UWFPS 2017 Scientific Questions and Deliverables

1. What is the spatial distribution, both vertically and horizontally, of key trace gases and aerosols related to PM formation? What are the limiting and excess reagents in ammonium nitrate formation, and what are the key source regions? What are the limiting and excess reagents in oxidant and nitric acid formation? Do these limitations and / or sources vary significantly across the region?

   Emissions within the three major valleys of the Wasatch Front are expected to be heterogeneous, with the largest urban emissions in the Salt Lake Valley and the largest agricultural emissions in the Cache Valley. Aircraft flights across all 3 valleys at different times of day will characterize the spatial distribution of NH3, HNO3 and NOx, together with the key intermediates in NOx oxidation. Comparison of these data to thermodynamic aerosol models will help to determine which reagents are limiting and where. Further, the aircraft measurements at different times of day will characterize transport of trace gases and aerosols, to assess the efficiency of residual layer transport in the distribution of pollutants and / or inter-valley coupling.

2. How do these distributions and the associated chemistry vary as a function of time of day? What are the most important chemical mechanisms for ammonium nitrate aerosol?

   Morning, afternoon and night flights will characterize the chemical and meteorological evolution of boundary layer breakup, re-establishment, and overnight residual layer chemistry and transport. Rates of chemical reactions may be a strong function of altitude at all times of day. Vertical profiles will probe this chemical composition for an integrated analysis of boundary layer structure and chemistry.

3. What is the role of the Great Salt Lake and Utah Lake, both chemically and meteorologically, in regional air quality? Are they significant sources of aerosolized chloride that perturbs nitrogen oxide chemistry? Do they play a role in transport and or storage of polluted air masses?

   Flights over large bodies of water at various altitude ranges should be feasible. These flights will characterize the vertical structure of winds over the lakes the transport pollutants, as well as the chemical composition at different altitudes.

4. Are there significant aerosol sources other than ammonium nitrate? What is the role of, for example, residential wood combustion as a source for organic aerosol?

   Deployment of the AMS will provide unprecedented detail in the measurement of organic aerosol composition to the northern Utah valleys. Furthermore, the iodide CIMS instrument will provide measurements of oxygenated organic and nitrogen containing compounds that are characteristic of residential wood combustion sources. The spatial distribution of these organic aerosol and oxygenated VOCs, together with the daily time evolution, will provide accurate data on the primary and secondary organic aerosol source from residential wood combustion.

5. What are the key emission sectors for aerosol precursors? What is the role of agricultural, industrial, urban, home heating, and natural emissions?

   Aircraft measurements can be compared to emissions inventories developed by UDAQ to assess the emission sources responsible for PM2.5. This comparison will benefit from local 3D air quality modeling capabilities of investigators in Utah, at the EPA or USDA, or at NOAA. Identification of a modeling component to this study will be a critical need going forward.