Ozone production during the field campaign RISFEX 2003 in the sea of Japan: analysis of sensitivity and behaviour based on an improved indicator
Abstract. The ratio Φ=kHC+OH[HC]/kNOx+OH[NOx] is used as an indicator for the sensitivity of ozone production (P(O3)) to HC and NOx in the field campaign RISFEX 2003 (RIShiri Fall EXperiment 2003) at Rishiri Island (45.07° N, 141.12° E, and 35 m a.s.l.) in the sea of Japan during September 2003. Four different sensitivity regimes are obtained based on the indicator. The sensitivity is found to show a distinctive pattern in each regime. In Regime I (Φ<1), P(O3) almost linearly increases with increasing HC and almost linearly decreases with increasing NOx. In Regime II (1<Φ<9 ± 5), there is a less-than-linear increase in P(O3) with HC and a less-than-linear decrease with NOx. P(O3) less-than-linearly increases with both HC and NOx in Regime III (9 ± 5<Φ<45 ± 7), and near linearly increases with NOx and is nearly constant with increasing HC in Regime IV (Φ>45 ± 7). During the campaign, 91 percent of P(O3) data appear in Regime III and IV, indicating that NOx is a limiting factor of ozone production. Hence, it may be an efficient strategy to control NOx emission for ozone abatement at the site.
Comparisons between the observed P(O3) and the ones modelled have represented general agreement. However, the model tends to underestimate P(O3) in Regime II, implying that an important source of peroxy radicals is possibly missed. In Regime IV, the modelled P(O3) is systematically larger than the measured one under a low j(O1D) condition, which may be caused by the over-estimated yields of peroxy radicals from the reactions of monoterpenes with ozone. A budget analysis indicates that sensitivity of P(O3) is declining with HC and enhancing with NO when the condition shifts from Regime II to Regime IV, which is also observed through the analysis of P(O3) sensitivity using Φ. Sensitivity studies for P(O3) are conducted to determine the effect of NOx and monoterpenes on ozone production and the conclusions are very consistent with those derived from the indicator. This study demonstrates that the ratio Φ could be a useful index to ascertain the sensitivity of P(O3) to HC and NOx in the clean marine boundary layer.
