While much attention has been drawn to daytime oxidation of biogenic VOCs, the nighttime chemical and physical processes remain largely uncertain. In particular, their impacts on daytime ozone are poorly understood. Here we use a high resolution global chemistry-climate atmosphere model (GFDL AM3), to evaluate nighttime observations collected from the recent NOAA SENEX aircraft campaign (June 1st to July 15th 2013). Model results are evaluated with nighttime observations of NO3, N2O5, isoprene, monoterpenes, oxygenated VOCs and reactive nitrogen species. Remarkably both measurements and model show a large amount of oxygenated VOCs in the residual layer after sunset, providing important precursors for nighttime chemistry in this layer. Measurements also suggest that a major fraction of power plant NOx was in fact injected into the residual layer. We show from model results that injecting nighttime NOx plumes in residual layer instead of surface layer has a significant impact on afternoon surface ozone. This is in part due to active nighttime chemistry in the residual layer that acts as an efficient sink for nighttime NOx, and in part due to the segregation of the residual layer from surface layer that prevents nighttime NOx from contributing to daytime ozone production in the surface layer. Our results suggest that accurate representation of nighttime chemical and physical processes in the model are critical for predicting daytime afternoon. We will also discuss the implications of these nighttime processes on the export of NOx from continental boundary layer.

How does nighttime oxidation of biogenic VOCs impact daytime ozone?

249th National Meeting (2015)

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