Sensitivity of photochemical pollution using the adjoint of a simplified chemistry-transport model

The nature of two summertime photooxidant pollution episodes over Paris is investigated by means of adjoint modeling. The first episode (July 12, 1994 ) is characteristic of a 'local production' episode, while the second (Augu st 12, 1997) is mostly due to advection into the urban area of high concent rations of ozone. We calculate the sensitivities to emissions of individual primary species and to reaction rate coefficients using the adjoint of a s implified multibox model representing the urban and suburban areas of thf c ity of Paris. Sensitivity to emissions demonstrates that the first episode is essentially sensitive to volatile organic compounds (VOC)/NOx emissions, while the second is sensitive. to NOx, emissions. These results also point out, the two important emission activity categories: traffic and solvent u se, the second one being more sensitive than the first one. Sensitivity to reaction rates indicates that oxidant production is only sensitive to a. fe w reactions. The high sensitivity of photochemical pollutants peaks to part icular chemical reactions points out the necessity to refine the knowledge of their reaction rates.