Ozone response to precursor controls in very complex terrains: Use of photochemical indicators to assess O₃‐NOx‐VOC sensitivity in the northeastern Iberian Peninsula

The kinetics of ozone (O 3 ) chemistry and its two main precursors, nitrogen oxides (NO x ) and volatile organic compounds (VOC), represents an important field of uncertainty in atmospheric chemistry and photochemical modeling. This uncertainty affects the design of control strategies to reduce tropospheric O 3 production. The effect of controlling ozone precursors on sensitivity regimes was evaluated by performing simulations with MM5‐EMICAT2000‐CMAQ model to represent O 3 formation in the northeastern Iberian Peninsula with baseline emission rates for VOC and NO x , and reducing anthropogenic VOC and NO x emissions on a 35%. Three different scenarios were considered in order to assess chemical sensitivity in urban, industrial, and background domains. Areas downwind of the city of Barcelona benefit from NO x reductions (reduction of 10 ppb in ground‐level O 3 ), while the same reduction causes an important increment of O 3 in Barcelona (9 ppb) and the area downwind of Tarragona (18 ppb), with a high industrial influence. The city of Barcelona benefits from VOC reductions (10 ppb of O 3 ) as well as the industrial zone of Alcover (20 ppb). The rest of the domain is practically insensitive to VOC reductions. Diverse photochemical species derived from the air quality model were used as indicators in order to establish the chemical sensitivity regime existing in the areas, analyzing whether O 3 values reacted consistently to similar changes in emissions. Results showed that NO y (total reactive nitrogen) and O 3 /NO y are the indicators involving a lower uncertainty when assessing sensitivity, according to the narrow transition regime between NO x ‐ and VOC‐sensitive chemistry and the low uncertainty observed. Indicators performed better in VOC‐sensitive than in NO x ‐sensitive domains. H 2 O 2 ‐ and HNO 3 ‐ derived indicators entailed higher uncertainties since transition regimes between NO x and VOC sensitivity covered a wide range. The extent of reaction also performed as a good indicator to separate NO x ‐ and VOC‐sensitive regimes. This sensitivity analysis provides a tool for establishing hypothetical control policies for O 3 precursor emissions through a comparison of simulated correlation between the species.