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Project Status: complete

Title: Ozone in the Lower Atmosphere and its contribution to high ozone concentrations at ground-level in the Southern San Joaquin Valley

Principal Investigator / Author(s): Faloona, Ian

Contractor: UC Davis

Contract Number: 14-308


Research Program Area: Atmospheric Processes, Emissions Monitoring & Control

Topic Areas: Field Studies, Modeling, Monitoring


Abstract:

We collected an unprecedented airborne data set by extensively sampling the lower 1500m (~5,000 ft.) of the atmosphere in the Southern San Joaquin Valley (SSJV) in order to characterize conditions aloft to help improve the state's ability to model/predict surface ozone concentrations. Sampling occurred nearly all the way to the surface at four local airports and throughout the entire day/night cycle. Data were collected spanning five different, continuous 2-6 day periods during the summer when ozone air pollution is at its worst. The project utilized a well-instrumented scientific research aircraft operated by Scientific Aviation, Inc. to measure winds, temperature, humidity, ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), and methane (CH4).

The experimental design further provided for an empirical estimation of the overnight vertical mixing strength between the layer aloft and the shallow nocturnal boundary layer. Similarly, midday entrainment rates of air aloft mixing into the valley boundary layer were quantified, which is a critical parameter in controlling ventilation of surface air in the valley. Regional emission rates of methane and NOx were estimated to be substantially larger than current inventories suggest. Finally, the midday photochemical production rate of ozone was estimated and seen to correlate with day-to-day variations in the observed NOx concentrations indicating that the southern San Joaquin Valley is predominantly NOxlimited with respect to local ozone production. Preliminary analyses of these airborne and surface wind profiler data at Visalia indicate that overnight mixing is strongly influenced by the strength of the nocturnal jet (the up-valley wind associated with the so-called 'Fresno Eddy') and that a stronger jet results in more nighttime ozone loss at the surface, which impacts the following afternoon's peak ozone levels. Finally, the net chemical loss of ozone overnight from the production of nitrate is not well understood and further study of the fate of the nitrate radical is needed to better quantify this important loss in air quality models.


 

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 322-3893

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