Interpreting greenhouse gas and air pollution surface measurements to quantify urban emissions

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Quantifying and monitoring urban emissions of greenhouse gases (e.g., carbon dioxide, methane, nitrous oxide) and air pollutants (e.g., carbon monoxide, NOx, ozone, aerosols) is crucial for verifying that emission reduction targets are met and that our air quality remains at safe levels. To quantify urban emissions directly from atmospheric measurements, we require precise and accurate measurements of atmospheric gas mixing ratios and the height of the atmosphere into which they mix. This proposal seeks funds to purchase a micro-pulse LIDAR: an instrument that will measure the atmospheric mixing height. To date, our interpretations of the existing mixing ratio measurements and our ability to produce accurate emission values in Toronto has been limited by uncertainties in the mixing height over the city. The mixing height changes between night and day, summer and winter, and with changing weather. An additional complication for urban studies is the influence of the urban form on the mixing height, creating an “urban dome” with a higher mixing height than the surrounding area. Thus, the requested instrument is a time-resolved, robust, portable, state-of-the-art system. It will be be stationed on the McLennan Physical Laboratories rooftop at the University of Toronto for continuous side-by-side measurements with existing trace gas and aerosol measurements, will be periodically moved throughout Toronto to characterize mixing heights at other observing stations, and driven across the city to accurately define Toronto's urban dome. There is no existing instrumentation in the greater Toronto area that makes portable mixing layer height measurements, and thus these measurements will create a unique and highly valuable dataset for those interested in studying Toronto’s urban emissions.