Environment and Ecology

Winner: Idalia Pérez, University of California, Berkeley
Calculations of the Chemical Composition of the Sacramento Urban Plume

Recent measurements within the Sacramento urban plume have provided a detailed benchmark for testing our understanding of tropospheric chemistry. Available measurements include a wide suite of VOC, NOy, O₃, and CO at the source and at a receptor site five hours downwind. Further, the meteorology in the region is extremely regular making it possible to evaluate effects of temperature or day-of-week patterns with a single season of measurements. Here we use a Lagrangian model representing transport from Granite Bay (GB), a suburb at the eastern edge of Sacramento, to the Blodgett Forest Research Station (BFRS). The model represents chemistry based on MCM v3.1 along with mixing and dilution. The model is initiated with concentrations of NOx, peroxynitrates, alkyl and multifunctional nitrates, HNO₃, VOCs and O₃ based on measurements at GB. BVOC emissions throughout the transect are included. The outputs of the model are compared with O₃ measurements at Cool 3 hours downwind, and detailed measurements of VOC, speciated nitrogen oxides and O₃ at BFRS, 5 hours downwind of GB. The comparisons indicate 1) O₃ at BFRS and Cool is largely driven by the combination of rural biogenic emissions and urban NOx emissions, 2) that OH is underestimated by standard chemical models, 3) that partitioning of NOy is dominated by peroxy and other multifunctional nitrates that are not represented in standard chemical models and which have a strong impact on how much NO2 is available for O₃ production.