Project at a Glance

Title: Investigative modeling of PM2.5 episodes in the San Joaquin Valley Air Basin during recent years

Principal Investigator / Author(s): Kleeman, Michael

Contractor: UC Davis

Contract Number: 15-301

Research Program Area: Atmospheric Processes

Topic Areas: Chemistry & Reactivity, Modeling


The decreased severity of air pollution events in California over the last 15 years has benefited human health, yet also presented new challenges for air quality modeling. Chemical transport models (CTM) used in SIP development have not been able to completely adapt to the changing emissions and meteorological conditions. One of the results from this is that, compared with events 10-15 years ago, CTMs under predict peak nitrate concentrations in the San Joaquin Valley (SJV) by a much larger amount. To address this and other model shortcomings, this project addressed potential causes for under predictions in nitrate concentrations and, where possible, developed best available solutions. This work was carried out in two phases. An initial phase investigated possible modeling biases in both reactive nitrogen emissions and meteorological fields through various comparisons with measurements. Based on the results of this work, phase 2 investigated corrections to biases in emissions of nitrate precursors, corrections to biases in meteorological fields, optimization of nitrate production conditions, and refinements to the spatial resolution for nitrate formation. Using a revised CTM based on these findings, the Principal Investigator (PI) simulated several historical and current air pollution episodes and compared these with measurements from 2010 CalNex, 2013 DISCOVER-AQ, and CARB ground sites in 2015. In addition to improvements in descriptions of the meteorological fields, the PI proposed increases in nitrogen oxides (NOX) emissions, primarily from candidate soil emissions. Further work is needed to fully test this hypothesis and better understand the seasonal and agricultural impacts on this possible NOX source. Overall, the optimized CTM still has difficulties in the description of boundary layer dynamics and associated processes that recent work suggests is important in particulate nitrate formation in the SJV.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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