Modeling efforts will first develop a spatial distribution of expected methane and ethane emissions from different sources for the Houston region. Ethane is considered because it is co-emitted with methane from natural gas sources but not from landfills, wastewater treatment plants, and natural sources of methane (e.g., wetlands). Natural gas processing facilities and petrochemical plants report their emissions to the US EPA, and the routes of major transmission pipelines are available in geographic information systems. Because detailed characteristics of local natural gas distribution infrastructure are unavailable, we will use data on neighborhood age, housing density, and other features to map the expected spatial distribution of methane emissions from the local gas distribution system in the Houston area.
The Community Multiscale Air Quality (CMAQ) model will then be used to simulate the expected distribution of methane and ethane in the Houston region. CMAQ does not currently simulate variations in methane levels. Thus, we will modify CMAQ to simulate methane explicitly, expanding the model's capabilities for future studies to better characterize this important greenhouse gas and precursor of ozone pollution. Comparisons of modeled and measured levels of the gases will help identify potential discrepancies between the emission inventory and actual emission rates.