The Megacities Carbon Project is developing and testing methods for monitoring the greenhouse gas emissions of cities, the largest human contributors to climate change. Observations of the concentrations of carbon dioxide (CO2), methane, and other gases in the atmosphere can be used to estimate the locations and strengths of different emission sources. Interpreting measurements of gas concentrations at one location to infer an emission source at another location is complicated by the effects of the Earth's atmosphere which is always in motion. For example, increasing concentrations of CO2 at a given location can either be due to increasing emissions or stagnant or sinking air whereas decreasing concentrations of CO2 can either be due to decreasing emissions or strong winds or rising air.
This visualization shows the output of a high-resolution model of the atmosphere over Los Angeles (courtesy Meemong Lee and Zhijin Li, NASA/JPL). The model is based on meteorological measurements for one month in the spring of 2010 at a resolution of 1 km and 3 hours. Vertical motion of the Earth's Planetary Boundary Layer (PBL) - the lowest part of the atmosphere that hugs the surface of the Earth - is represented by the gray "blanket". The height of the PBL is largely driven by convection associated with the changing surface temperature of the Earth (for example, rising during the day and sinking at night). The colored arrows represent the strength and direction of winds at different altitudes. The Megacities Carbon Project includes measurements and models of PBL dynamics and winds to help interpret measurements of greenhouse gas abundances at different locations around the basin. Measurement systems include wind speed and direction indicators and laser detection and ranging (lidar) instruments to track the changing PBL height.