Impact/Purpose:

Our objectives are to use tall tower micrometeorological flux measurements of air pollutants in an urban area to derive direct information on emissions sources, which commonly are only indirectly inferred from ambient measurements and extrapolations from data obtained under controlled conditions. We hypothesize that our data from this typical urban region of Houston, Texas, can be used to identify inaccuracies in and adjust current emissions inventories, and can inform emissions on larger scales creating improved inventories that lead to improved air quality modeling.

Description:

This project uses a novel approach to measure real-world pollutant fluxes on an extended spatial and temporal scale, and to infer from those the source-specific pollutant emissions needed for a comparison to and an improvement of current emissions inventories. Air pollutants addressed include EPA criteria pollutants except SO2 and Pb, and volatile organics that are either air toxics (e.g. benzene) and/or photochemical ozone formation precursors (e.g. isoprene). We will:

• commence and extend our micrometeorological measurements of pollutant fluxes in urban Houston, Texas, for two years,
• compare measured to modeled fluxes in a top-down-bottom-up approach, and
• use the comparison to adjust the inventory and test its effects on air quality modeling.

Analyses will use existing and newly acquired air pollutant data, particularly flux data, geographic information systems, and modern statistical methods to study typical and extraordinary emission situations, then compare mapped emissions with expected emissions. Ultimately, identified shortcomings in expected emissions will be used to update emission inventories used in current air quality modeling to study whether the modifications improve forecasts.

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The experimental approach uses well-established micrometeorological methods to measure fluxes, and novel means, such as flux footprint analysis, positive matrix factorization, and advanced air quality modeling, to analyze the results. Volatile organic compound (VOC) fluxes are measured with a relaxed eddy accumulation (REA) GC-FID method, criteria air pollutant (CO, NOx, and O3) fluxes are assessed with a flux gradient method. Particulate Matter (PM) number density fluxes will be measured with a novel REA method. Measured fluxes (top-down) will be compared to expected fluxes using footprint modeling by overlaying the footprint density function with various GIS data sets upgraded by onsite surveys. Detailed traffic surveys will be conducted as input, particularly into MOBILE6 and the new MOVES model to create bottom-up estimates of pollutant emissions from roads in the tower’s flux footprint. Additional ground surveys (land use) are conducted to inform an evaporative (organics) and mechanical (PM) sources geographic information system to assess non-road emissions. Top-down-bottom-up comparisons will be used to inform necessary changes to the inventory, which will be applied to larger areas for selected air pollution episodes to compare detailed CMAQ air quality modeling outputs using altered inventory input.

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