O3-NOx-VOC sensitivity and NOx-VOC indicators in Paris: Results from models and Atmospheric Pollution Over the Paris Area (ESQUIF) measurements

[1] A three-dimensional photochemical model has been used to interpret aircraft measurements from the Atmospheric Pollution Over the Paris Area campaign near Paris, with special attention to measurements that are related to predicted O3-NOx-volatile organic compound (VOC) sensitivity. The model (CHIMERE) includes a representation of ozone formation over Europe and a more detailed spatial representation of the region around Paris. A series of model scenarios were developed with varying wind speeds and emission rates. Comparisons are shown with measured O3, total reactive nitrogen (NOy), summed VOCs, and isoprene. Results show that model NOx-VOC sensitivity predictions are correlated with the ratio O3/NOy but not with O3/peroxyacetyl nitrate. Measured O3 and NOy on high-ozone days tends to agree with model values when models predict NOx-sensitive or transitional chemistry but not when models predict VOCsensitive chemistry. Model values for O3/NOy and the O3-NOy slope are lower than measured values, suggesting the possibility of missing, unmeasured VOCs in the Paris plume. Standard performance tests for ozone models, such as normalized bias, show good agreement between models and measurements, even in cases when significant differences appear in the O3-NOy correlation. Model predictions shift slightly toward NOx-sensitive chemistry when model wind speeds are increased. Isoprene represents 20% of total VOC reactivity–weighted carbon in the center of the Paris plume and 50% in the surrounding rural area during high-ozone events.