYSPLIT) to interpret observations from both aircraft and tower stations and in atmospheric inverse analyses to estimate fluxes of CO₂ and CH₄ from the Northeast U.S, focusing on Washington D.C. and Baltimore, MD.

We will present recent modeling work from the NEC project for a one-year period (November 2016 – November 2017). Using a WRF-STILT modeling framework we evaluate biospheric CO₂ fluxes and modeled background CO₂ for a regional domain stretching from Iowa to the East Coast of the U.S. We also use the same framework to evaluate different existing gridded methane inventories over the same domain, which includes oil and gas production regions, coal extraction operations, and all the urban centers from Richmond, VA to Boston, MA. For both of these efforts (CO₂ and CH₄), we compare modeled concentrations to observations at 29 tower locations in the domain. We also compare against flight observations from NASA’s ACT-America project in 2017. Finally, we will present the atmospheric flux inversion framework to be employed in flux estimation over the larger domain described above (0.1 degree) as well as a high-resolution (0.01 degree) domain over Washington D.C. and Baltimore, MD, including methodology for estimating the background concentrations of CO₂ to be used to derive enhancements at the urban towers.